Lighting device

Abstract

The invention relates to a lighting device. A lighting device and a method for calibrating and controlling individual LEDs in a lighting device to obtain a desired luminous flux and chromaticity of the device with variations in drive current, temperature, and with the time the LEDs age are provided. The lighting device may include a phosphor-converted LED configured to emit illumination to the lighting device, where a spectrum of illumination emitted from the phosphor-converted LED includes a first portion having a first peak emission wavelength and a second portion having a second peak emission wavelength different from the first peak emission wavelength. The method is used to calibrate and control each portion of the phosphor-converted LED spectrum as if the phosphor-converted LED is two separate LEDs. Also provided is a lighting device comprising one or more transmitter modules, the one or more transmitter modules having improved thermal and electrical characteristics.

Description

[0001] This divisional application is a divisional application based on the Chinese patent application with application number 202110903454.X, application date August 6, 2021, and invention name “Method for controlling a lighting device and a lighting device”, which is a divisional application based on the Chinese patent application with application number 201811213348.3, application date June 25, 2015, and invention name “LED lighting device and method for calibrating and controlling LED lighting device”, and the latter is a divisional application based on the Chinese patent application with application number 201580043185.7, application date June 25, 2015, and invention name “LED lighting device and method for calibrating and controlling LED lighting device with changes in temperature, driving current and time”. Technical Field

[0002] The present invention relates to lighting devices including a plurality of light emitting diodes (LEDs), and more particularly to lighting devices and methods for calibrating and controlling individual LEDs in a lighting device to obtain a desired luminous flux and chromaticity of the device over time as the drive current, temperature, and as the LEDs age. Also provided herein is a lighting device including one or more emitter modules having improved thermal and electrical characteristics. Background Art

[0003] The following description and examples are provided as background only and are intended to disclose information believed to be potentially relevant to the present invention. It is not necessarily intended or should be construed as an admission that any of the following information constitutes prior art that affects the patentable nature of the subject matter claimed herein.

[0004] Lamps and displays that use LEDs (light emitting diodes) for lighting are becoming increasingly popular in many different markets. Compared to traditional light sources such as incandescent or fluorescent bulbs, LEDs offer many advantages, including low power consumption, long life, no hazardous materials, and additional specific advantages for different applications. When used for general lighting, LEDs offer the opportunity to adjust the color (e.g., from white to blue, to green, etc.) or color temperature (e.g., from "warm white" to "cool white"), thereby producing different lighting effects.

[0005] Although LEDs have many advantages over conventional light sources, one disadvantage of LEDs is that their output characteristics (e.g., luminous flux and chromaticity) vary with driving current, temperature, and over time as the LED ages. These effects are particularly evident in multi-color LED lighting devices that combine many different color emitting LEDs into a single package.

[0006] An example of a multi-color LED lighting device is a multi-color LED lighting device in which two or more different colored LEDs are combined into the same package to produce white light or near-white light. There are many different types of white light lamps on the market, some of which combine red, green and blue (RGB) LEDs, red, green, blue and yellow (RGBY) LEDs, phosphor-converted white and red (WR) LEDs, RGBW LEDs, etc. By combining different colored LEDs into the same package and using different drive currents to drive the different colored LEDs, these lamps can be configured to generate a wide color gamut of color points or white light within a correlated color temperature (CCT) ranging from "warm white" (e.g., approximately 2600K-3700K) to "neutral white" (e.g., 3700K-5000K) to "cool white" (e.g., 5000K-8300K). Some multi-color LED lighting devices also enable the brightness and / or color of the lighting to be changed to a specific set point. These adjustable lighting devices should all produce the same color and color rendering index (CRI) when set to a specific dimming level and chromaticity setting (or color set point) on a standardized chromaticity diagram.

[0007] A chromaticity diagram plots the gamut of colors that the human eye can perceive in terms of chromaticity coordinates and spectral wavelengths. The spectral wavelengths of all saturated colors are distributed around the edge of the delineated space (called the "color gamut" of human vision), which includes all hues perceived by the human eye. The curved edge of the gamut is called the spectral locus and corresponds to monochromatic light, with each point representing a pure hue of a single wavelength. The straight edge on the lower part of the gamut is called the purple line. Although these colors are on the border of the gamut, they have no equivalent in monochromatic light. Undersaturated colors appear in the interior of the diagram, with white and near-white near the center.

[0008] In the 1931 CIE chromaticity diagram, colors in the color gamut of human vision are plotted according to chromaticity coordinates (x, y). For example, the chromaticity coordinates of a red (R) LED with a peak wavelength of 625 nm may be (0.69, 0.31), the chromaticity coordinates of a green (G) LED with a peak wavelength of 528 nm may be (0.18, 0.73), and the chromaticity coordinates of a blue (B) LED with a peak wavelength of 460 nm may be (0.14, 0.04). The chromaticity coordinates (i.e., color points) along the blackbody locus obey the Planck equation E(λ)=Aλ -5 / (e (B / T) -1). Color points on or near the blackbody locus provide a range of white or near-white light with a color temperature range between about 2500K and 10,000K. These color points are typically achieved by mixing light from two or more LEDs of different colors. For example, one can mix light from Figure 1The light emitted from the RGB LED shown in , thereby producing substantially white light with a color temperature ranging from about 2500K to about 5000K.

[0009] Although lighting devices are typically configured to produce a white or near-white temperature arranged along the black body curve (e.g., about 2500K to 5000K), some lighting devices can be configured to produce any color within the color gamut 18 (triangle) formed by individual LEDs (e.g., RGB). The chromaticity coordinates of the combined light (e.g., (0.437, 0.404) for 3000K white light) define the target chromaticity or color set point at which the device is intended to operate. In some devices, the target chromaticity or color set point can be changed by changing the ratio of the drive currents supplied to the individual LEDs.

[0010] Typically, the target chromaticity of a lighting device can be adjusted by adjusting the drive current level (in current dimming) or duty cycle (in PWM dimming) supplied to one or more of the emitting LEDs. For example, a lighting device including RGB LEDs can be configured to produce "warmer" white light by increasing the drive current supplied to the red LEDs and reducing the drive current supplied to the blue and / or green LEDs. Since adjusting the drive current also affects the lumen output and temperature of the lighting device, the target chromaticity must be carefully calibrated and controlled to ensure that the actual chromaticity is equal to the target value. Most prior art lighting devices fail to provide accurate calibration and compensation methods for controlling the color of the lighting device.

[0011] Some prior art lighting devices also provide dimming capabilities, that is, the ability to change the brightness or luminous flux output in the emitting LED in addition to (or instead of) color adjustment. In most cases, the dimming level is changed by adjusting the drive current level (in current dimming) or the duty cycle of the drive current supplied to all emitting LEDs (in PWM dimming) to supply a target dimming level. However, adjusting the supplied drive current changes the chromaticity of the lighting, and this chromaticity change varies for different LED devices and different dimming methods. For example, the chromaticity of an RGB LED lighting device may vary quite significantly with changes in the drive current level and duty cycle, while the chromaticity of a phosphor-converted white LED lighting device is more consistent. In order to maintain a consistent target chromaticity, a series of target chromaticity values ​​must be carefully calibrated through a series of target dimming levels.

[0012] In practice, the lumen output and chromaticity produced by prior art lighting devices often vary from the target dimming level and target chromaticity settings due to changes in temperature and over time as the LEDs age. Typically, changes in temperature affect the lumen output and chromaticity of all phosphor-converted LEDs and non-phosphor-converted LEDs. Although prior art devices can perform some level of temperature compensation, they are unable to provide accurate results because they fail to recognize that temperature affects the lumen output and chromaticity of different color LEDs to varying degrees. In addition, these prior art devices are unable to account for chromaticity shifts in the illumination produced by phosphor-converted LEDs, which are caused by phosphor aging. As a result, these prior art devices fail to maintain the desired luminous flux and desired chromaticity of the lighting device under operating conditions and over the life of the LED lighting device.

[0013] There remains a need for improved lighting devices and improved methods for calibrating and compensating individual LEDs within LED lighting devices to accurately maintain a desired luminous flux and a desired chromaticity of the lighting device over time as temperature changes, drive current changes, and as the LEDs age. This need is particularly warranted in multi-color LED lighting devices (because different color LEDs are affected by temperature and aging to different degrees) and in adjustable lighting devices that enable target dimming levels and / or target chromaticity settings to be changed by adjusting the drive current supplied to one or more of the LEDs (because changes in drive current inherently affect the lumen output, color, and temperature of the lighting device). Summary of the invention

[0014] The following description of various embodiments of a lighting device and a method for calibrating and controlling a lighting device should not be construed in any way as limiting the subject matter of the appended claims.

[0015] According to one embodiment, a method for calibrating individual LEDs in a light emitting diode (LED) lighting device is provided herein so that a desired luminous flux and a desired chromaticity of the device can be maintained over time with changes in drive current, temperature, and as the LED ages. Generally, the lighting device described herein may include multiple emitting LEDs or multiple emitting LED chains and at least one dedicated photodetector. For simplicity, the term "LED" will be used herein to refer to a single LED or a series-connected LED chain supplied with the same drive current. Although some of the methods described herein may only involve the first LED, the method may be performed for each emitting LED included in the lighting device.

[0016] According to one embodiment, a calibration method as provided herein may include subjecting a lighting device to a first ambient temperature and sequentially applying at least three different drive currents to a first LED of the lighting device, thereby producing illumination at three or more different brightness levels. At each of the at least three different drive currents, the calibration method may obtain a plurality of optical measurements from the illumination produced by the first LED and a plurality of electrical measurements from the at least one dedicated photodetector. In some embodiments, the plurality of optical measurements may include a plurality of luminous flux measurements and chromaticity measurements obtained from the illumination produced by the first LED at each of the at least three different drive currents.

[0017] In some embodiments, the plurality of electrical measurements may include a plurality of photocurrents induced on a photodetector by illumination generated by the first LED at each of the at least three different drive currents, and a plurality of forward voltages measured across the photodetector before, during, or after measuring each induced photocurrent. The forward voltage is typically measured across the photodetector by applying a non-operating drive current to the photodetector. Depending on the number of photodetectors included in the lighting device, the size of the photodetector(s), and how they are connected, the non-operating drive current applied to the photodetector for measuring the forward voltage may range between about 100 μA and about 1 mA.

[0018] In some embodiments, the calibration method can also measure the forward voltage generated across the anode and cathode of the first LED by applying a non-operating drive current to the first LED at a time before, during, or after measuring each induced photocurrent from the photodetector. Depending on the size of the first LED, the non-operating drive current applied to the first LED for measuring the forward voltage can range between about 1 mA and about 10 mA.

[0019] Typically, the drive current applied to the first LED for obtaining the luminous flux, chromaticity, and induced photocurrent measurements can be an operating drive current level (e.g., about 20 mA to about 500 mA), and thus can be substantially greater than the non-operating drive current supplied to the photodetector (e.g., about 0.1 mA to about 1 mA) and the non-operating drive current supplied to the first LED for measuring the forward voltage (e.g., about 0.1 mA to about 10 mA). In some cases, increasingly larger drive current levels can be applied to the first LED in succession to obtain the luminous flux, chromaticity, and induced photocurrent measurements. In other cases, the luminous flux, chromaticity, and induced photocurrent measurements can be obtained after successively applying gradually decreasing drive current levels to the first LED. Provided that the drive currents are different from one another, the order in which the drive currents are applied during the optical and electrical measurements is largely unimportant.

[0020] In one embodiment, after successively applying a first operating drive current, a second operating drive current substantially less than the first operating drive current, and a third operating drive current substantially less than the second operating drive current to the first LED, three luminous flux measurements, three x chromaticity measurements, three y chromaticity measurements, and three induced photocurrent measurements may be obtained from the first LED. In one example, the first operating drive current may be substantially equal to the maximum drive current associated with the first LED (e.g., approximately 500 mA, depending on the LED part number and manufacturer), the second operating drive current may be approximately 30% of the maximum drive current, and the third operating drive current may be approximately 10% of the maximum drive current. Although examples are provided herein, the calibration method is not limited to any particular value or any particular number of drive current levels, and substantially any value and / or any number of drive current levels within the operating current level range of the LED may be applied to the first LED. Furthermore, the calibration method is not limited to measuring chromaticity in only the CIE 1931 XYZ color space, and may additionally or alternatively measure chromaticity in any color space that may be used to describe the color gamut of an LED lighting device including a combination of emitting LEDs as described herein.

[0021] Sometime after obtaining the optical and electrical measurements at the first ambient temperature, the results of the obtaining step can be stored in the lighting device to calibrate the first LED at the first temperature. In one embodiment, the optical and electrical measurements obtained at the first ambient temperature can be stored in a calibration value table.

[0022] In some cases, the calibration method can continue by subjecting the lighting device to a second ambient temperature different from the first ambient temperature, and repeating the steps of: successively applying the at least three different drive currents to the first LED; obtaining a plurality of optical measurements from the illumination produced by the first LED at each of the at least three different drive currents; obtaining a plurality of electrical measurements from the photodetector; and storing the results of the obtaining steps in the lighting device to calibrate the first LED at the second ambient temperature. In one embodiment, the optical and electrical measurements obtained at the second ambient temperature can be stored in a calibration value table.

[0023] In one embodiment, the second ambient temperature may be substantially less than the first ambient temperature. For example, the second ambient temperature may be approximately equal to room temperature (e.g., approximately 25° C.), and the first ambient temperature may be substantially greater than room temperature. In one example, the first ambient temperature may be closer to an elevated temperature (e.g., approximately 70° C.) or a maximum temperature (e.g., approximately 80° C.) at which the device is expected to operate. In an alternative embodiment, the second ambient temperature may be substantially greater than the first ambient temperature.

[0024] It is worth noting that the exact values, number, and order of temperatures applied to calibrate the first LED are somewhat unimportant. However, it is generally desirable to obtain luminous flux and chromaticity measurements from the first LED and photocurrent measurements from the photodetector(s) at a sufficient number of different drive current levels such that the nonlinear relationship between these measurements and the drive current can be accurately characterized across the range of operating current levels of the first LED. In an exemplary embodiment, the lighting device can be subjected to two (or more) substantially different ambient temperatures selected from within the operating temperature range of the lighting device.

[0025] According to another embodiment, a lighting device having a plurality of light emitting diode (LED) chains configured to generate illumination for the lighting device is provided herein, and a photodetector configured to detect the illumination generated by each of the plurality of LED chains. Typically, each LED chain may include one or more LEDs of the same color. In some embodiments, each LED chain may be configured to generate illumination having a different peak emission wavelength. In other embodiments, two or more LED chains may be configured to generate illumination having the same peak emission wavelength.

[0026] The lighting device may further include an LED driver and receiver circuit, the LED driver and receiver circuit being configured to: continuously apply the at least three different drive currents to each LED chain in the LED chain one LED chain at a time when the LED chain is subjected to a first ambient temperature so as to produce illumination at different brightness levels; measure the photocurrent induced on the photodetector by the illumination produced by each LED chain in the LED chain under each of the at least three different drive currents; and measure the forward voltage generated across the photodetector before, during or after measuring each induced photocurrent. In addition, the LED driver and receiver circuit is further configured to repeat the following steps: continuously apply at least three different drive currents to each LED chain in the LED chain; measure the photocurrent induced on the photodetector; and measure the forward voltage generated across the photodetector when the LED chain is subjected to a second ambient temperature different from the first ambient temperature.

[0027] The lighting device may further include an interface configured to receive luminous flux measurements and chromaticity measurements, the luminous flux measurements and chromaticity measurements being measured by an external calibration tool after receiving illumination produced by each of the LED chains at each of the at least three different drive currents when the LED chains are subjected to the first and second ambient temperatures. In one embodiment, the interface may be a wireless interface configured to communicate using radio frequency (RF), infrared (IR) light, or visible light. For example, the wireless interface may be configured to operate according to at least one of a ZigBee, WiFi, or Bluetooth communication protocol. In another embodiment, the interface may be a wired interface configured to communicate over an AC power source, a dedicated conductor, or a set of conductors.

[0028] The lighting device may further include a storage medium configured to store the photocurrent, forward voltage, luminous flux, and chromaticity measurements obtained for each of the LED chains in a calibration value table. In some embodiments, the photocurrent, forward voltage, luminous flux, and chromaticity measurements stored in the storage medium may include measurements obtained from the LED driver and receiver circuits and an external calibration tool. In other embodiments, the measurements may be used to calculate calibration coefficients in addition to or in lieu of the received calibration values, which are stored in the storage medium.

[0029] According to one embodiment, for each LED chain, the calibration value table may include: a first plurality of photocurrent values, the first plurality of photocurrent values ​​being obtained from the photodetector after receiving illumination from the LED chain when the LED chain is subjected to a first ambient temperature and the at least three different drive currents are continuously applied to the LED chain; a second plurality of photocurrent values, the second plurality of photocurrent values ​​being obtained from the photodetector after receiving illumination from the LED chain when the LED chain is subjected to a second ambient temperature and the at least three different drive currents are continuously applied to the LED chain; and a plurality of forward voltage values, the plurality of forward voltage values ​​being measured across the photodetector before, during or after measuring each photocurrent value.

[0030] In some embodiments, the LED driver and receiver circuits may be further configured to apply a non-operating drive current to each LED chain, and to measure a forward voltage generated across each LED chain before, during, or after measuring each induced photocurrent. In such embodiments, for each LED chain, the calibration value table may include: a first plurality of forward voltage values ​​measured across the LED chain after the non-operating drive current is applied to the LED chain when the LED chain is subjected to a first ambient temperature; and a second plurality of forward voltage values ​​measured across the LED chain after the non-operating drive current is applied to the LED chain when the LED chain is subjected to a second ambient temperature.

[0031] In some embodiments, for each LED chain, the calibration value table may further include: a first plurality of luminous flux values, wherein the first plurality of luminous flux values ​​are detected from the LED chain after applying the at least three different driving currents to the LED chain when the LED chain is subjected to a first ambient temperature; and a second plurality of luminous flux values, wherein the second plurality of luminous flux values ​​are detected from the LED chain after applying the at least three different driving currents to the LED chain when the LED chain is subjected to a second ambient temperature.

[0032] In some embodiments, for each LED chain, the calibration value table may further include: a first plurality of x chromaticity values ​​and a first plurality of y chromaticity values, the first plurality of x chromaticity values ​​and the first plurality of y chromaticity values ​​being detected from the LED chain after applying the at least three different drive currents to the LED chain when the LED chain is subjected to a first ambient temperature; and a second plurality of x chromaticity values ​​and a second plurality of y chromaticity values ​​being detected from the LED chain after applying the at least three different drive currents to the LED chain when the LED chain is subjected to a second ambient temperature. However, the calibration value table is not limited to storing only chromaticity values ​​from the CIE 1931 XYZ color space, and may additionally or alternatively store chromaticity values ​​from any color space of the color gamut of an LED lighting device including a combination of emitting LEDs as described herein.

[0033] In some embodiments, the lighting device may further include an additional photodetector configured to detect illumination generated by a subset of the plurality of LED chains. In one example, the subset of LED chains may include a phosphor-converted LED chain (e.g., a phosphor-converted white LED chain) and a reference LED chain (e.g., a blue LED chain).

[0034] In this embodiment, the LED driver and receiver circuit can be further configured to: measure the photocurrent induced on the additional photodetector by the phosphor-converted LED chain and the reference LED chain individually at each of the at least three different drive currents when the LED chain is subjected to the first and second ambient temperatures; and measure the forward voltage generated across the additional photodetector before, during or after measuring each induced photocurrent.

[0035] In such an embodiment, for each LED chain in the subset, the calibration value table may further include: a first plurality of photocurrent values ​​obtained from the additional photodetector after receiving illumination from the LED chain when the LED chain is subjected to a first ambient temperature and the at least three different drive currents are continuously applied to the LED chain; a second plurality of photocurrent values ​​obtained from the additional photodetector after receiving illumination from the LED chain when the LED chain is subjected to a second ambient temperature and the at least three different drive currents are continuously applied to the LED chain; and a plurality of forward voltage values ​​measured across the additional photodetector before, during, or after measuring each photocurrent value. The induced photocurrent and the forward voltage measured across the additional photodetector may be stored in the storage medium as measured values ​​or calculated coefficients.

[0036] According to another embodiment, a first compensation method for controlling an LED lighting device so that a desired luminous flux and a desired chromaticity of the device can be maintained as temperature and drive current change, is provided herein. Generally, the first compensation method can be initiated by applying a corresponding drive current to the plurality of emitting LEDs so as to substantially continuously drive the plurality of emitting LEDs to produce illumination; periodically turning off the plurality of emitting LEDs for a short duration; and during the short duration of periodically turning off the plurality of emitting LEDs, by applying a non-operating drive current to each emitting LED one LED at a time, measuring the forward voltage currently generated across each emitting LED. As used herein, the non-operating drive current can be described as a drive current level that is insufficient to produce significant illumination from the LED and can range between about 0.1 mA and about 10 mA.

[0037] The first compensation method described herein may further include: using the forward voltage measured across each emitting LED, the corresponding drive current supplied to each emitting LED, a stored calibration value table relating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques to determine the expected chromaticity value for each emitting LED. In some embodiments, the method may further include: monitoring a target brightness setting and a target chromaticity setting of the lighting device; and performing the measuring and determining steps only when a change in at least one of the target brightness setting and the target chromaticity setting is detected.

[0038] Typically, the stored calibration value table may include chromaticity calibration values ​​corresponding to the CIE 1931 XYZ color space, the CIE 1931 RGB color space, the CIE 1976 LUV color space, or various other RGB color spaces (e.g., sRGB, Adobe RGB, etc.). Although the first compensation method described herein may utilize only x and y chromaticity calibration values, those skilled in the art will understand how to alternatively obtain chromaticity values ​​from other color spaces and how to use them in the methods described herein. As such, the first compensation method is considered to include chromaticity calibration values ​​from any color space that can be used to describe the color gamut of an LED lighting device that substantially includes any combination of emitting LEDs as described herein.

[0039] According to one embodiment, for each emitting LED, the stored calibration value table may include: a first plurality of x chromaticity values ​​and a first plurality of y chromaticity values, wherein the first plurality of x chromaticity values ​​and the first plurality of y chromaticity values ​​were previously detected from the emitting LED after applying a plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED was subjected to a first temperature; and a second plurality of x chromaticity values ​​and a second plurality of y chromaticity values, wherein the second plurality of x chromaticity values ​​and the second plurality of y chromaticity values ​​were previously detected from the emitting LED after applying the plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED was subjected to a second temperature.

[0040] In addition, the calibration value table may include a first plurality of forward voltage values ​​and a second plurality of forward voltage values ​​for each emitting LED. The first plurality of forward voltage values ​​may be forward voltage values ​​measured across the emitting LED before, during, or after each of the different drive currents is applied to the emitting LED, and after a non-operating drive current is applied to the emitting LED when the emitting LED is subjected to a first temperature. The second plurality of forward voltage values ​​may be forward voltage values ​​measured across the emitting LED before, during, or after each of the different drive currents is applied to the emitting LED, and after a non-operating drive current is applied to the emitting LED, when the emitting LED is subjected to a second temperature.

[0041] In one embodiment, the expected x chromaticity value of each emitting LED may be determined by calculating a third plurality of x chromaticity values ​​corresponding to a forward operating voltage measured across the emitting LED by interpolating between the first plurality of x chromaticity values ​​and the second plurality of x chromaticity values; generating a relationship between the third plurality of x chromaticity values ​​if the corresponding drive current supplied to the emitting LED is different from one of a plurality of different drive currents applied to the emitting LED during a calibration phase; and determining the expected x chromaticity value of the emitting LED corresponding to the corresponding drive current applied to the emitting LED based on the generated relationship.

[0042] In one embodiment, the expected y chromaticity value of each emitting LED can be determined by: calculating a third plurality of y chromaticity values ​​corresponding to the forward operating voltage measured across the emitting LED by interpolating between the first plurality of y chromaticity values ​​and the second plurality of y chromaticity values; generating a relationship between the third plurality of y chromaticity values ​​if the corresponding drive current supplied to the LED is different from one of the plurality of different drive currents applied to the emitting LED during the calibration phase; and determining the expected y chromaticity value of the emitting LED corresponding to the corresponding drive current applied to the emitting LED based on the generated relationship.

[0043] In some cases, the steps of calculating the third plurality of x-chromaticity values ​​and the third plurality of y-chromaticity values ​​may each include interpolating between the first and second plurality of x- and y-chromaticity values ​​using a linear interpolation technique. In some cases, the step of generating a relationship may include applying a higher order interpolation to the third plurality of x- and y-chromaticity values ​​to generate a nonlinear relationship between the x- and y-chromaticity and the drive current at the forward voltage measured across the emitting LED. In other cases, the step of generating a relationship may include applying a piecewise linear interpolation to the third plurality of x- and y-chromaticity values ​​to approximate the nonlinear relationship between the x- and y-chromaticity and the drive current at the forward voltage measured across the emitting LED. In still other cases, the step of generating a relationship may include assuming a typical curvature from a data sheet provided by an LED manufacturer.

[0044] In some embodiments, the first compensation method may further include a relative luminous flux required from each emitting LED to achieve a target brightness setting and a target chromaticity setting of the lighting device. Typically, the relative luminous flux of each emitting LED is calculated using the target brightness setting, the target chromaticity setting, the expected x chromaticity value and the expected y chromaticity value determined according to the generated relationship.

[0045] In some embodiments, the first compensation method may further include: determining the drive current required to achieve the relative luminous flux calculated for the emitting LED using: a forward voltage measured across each emitting LED, a stored calibration value table, and one or more interpolation techniques; and driving each emitting LED using the determined drive current to produce illumination having the calculated relative luminous flux.

[0046] In addition to correlating the forward voltage to the drive current at a plurality of different temperatures, the stored calibration value table may further correlate the forward voltage and the drive current to the luminous flux at a plurality of different temperatures. For example, for each emitting LED, the stored calibration value table may include: a first plurality of luminous flux values, the first plurality of luminous flux values ​​being previously detected from the emitting LED during a calibration phase when the emitting LED was subjected to a first temperature after applying a plurality of different drive currents to the emitting LED; and a second plurality of luminous flux values, the second plurality of luminous flux values ​​being previously detected from the emitting LED during a calibration phase when the emitting LED was subjected to a second temperature after applying a plurality of different drive currents to the emitting LED.

[0047] For each emitting LED, the step of determining the driving current may include: calculating a third plurality of luminous flux values ​​corresponding to the forward voltage measured across the emitting LED by interpolating between the first plurality of luminous flux values ​​and the second plurality of luminous flux values; generating a relationship between the third plurality of luminous flux values ​​if the relative luminous flux calculated for the emitting LED is different from one of the third plurality of luminous flux values; and determining the driving current required to achieve the calculated relative luminous flux by selecting a driving current corresponding to the calculated relative luminous flux from the generated relationship.

[0048] In some cases, the third plurality of luminous flux values ​​may be calculated by interpolating between the first and second plurality of luminous flux values ​​using a linear interpolation technique or a nonlinear interpolation technique. Typically, the selection between the linear interpolation technique and the nonlinear interpolation technique is made independently for each emitting LED based on the color of the emitting LED.

[0049] In some cases, the relationship may be generated by applying a higher order interpolation to the third plurality of luminous flux values ​​to generate a nonlinear relationship between luminous flux and drive current. In other cases, the relationship may be generated by applying a piecewise linear interpolation to the third plurality of luminous flux values ​​to approximate the nonlinear relationship between luminous flux and drive current. In still other cases, the relationship may be generated by assuming a typical curvature from a data sheet provided by an LED manufacturer.

[0050] According to another embodiment, a lighting device is provided herein, the lighting device having a plurality of emitting light emitting diodes (LEDs), a storage medium, an LED driver and a receiver circuit and a control circuit. A plurality of light emitting diode (LED) chains can generally be configured to generate illumination for the lighting device. In some embodiments, each emitting LED can be configured to generate illumination of a different peak wavelength. However, in other embodiments, one or more of the emitting LEDs can be configured to generate illumination of the same peak emission wavelength.

[0051] The storage medium may be generally configured to store a calibration value table that relates forward voltage and drive current to chromaticity and luminous flux at multiple temperatures for each of the plurality of emitting LEDs. Typically, the calibration value table stored in the storage medium may include chromaticity calibration values ​​corresponding to the CIE 1931 XYZ color space, the CIE 1931 RGB color space, the CIE 1976 LUV color space, or various other RGB color spaces (e.g., sRGB, Adobe RGB, etc.).

[0052] According to one embodiment, for each emitting LED, the calibration value table may include: a first plurality of x chromaticity values ​​and a first plurality of y chromaticity values, the first plurality of x chromaticity values ​​and the first plurality of y chromaticity values ​​being previously detected from the emitting LED after applying a plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED is subjected to a first temperature. The calibration value table may also include, for each emitting LED: a second plurality of x chromaticity values ​​and a second plurality of y chromaticity values, the second plurality of x chromaticity values ​​and the second plurality of y chromaticity values ​​being previously detected from the emitting LED after applying a plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED is subjected to a second temperature.

[0053] In addition, the calibration value table may include a first plurality of forward voltage values ​​and a second plurality of forward voltage values ​​for each emitting LED. The first plurality of forward voltage values ​​may be forward voltage values ​​measured across the emitting LED before, during, or after each of the different drive currents is applied to the emitting LED, and after a non-operating drive current is applied to the emitting LED when the emitting LED is subjected to a first temperature. The second plurality of forward voltage values ​​may be forward voltage values ​​measured across the emitting LED before, during, or after each of the different drive currents is applied to the emitting LED, and after a non-operating drive current is applied to the emitting LED, when the emitting LED is subjected to a second temperature.

[0054] In addition, the calibration value table may further include a first plurality of luminous flux values ​​and a second plurality of luminous flux values ​​for each emitting LED. The first plurality of luminous flux values ​​may be luminous flux values ​​previously detected from the emitting LED after applying a plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED was subjected to a first temperature. The second plurality of luminous flux values ​​may be luminous flux values ​​previously detected from the emitting LED after applying a plurality of different drive currents to the emitting LED during a calibration phase when the emitting LED was subjected to a second temperature.

[0055] The LED driver and receiver circuits may generally be configured to: apply corresponding drive currents to a plurality of transmit LEDs so as to substantially continuously drive the plurality of transmit LEDs to produce illumination; periodically turn off the plurality of transmit LEDs for a short duration; and apply a non-operating drive current to each transmit LED one LED at a time during the short duration so as to measure an operating forward voltage generated across each transmit LED. As used herein, a non-operating drive current may be described as a drive current level that is insufficient to produce significant illumination from an LED and may range between about 0.1 mA and about 10 mA.

[0056] In some embodiments, the lighting device may further include a phase locked loop (PLL) coupled to the AC power source and configured to generate a timing signal in synchronization with the frequency of the AC power source. In such embodiments, the timing signal may be supplied to the LED driver and receiver circuits to periodically turn off the plurality of transmitting LEDs for a short duration.

[0057] The control circuitry may be coupled to the LED driver and receiver circuitry and the storage medium. In some embodiments, the control circuitry may be configured to determine whether a target brightness setting or a target chromaticity setting of the lighting device has changed, and if so, to determine a new corresponding drive current required to achieve the target brightness setting and the target chromaticity setting using: an operating forward voltage measured across each emitting LED, a table of calibration values, and one or more interpolation techniques.

[0058] In some embodiments, the lighting device may further include a temperature sensor configured to detect an ambient temperature around the plurality of emitting LEDs. If the target brightness setting and the target chromaticity setting of the lighting device have not changed, the control circuit may be further configured to determine the corresponding drive current required to achieve the target brightness setting and the target chromaticity setting only when the ambient temperature changes by a specified amount.

[0059] For each LED chain, the control circuit may be configured to: calculate a third plurality of x chromaticity values ​​corresponding to an operating forward voltage measured across the emitting LED by interpolating between the first plurality of x chromaticity values ​​and the second plurality of x chromaticity values; generate a relationship between the third plurality of x chromaticity values ​​if the corresponding drive current applied to the emitting LED is different from one of the plurality of different drive currents applied to the emitting LED during the calibration phase; and determine an expected x chromaticity value of the emitting LED corresponding to the corresponding drive current applied to the emitting LED based on the generated relationship. For each emitting LED, the control circuit may be further configured to: calculate a third plurality of y chromaticity values ​​corresponding to an operating forward voltage measured across the emitting LED by interpolating between the first plurality of y chromaticity values ​​and the second plurality of y chromaticity values; generate a relationship between the third plurality of y chromaticity values ​​if the corresponding drive current applied to the emitting LED is different from one of the plurality of different drive currents applied to the emitting LED during the calibration phase; and determine an expected y chromaticity value of the emitting LED corresponding to the corresponding drive current applied to the emitting LED based on the generated relationship.

[0060] In some cases, the control circuit can be configured to calculate a third plurality of x and y chromaticity values ​​for each emitting LED by interpolating between the first and second plurality of x and y chromaticity values ​​corresponding to each emitting LED using a linear interpolation technique. In some cases, the control circuit can be configured to apply a higher order interpolation to the third plurality of x and y chromaticity values ​​to generate a nonlinear relationship between the x and y chromaticity and the drive current for each emitting LED. In other cases, the control circuit can be configured to apply a piecewise linear interpolation to the third plurality of x and y chromaticity values ​​to approximate the nonlinear relationship between the x and y chromaticity and the drive current for each emitting LED.

[0061] In some embodiments, the control circuit can be further configured to calculate the relative luminous flux required from each emitting LED to achieve the target brightness setting and the target chromaticity setting. In general, the control circuit can calculate the relative luminous flux of each emitting LED using the target brightness setting and the target chromaticity setting, and the expected x and y chromaticity values ​​determined based on the generated relationship.

[0062] In some embodiments, the control circuit can be further configured to determine the drive current required to achieve the calculated relative luminous flux for each emitting LED using: an operating forward voltage measured across the emitting LED, a stored calibration value table, and one or more interpolation techniques. In such embodiments, the LED driver and receiver circuit can be further configured to drive each emitting LED using the determined drive current to produce illumination having the calculated relative luminous flux.

[0063] In some embodiments, the control circuit can be configured to: calculate a third plurality of luminous flux values ​​corresponding to an operating forward voltage measured across the emitting LED by interpolating between the first plurality of luminous flux values ​​and the second plurality of luminous flux values ​​to thereby determine the driving current required to achieve the relative luminous flux calculated for each emitting LED; generate a relationship between the third plurality of luminous flux values ​​if the relative luminous flux calculated for the emitting LED is different from one of the third plurality of luminous flux values; and determine the driving current required to achieve the calculated relative luminous flux by selecting a driving current corresponding to the calculated relative luminous flux from the generated relationship.

[0064] In some cases, the control circuit is configured to calculate a third plurality of luminous flux values ​​for each emitting LED by interpolating between the first and second plurality of luminous flux values ​​corresponding to each emitting LED using a linear interpolation technique or a nonlinear interpolation technique. Typically, the selection between the linear interpolation technique and the nonlinear interpolation technique is made independently for each emitting LED based on the color of the emitting LED.

[0065] In some cases, the control circuit can be configured to generate the relationship by applying a higher order interpolation to the third plurality of luminous flux values ​​to generate a nonlinear relationship between the luminous flux of each emitting LED and the drive current. In other cases, the control circuit can be configured to generate the relationship by applying a piecewise linear interpolation to the third plurality of luminous flux values ​​to approximate the nonlinear relationship between the luminous flux of each emitting LED and the drive current. In still other cases, the control circuit can be configured to generate the relationship by assuming a typical curvature from a data sheet provided by a manufacturer of the emitting LED.

[0066] According to yet another embodiment, a second compensation method for controlling an LED lighting device so that a desired luminous flux and a desired chromaticity of the device can be maintained over time as the LEDs age is provided herein. In general, the second compensation method can be initiated by applying a drive current to a plurality of LED chains substantially continuously to generate illumination; measuring a photocurrent induced on the photodetector in response to illumination generated by each LED chain one LED chain at a time and received by the photodetector; and measuring a forward voltage generated across the photodetector by applying a non-operating drive current to the photodetector. In some embodiments, the second compensation method can further include periodically turning off the plurality of LED chains for a short duration, and measuring the photocurrent induced on the photodetector and the forward voltage generated across the photodetector one at a time during the short duration.

[0067] The second compensation method may further include determining, for each LED chain, an expected photocurrent value corresponding to the forward voltage measured across the photodetector and the drive current currently applied to the LED chain by applying one or more interpolation techniques to a stored calibration value table that relates the forward voltage and photocurrent to the drive current at multiple different temperatures.

[0068] In one embodiment, for each LED chain, the stored calibration value table may include: a first plurality of stored photocurrent values, a second plurality of stored photocurrent values, and a plurality of stored forward voltage values. The first plurality of stored photocurrent values ​​may be photocurrent values ​​previously obtained from a photodetector after receiving illumination from the LED chain when the LED chain was subjected to a first temperature and a plurality of drive currents were continuously applied to the LED chain. The second plurality of stored photocurrent values ​​may be photocurrent values ​​previously obtained from a photodetector after receiving illumination from the LED chain when the LED chain was subjected to a second temperature and the plurality of drive currents were continuously applied to the LED chain. The plurality of stored forward voltage values ​​may be forward voltage values ​​previously obtained across the photodetector after obtaining each of the first and second plurality of photocurrent values. In some embodiments, the first plurality of stored photocurrent values, the second plurality of stored photocurrent values, and the plurality of stored forward voltage values ​​may include measured values. In other embodiments, the measured values ​​may be used to calculate calibration coefficients, which are stored in the stored calibration value table in addition to or in lieu of the measured values.

[0069] In one embodiment, the expected photocurrent value for each LED may be determined by calculating a third plurality of photocurrent values ​​corresponding to the measured forward voltage by interpolating between a first plurality of stored photocurrent values ​​and a second plurality of stored photocurrent values ​​corresponding to the LED chain; generating a relationship between the third plurality of photocurrent values; and selecting an expected photocurrent value corresponding to the drive current currently applied to the LED chain from the generated relationship. In some cases, the third plurality of photocurrent values ​​may be calculated by interpolating between the first and second plurality of stored photocurrent values ​​corresponding to the LED chain using a nonlinear interpolation technique. In some cases, the relationship may be generated by applying a higher order interpolation to the third plurality of photocurrent values ​​so as to generate a nonlinear relationship between the photocurrent and the drive current of the LED chain. However, in other cases, the relationship may be generated by applying a piecewise linear interpolation to the third plurality of photocurrent values ​​so as to approximate the nonlinear relationship between the photocurrent and the drive current of the LED chain.

[0070] The second compensation method may further include: for each LED chain, if there is a difference between the expected photocurrent value and the measured photocurrent, adjusting the driving current currently applied to the LED chain. In some embodiments, the driving current may be adjusted by: calculating a proportionality factor of the LED chain by dividing the expected photocurrent value by the measured photocurrent; applying the proportionality factor to the desired luminous flux value of the LED chain to obtain an adjusted luminous flux value; and adjusting the driving current currently applied to the LED chain to achieve the adjusted luminous flux value.

[0071] According to another embodiment, a lighting device is provided herein, the lighting device having a plurality of light emitting diode (LED) chains, an LED driver and receiver circuit, a photodetector, a storage medium, and a control circuit. The plurality of light emitting diode (LED) chains may generally be configured to generate illumination for the lighting device. The photodetector may generally be configured to detect the illumination generated by the plurality of LED chains. The storage medium may generally be configured to store a calibration value table that relates a forward voltage and a photocurrent previously measured from the photodetector to a drive current previously applied to each of the LED chains at a plurality of different temperatures during calibration of the lighting device.

[0072] The LED driver and receiver circuitry may generally be configured to apply a drive current to the plurality of LED chains substantially continuously to produce illumination. In addition, the LED driver and receiver circuitry may be further configured to: measure a photocurrent induced on a photodetector in response to illumination produced by each LED chain one LED chain at a time and received by the photodetector; measure a forward voltage produced across the photodetector to provide a current temperature measurement; and supply the measured photocurrent and the measured forward voltage to the control circuitry.

[0073] The control circuit may be coupled to the LED driver and receiver circuit, the photodetector, and the storage medium, and may generally be configured to determine an expected photocurrent value for each LED chain from a stored table of calibration values ​​using a current temperature measurement and a drive current currently applied to each LED chain. In addition, the control circuit may be further configured to adjust the drive current currently applied by the LED driver and receiver circuit to each LED chain to produce illumination if the expected photocurrent value determined by the control circuit for the LED chain is different from the photocurrent measured by the LED driver and receiver circuit for the LED chain. For example, for each LED chain, the control circuit is further configured to: calculate a scaling factor by dividing the expected photocurrent value by the photocurrent measured by the LED driver and receiver circuit; apply the scaling factor to the desired luminous flux value to obtain an adjusted luminous flux value; and adjust the drive current currently applied to the LED chain to achieve the adjusted luminous flux value.

[0074] In some embodiments, the control circuit can be configured to determine the expected photocurrent value for each LED chain by using: the forward voltage measured by the LED driver and receiver circuit, the drive current currently applied to the LED chain by the LED driver and receiver circuit to produce lighting, a calibration value table, and one or more interpolation techniques.

[0075] For example, for each LED chain, the calibration value table may include: a first plurality of stored photocurrent values, a second plurality of stored photocurrent values, and a plurality of stored forward voltage values. The first plurality of stored photocurrent values ​​may be photocurrent values ​​previously obtained from a photodetector after receiving illumination from the LED chain when the LED chain was subjected to a first temperature and a plurality of drive currents were continuously applied to the LED chain. The second plurality of stored photocurrent values ​​may be photocurrent values ​​previously obtained from a photodetector after receiving illumination from the LED chain when the LED chain was subjected to a second temperature and the plurality of drive currents were continuously applied to the LED chain. The plurality of stored forward voltage values ​​may be forward voltage values ​​previously measured across the photodetector before, during, or after obtaining each of the first and second plurality of photocurrents. In some embodiments, the first plurality of stored photocurrent values, the second plurality of stored photocurrent values, and the plurality of stored forward voltage values ​​may include measured values. In other embodiments, the measured values ​​may be used to calculate calibration coefficients, which are stored in the calibration value table in addition to or in lieu of the measured values.

[0076] In some embodiments, the control circuit can be configured to determine the expected photocurrent value for each LED chain by calculating a third plurality of photocurrent values ​​corresponding to the forward voltage measured by the LED driver and receiver circuit by interpolating between the first plurality of stored photocurrent values ​​and the second plurality of stored photocurrent values ​​corresponding to the LED chain; generating a relationship between the third plurality of photocurrent values; and selecting the expected photocurrent value corresponding to the drive current currently applied to the LED chain by the LED driver and receiver circuit from the generated relationship. In some cases, the control circuit can be configured to calculate the third plurality of photocurrent values ​​by interpolating between the first and second plurality of stored photocurrent values ​​using a nonlinear interpolation technique. In some cases, the control circuit can be configured to generate the relationship by applying a higher order interpolation to the third plurality of photocurrent values ​​to generate a nonlinear relationship between the photocurrent and the drive current of the LED chain. In other cases, the control circuit can be configured to generate the relationship by applying a piecewise linear interpolation to the third plurality of photocurrent values ​​to approximate the nonlinear relationship between the photocurrent and the drive current of the LED chain.

[0077] The lighting devices and methods described above are generally suitable for calibrating and controlling LED lighting devices that include non-phosphor converted LEDs. In addition to the lighting devices and methods described above, a method for calibrating and controlling an LED lighting device that includes at least one phosphor converted LED is also provided herein. An example of a phosphor converted LED is a phosphor converted white LED formed by coating or covering, for example, a blue LED having a peak emission wavelength of about 400 to 500 with a phosphor material (e.g., YAG) for producing substantially white light having a correlated color temperature (CCT) of about 3000K. Other combinations of LEDs and phosphors can be used to form phosphor converted white LEDs that can produce white light or near white light with a CCT in the range of about 2700K to 10,000K.

[0078] In a phosphor-converted white LED, the spectral content of the LED is combined with the spectral content of the phosphor to produce white light or near-white light. The combined spectrum can include a first portion having a first peak emission wavelength (e.g., about 400 to 500) and a second portion having a second peak emission wavelength substantially different from the first peak emission wavelength (e.g., about 500 to 650). In this example, the first portion of the spectrum is generated by light emitted by a blue LED, and the second portion is generated by light passing through a phosphor (e.g., YAG).

[0079] As a phosphor-converted white LED ages, the efficiency of the phosphor decreases, which causes the chromaticity of the phosphor-converted white LED to appear "colder" over time. In order to account for aging-related chromaticity shifts in phosphor-converted LEDs, the lighting device described herein may include two different photodetectors for respectively measuring a photocurrent induced in an LED portion and a photocurrent induced in a phosphor portion of the phosphor-converted LED. In an exemplary embodiment, the lighting device may include a first photodetector having a detection range configured to detect only the first portion of the spectrum emitted by the phosphor-converted LED; and a second photodetector having a detection range configured to detect only the second portion of the spectrum emitted by the phosphor-converted LED.

[0080] Typically, the detection ranges of the first and second photodetectors can be selected based on the spectrum of the phosphor-converted LED being measured. In an exemplary embodiment in which the phosphor-converted white LED described above is included in the lighting device and implemented in the manner described above, the detection range of the first photodetector can be between about 400nm and about 500nm to measure the photocurrent induced by light emitted by the blue LED portion, and the detection range of the second photodetector can be between about 500nm and about 650nm to measure the photocurrent induced by light passing through the phosphor portion of the phosphor-converted white LED. The first and second photodetectors can include dedicated photodetectors and / or emitting LEDs that are sometimes configured to detect incident light.

[0081] In some embodiments, the lighting device may further include a reference LED (e.g., a blue emitting LED) having a peak emission wavelength that falls within the first portion of the spectrum emitted by the phosphor-converted LED. In some embodiments, if such a reference LED is included, the photocurrent induced on the first and second photodetectors by the illumination produced by the reference LED may be used to account for detector aging when adjusting the chromaticity of the phosphor-converted white LED.

[0082] In some embodiments, the lighting device may include other emitting LEDs in addition to the phosphor-converted LEDs and the optional reference LED (which may also be an emitting LED). In addition to the emitting LEDs and the photodetector, the lighting devices described herein may also generally include LED driver and receiver circuits, storage media, and control circuits. Other components not specifically mentioned herein may also be included.

[0083] During the calibration phase, while the lighting device is subjected to a first ambient temperature, the LED driver and receiver circuit may apply a plurality of different drive currents to the phosphor-converted LED and the reference LED in succession, producing illumination at different brightness levels, one LED at a time. At each of the different drive currents, the LED driver and receiver circuit measures the photocurrent induced on the first and second photodetectors by the illumination produced by the phosphor-converted LED, and measures the forward voltage produced across the first and second photodetectors before, during, or after measuring each induced photocurrent. Once the induced current and forward voltage measurements are obtained, the LED driver and receiver circuit repeats the steps of: applying a plurality of different drive currents to the phosphor-converted LED in succession; measuring the photocurrent induced on the first and second photodetectors; and measuring the forward voltage produced across the first and second photodetectors when the lighting device is subjected to a second ambient temperature different from the first ambient temperature. In some embodiments, the LED driver and receiver circuit may also measure the photocurrent induced on the first and second photodetectors by the illumination produced by the reference LED at each of the different drive currents and at each of the first and second ambient temperatures. The photocurrent and forward voltage measurements obtained by the LED driver and receiver circuit during the calibration phase may be stored in a table of calibration values ​​within a storage medium of the lighting device.

[0084] During operation of the lighting device, the LED driver and receiver circuit can be configured to apply a drive current to the phosphor-converted LED substantially continuously to generate illumination; and to measure photocurrents induced on the first and second photodetectors in response to the illumination generated by the phosphor-converted LED and received by the first and second photodetectors. Specifically, the LED driver and receiver circuit can measure a first photocurrent induced on the first photodetector and a second photocurrent induced on the second photodetector in response to the illumination generated by the phosphor-converted LED. The first photocurrent can correspond to the first portion of the spectrum of the phosphor-converted LED, and the second photocurrent can correspond to the second portion of the spectrum of the phosphor-converted LED. In some embodiments, the LED driver and receiver circuit can also measure a third photocurrent induced on the first photodetector and a fourth photocurrent induced on the second photodetector in response to the illumination generated by the reference LED. In addition to the induced photocurrents, the LED driver and receiver circuit can measure the forward voltage generated across the first and second photodetectors before, during, or after measuring the induced photocurrents.

[0085] The control circuit can be coupled to the LED driver and receiver circuit, the first and second photodetectors, and the storage medium, and can generally be configured to determine an expected photocurrent value for the phosphor-converted LED from the calibration value table using the forward voltage measured by the LED driver and receiver circuit during operation of the lighting device and the drive current currently applied to the phosphor-converted LED and the reference LED to produce illumination. In addition, the control circuit can be further configured to: if the expected photocurrent value determined by the control circuit for the phosphor-converted LED is different from the photocurrent measured by the LED driver and receiver circuit for the phosphor-converted LED, adjust the drive current currently applied by the LED driver and receiver circuit to the phosphor-converted LED to produce illumination.

[0086] As noted below, for example, the control circuit can calculate scaling factors for the phosphor-converted LED by dividing the expected photocurrent value by the induced photocurrent measured by the LED driver and receiver circuit; apply one of the scaling factors to the desired luminous flux value of the phosphor-converted LED to obtain an adjusted luminous flux value; and adjust the drive current currently applied to the phosphor-converted LED to achieve the adjusted luminous flux value.

[0087] In some embodiments, the control circuitry may determine a first expected photocurrent value for the first portion of the spectrum of the phosphor-converted LED at the first photodetector and a second expected photocurrent value for the second portion of the spectrum of the phosphor-converted LED at the second photodetector. Next, the control circuitry may calculate a first proportionality factor by dividing the first expected photocurrent value determined by the control circuitry by the first photocurrent measured by the LED driver and receiver circuitry. A second proportionality factor may be calculated by dividing the second expected photocurrent value determined by the control circuitry by the second photocurrent measured by the LED driver and receiver circuitry. In some embodiments, the first and second proportionality factors may be used by the control circuitry to account for changes in the luminous flux and chromaticity produced by the phosphor-converted LED over time.

[0088] To compensate for aging-related changes in luminous flux, the control circuit may apply the second scaling factor to the desired luminous flux value of the phosphor-converted LED to obtain an adjusted luminous flux value for the phosphor-converted LED. Next, the control circuit may adjust the drive current currently applied to the phosphor-converted LED to achieve the adjusted luminous flux value. In some embodiments, the control circuit may use the first and second scaling factors to determine how the chromaticity of the phosphor-converted LED changes over time, and may adjust the drive current applied to other emitting LEDs in the lighting device based on this determination to maintain a desired overall chromaticity or color point for the lighting device.

[0089] In some embodiments, the control circuit may compensate for detector aging when adjusting the chromaticity of the phosphor-converted LED. For example, the control circuit may determine a third expected photocurrent value of the reference LED on the first photodetector and a fourth expected photocurrent value of the reference LED on the second photodetector. The third and fourth expected photocurrent values ​​of the reference LED may be determined in the same manner as the first and second expected photocurrent values ​​of the phosphor-converted LED. Next, the control circuit may calculate a third proportionality factor by dividing the third expected photocurrent value determined by the control circuit by the third photocurrent measured by the LED driver and receiver circuit. A fourth proportionality factor may be calculated by dividing the fourth expected photocurrent value determined by the control circuit by the fourth photocurrent measured by the LED driver and receiver circuit. In some embodiments, the control circuit may apply the fourth proportionality factor to the desired luminous flux value of the reference LED to obtain an adjusted luminous flux value of the reference LED. Next, the control circuit may adjust the drive current currently applied to the reference LED to achieve the adjusted luminous flux value.

[0090] In some embodiments, the third and fourth scale factors may be used as a reference to account for aging of the first and second photodetectors. For example, the control circuit may generate a scale factor ratio for the first photodetector by dividing the first scale factor by the third scale factor, and may generate a scale factor ratio for the second photodetector by dividing the second scale factor by the fourth scale factor. Next, the control circuit may divide the scale factor ratio generated for the second photodetector by the scale factor ratio generated for the first photodetector to generate a phosphor-over-LED Ratio for the phosphor-converted LED. The control circuit may then use the phosphor-over-LED ratio generated for the phosphor-converted LED to adjust the chromaticity of the phosphor-converted LED. Once the chromaticity of the phosphor-converted LED is determined, the second scale factor may be applied to the desired luminous flux value of the phosphor-converted LED to account for lumen output changes over time.

[0091] As noted above, methods for calibrating and controlling a lighting device comprising a phosphor-converted LED and at least two different photodetectors are also provided herein. According to one embodiment, a calibration method for calibrating a lighting device comprising a phosphor-converted LED and at least two different photodetectors may be initiated by, after subjecting the phosphor-converted LED to a first ambient temperature, continuously applying at least three different drive currents to the phosphor-converted LED so as to produce illumination at different brightness levels. At each of the at least three different drive currents, the calibration method may measure a photocurrent induced on the first and second photodetectors by the illumination generated by the phosphor-converted LED, and a forward voltage generated across the first and second photodetectors before or after measuring each induced photocurrent. The results of the measuring step may be stored within the lighting device so as to calibrate the phosphor-converted LED at the first ambient temperature.

[0092] As noted above, the photocurrent induced on the first photodetector by the illumination produced by the phosphor-converted LED can correspond to a first portion of the spectrum of the phosphor-converted LED, wherein the first portion (e.g., the LED portion) has a first peak emission wavelength (e.g., about 400 nm to about 500 nm). The photocurrent induced on the second photodetector by the illumination produced by the phosphor-converted LED can correspond to a second portion of the spectrum of the phosphor-converted LED, wherein the second portion (e.g., the phosphor portion) has a second peak emission wavelength that is substantially different from the first peak emission wavelength (e.g., about 500 nm to about 650 nm). By separately measuring the photocurrents induced on the first and second photodetectors by the illumination produced by the phosphor-converted LED, and storing these values ​​within the lighting device, the calibration method enables different portions of the phosphor-converted LED spectrum to be calibrated separately, as if the phosphor-converted LED were two separate LEDs.

[0093] In some embodiments, the calibration method may also obtain separate luminous flux and chromaticity measurements of the first portion and the second portion of the phosphor-converted LED spectrum at each of the at least three different drive currents. By separately measuring the luminous flux and chromaticity attributable to each portion of the phosphor-converted LED spectrum at each of the at least three different drive currents, and storing these values ​​within the lighting device, the calibration method enables separate calibration of different portions of the phosphor-converted LED spectrum as if the phosphor-converted LED were two separate LEDs.

[0094] Once the calibration values ​​described above are obtained for the first ambient temperature, the calibration method can repeat the steps of: applying at least three different drive currents in succession; measuring the photocurrent induced on the first and second photodetectors; and measuring the forward voltage generated across the first and second photodetectors after subjecting the lighting device to a second ambient temperature substantially different from the first ambient temperature. In some embodiments, the luminous flux and chromaticity attributable to each portion of the phosphor-converted LED spectrum can also be obtained for each of the at least three different drive currents at the second temperature. The results of the measuring steps can be stored in the lighting device to calibrate the phosphor-converted LED at the second ambient temperature. In some embodiments, the calibration method can be performed for a reference LED having a peak emission wavelength that falls within the first portion of the spectrum of the phosphor-converted LED.

[0095] According to another embodiment, a compensation method for controlling a lighting device including at least a phosphor-converted LED, a first photodetector, and a second photodetector may include: substantially continuously applying a drive current to the phosphor-converted LED to generate illumination; and measuring photocurrents induced on the first and second photodetectors in response to the illumination generated by the phosphor-converted LED and received by the first and second photodetectors. For example, the compensation method may measure a first photocurrent induced on the first photodetector and a second photocurrent induced on the second photodetector in response to the illumination generated by the phosphor-converted LED. The first photocurrent may correspond to a first portion of the spectrum of the phosphor-converted LED, and the second photocurrent may correspond to a second portion of the spectrum of the phosphor-converted LED. In addition to the induced photocurrent, the compensation method may measure a forward voltage generated across the first and second photodetectors by applying a non-operating drive current to each of the first and second photodetectors before or after measuring the induced photocurrent.

[0096] Once the induced photocurrent and forward voltage are obtained from the first and second photodetectors, the compensation method can determine an expected photocurrent value of the phosphor-converted LED corresponding to the forward voltage measured across the first and second photodetectors and the drive current currently applied to the phosphor-converted LED by applying one or more interpolation techniques to a stored calibration value table that relates the forward voltage and photocurrent to the drive current at multiple different temperatures. In addition, if there is a difference between the expected photocurrent value and the measured photocurrent, the compensation method can adjust the drive current currently applied to the phosphor-converted LED.

[0097] Specifically, the compensation method can determine a first expected photocurrent value for a first portion of the spectrum of the phosphor-converted LED on the first photodetector and a second expected photocurrent value for a second portion of the spectrum of the phosphor-converted LED on the second photodetector. Next, the compensation method can calculate a first proportionality factor by dividing the first expected photocurrent value by the first photocurrent induced on the first photodetector in the measuring step. The compensation method can calculate a second proportionality factor by dividing the second expected photocurrent value by the second photocurrent induced on the second photodetector in the measuring step. As noted above, the first and second proportionality factors can be used by the compensation method to account for changes in the luminous flux and chromaticity produced by the phosphor-converted LED over time.

[0098] To compensate for aging-related changes in luminous flux, the compensation method may apply a second scaling factor to a desired luminous flux value of the phosphor-converted LED to obtain an adjusted luminous flux value of the phosphor-converted LED. Next, the compensation method may adjust a drive current currently applied to the phosphor-converted LED to achieve the adjusted luminous flux value. In some embodiments, the compensation method may use the first and second scaling factors to determine how the chromaticity of the phosphor-converted LED changes over time. Based on this determination, the compensation method may adjust the drive current applied to other emitting LEDs in the lighting device to maintain a desired overall chromaticity or color point of the lighting device.

[0099] In some embodiments, the compensation method may use a reference LED to perform steps similar to those described above. For example, the compensation method may substantially continuously apply a drive current to the reference LED to generate illumination; and measure the photocurrent induced on the first and second photodetectors in response to the illumination generated by the reference LED and received by the first and second photodetectors. Specifically, the compensation method may measure a third photocurrent induced on the first photodetector and a fourth photocurrent induced on the second photodetector in response to the illumination generated by the reference LED. Next, the compensation method may determine an expected photocurrent value of the reference LED corresponding to the forward voltage measured across the first and second photodetectors and the drive current currently applied to the reference LED by applying one or more interpolation techniques to a stored calibration value table that relates forward voltage and photocurrent to the drive current at multiple different temperatures.

[0100] Specifically, the compensation method may determine a third expected photocurrent value of the reference LED on the first photodetector and a fourth expected photocurrent value of the reference LED on the second photodetector. Next, the compensation method may calculate a third proportionality factor by dividing the third expected photocurrent value by the third photocurrent induced on the first photodetector in the measuring step; and calculate a fourth proportionality factor by dividing the fourth expected photocurrent value by the fourth photocurrent induced on the second photodetector in the measuring step. In some embodiments, the compensation method may apply the fourth proportionality factor to the desired luminous flux value of the reference LED to obtain an adjusted luminous flux value of the reference LED; and may adjust the drive current currently applied to the reference LED to achieve the adjusted luminous flux value.

[0101] In some embodiments, the third and fourth scale factors generated for the reference LED can be used as a reference to account for the aging of the first and second photodetectors. For example, the compensation method can generate a scale factor ratio for the first photodetector by dividing the first scale factor by the third scale factor, and can generate a scale factor ratio for the second photodetector by dividing the second scale factor by the fourth scale factor. Next, the method can divide the scale factor ratio generated for the second photodetector by the scale factor ratio generated for the first photodetector to generate a phosphor-to-LED ratio for the phosphor-converted LED. The method can then use the phosphor-to-LED ratio to adjust the chromaticity of the phosphor-converted LED. Once the chromaticity of the phosphor-converted LED is determined, the second scale factor can be applied to the expected luminous flux value of the phosphor-converted LED to account for changes in lumen output over time.

[0102] Various embodiments of improved emitter modules for light emitting diode (LED) lighting devices are also provided herein. Generally, the improved emitter modules disclosed herein can utilize a single layer substrate or a multi-layer substrate designed to improve thermal separation between emission LEDs and between emission LEDs and photodetectors while also providing good thermal conductivity to a heat sink. The multi-layer substrate further includes multiple routing layers and dielectric layers, which provide enhanced routing flexibility for connecting emission LED chains together and electrically isolating the emission LEDs and photodetectors from the heat sink.

[0103] According to one embodiment, a lighting device including one or more emitter modules is provided herein, wherein each emitter module generally includes: a plurality of emitting LEDs, the plurality of emitting LEDs being configured to generate illumination for the lighting device; and one or more photodetectors, the one or more photodetectors being configured to detect the illumination generated by the plurality of LEDs. Typically, the plurality of LEDs and the one or more photodetectors are mounted on a substrate and enclosed within a primary optical structure. A heat sink is coupled to a bottom surface of the substrate for dissipating heat generated by the emitter module.

[0104] The emitter module can include essentially any number and color of emission LEDs and essentially any number and color of photodetectors. In an exemplary embodiment, the emission LEDs include one or more red LEDs, one or more blue LEDs, one or more green LEDs, and one or more white or yellow LEDs. The emission LEDs can generally be arranged in an array near the center of the main optical structure, and the one or more photodetectors can generally be arranged near the periphery of the array. In an exemplary embodiment, the one or more photodetectors can include one or more red, orange, yellow and / or green LEDs. In some embodiments, if one or more of the emission LEDs are sometimes configured to detect incident light, then the one or more photodetectors can be omitted.

[0105] The primary optical structure can be formed from a variety of different materials and can have essentially any shape and / or size necessary to shape the light emitted by the emitting LED in a desired manner. In some embodiments, the primary optical structure can have a dome shape. However, those skilled in the art will understand how the primary optical structure can have essentially any other shape or configuration that encapsulates the emitting LED and one or more photodetectors. In some embodiments, the shape, size, and material of the dome can generally be designed to improve optical efficiency and color mixing within the emitter module.

[0106] The heat sink is coupled to the bottom surface of the substrate for directing heat away from the heat generating components of the transmitter module. Typically, the heat sink can include substantially any material having relatively high thermal and electrical conductivity. In some embodiments, the heat sink is formed of a material having a thermal conductivity range between about 200W / (mK) and about 400W / (mK). In one embodiment, the heat sink is formed of a copper or copper alloy material, or an aluminum or aluminum alloy material. In some embodiments, the heat sink can be a relatively thick layer ranging between about 1mm and about 10mm, and in one embodiment, can be about 3mm thick.

[0107] The substrate is typically configured to provide a relatively high thermal impedance in the lateral direction and a relatively low thermal impedance in the vertical direction. In one embodiment, the substrate is formed so as to include only a single material layer. In order to provide a relatively high thermal impedance in the lateral direction, the single-layer substrate may be formed of a material having a relatively high thermal impedance or a relatively low thermal conductivity. In one example, the substrate may be formed of a material having a thermal conductivity of less than about 150 W / (mK) (e.g., aluminum nitride), a material having a thermal conductivity of less than about 30 W / (mK) (e.g., aluminum oxide), or a material having a thermal conductivity of less than about 1 W / (mK) (e.g., PTFE or other laminated materials).

[0108] Typically, a single layer substrate can provide a relatively low thermal impedance in the vertical direction by providing a relatively low thermal impedance path between each of the emitting LEDs and each of the one or more photodetectors and a heat sink. In some embodiments, the low thermal impedance path can be implemented by minimizing the thickness of the substrate and using a plurality of thermally conductive wires to connect each of the LEDs and each of the one or more photodetectors to a heat sink. For example, the thickness of the substrate can range between about 300 μm and about 500 μm.

[0109] The plurality of heat-conducting wires may include substantially any heat-conducting material. In some embodiments, the heat-conducting wire may be formed of a material having a thermal conductivity range between about 200 W / (mK) and about 400 W / (mK). The material used for the heat-conducting wire may be the same as or different from the material used for the heat sink. In one embodiment, the heat-conducting wire is formed of aluminum, an aluminum alloy, copper, or a copper alloy material. The plurality of heat-conducting wires may be formed by drilling vertical holes through the substrate (using mechanical or optical means) and using any appropriate method to fill or plate the holes (or through-holes) with a metal material. In some embodiments, each heat-conducting wire may include a plurality (e.g., about 10 to 20) dense through-holes, each of which is only a few hundred microns wide.

[0110] Although a single layer substrate provides desirable thermal properties (e.g., good thermal separation between the emitting LED and the photodetector, and good thermal conductivity to the heat sink), it cannot provide the thermal properties desired in some emitter modules. In order to provide routing flexibility and electrical isolation between the emitting LED and the photodetector and the heat sink, a preferred embodiment of the present invention may utilize a multi-layer substrate.

[0111] According to one embodiment, the multilayer substrate may include a first routing layer, a first dielectric layer, a second routing layer, and a second dielectric layer. The first routing layer may be coupled to electrical contacts of the emitting LED and the one or more photodetectors, and may be formed on the first dielectric layer. In some cases, the first routing layer may have a thickness ranging from about 10 μm to about 20 μm, and may be formed of a material having a thermal conductivity ranging from 200 W / (mK) to about 400 W / (mK) (e.g., copper or aluminum material, or alloys thereof).

[0112] The first dielectric layer is coupled to the bottom surface of the first routing layer and sandwiched between the first routing layer and the second routing layer for electrically isolating the electrical contacts of the emitting LED and the photodetector from the heat sink. In some embodiments, the first dielectric layer can be a relatively thin layer having a thickness between about 10 μm and about 100 μm, and can be formed of a dielectric material having a relative dielectric constant ranging between about 3 and 12. In one example, the first dielectric layer can be formed of an aluminum nitride material or an aluminum oxide material, but is not limited to such materials.

[0113] In addition to providing electrical isolation, the first dielectric layer provides relatively high thermal impedance in the lateral direction by using a relatively low thermal conductivity (which is less than about 150 W / (mK)) and keeping the thickness of the layer small relative to the spacing between the emitting LED and the photodetector. In an exemplary embodiment, the first dielectric layer can have a thickness of about 30 μm and can separate the emitting LED and the photodetector by at least 200 to 300 μm on the upper surface of the multilayer substrate. Such an embodiment will provide a thermal conductivity in the vertical direction that is at least 10 times higher than the thermal conductivity provided in the lateral direction.

[0114] The second routing layer is coupled between the first dielectric layer and the second dielectric layer, and is generally configured to route signals between the first routing layer and external electrical contacts arranged outside the main optical structure. Like the first routing layer, the second routing layer can have a thickness ranging from about 10 μm to about 20 μm, and can be formed of a material having a thermal conductivity ranging from 200 W / (mK) to about 400 W / (mK) (e.g., copper or aluminum materials, or alloys thereof). In some embodiments, vias can be formed in the first dielectric layer to route signals between the first routing layer and the second routing layer. These vias can be formed according to any known process.

[0115] In some embodiments, the second dielectric layer can be coupled between the second routing layer and the heat sink. In other embodiments, the third routing layer can be coupled between the second dielectric layer and the heat sink. Unlike the first and second routing layers (which include metal lines printed on the first and second dielectric layers), the third routing layer can extend substantially continuously across the upper surface of the heat sink to improve thermal contact between the plurality of thermally conductive lines and the heat sink and improve heat dissipation thereon.

[0116] Like the first dielectric layer, the second dielectric layer can be configured to provide a relatively high thermal impedance in the lateral direction by using a material with a relatively low thermal conductivity. For example, the second dielectric layer can be made of a ceramic material (e.g., aluminum nitride) with a thermal conductivity less than about 150W / (mK), or a ceramic material (e.g., aluminum oxide) with a thermal conductivity less than about 30W / (mK). However, the first and second dielectric layers are not limited to ceramic materials or valorized dielectric materials. In some embodiments, laminated materials such as printed circuit board (PCB) FR4 or metal-clad PCB materials can be used to form these layers. However, because the thermal conductivity of the laminated material (e.g., less than about 1W / (mK)) is much smaller than the thermal conductivity of the ceramic material, using the laminated material instead of the ceramic material will reduce the thermal conductivity of the second dielectric layer.

[0117] Unlike the first dielectric layer (which is relatively thin), the second dielectric layer provides stiffness to the transmitter module by utilizing a relatively thick layer (e.g., about 100 μm and about 1000 μm). In addition, the second dielectric layer includes a plurality of thermally conductive wires extending vertically through the second dielectric layer between the second routing layer and the heat sink to increase thermal conductivity in the vertical direction.

[0118] As noted above, the plurality of thermally conductive wires may be formed of a material having a thermal conductivity ranging between about 200 W / (mK) and about 400 W / (mK), such as copper or aluminum materials or alloys thereof, and may be formed by drilling vertical holes through the second dielectric layer (using mechanical or optical means) and using any appropriate method to fill or plate the holes (or through-holes) with appropriate metal materials. In some embodiments, each thermally conductive wire may include a plurality (e.g., about 10 to 20) dense through-holes, each of which is several hundred microns wide. In some embodiments, thermal conductivity may be further increased in the vertical direction by increasing the number of thermally conductive wires included below the emitting LEDs. While this approach will provide better overall thermal conductivity from the LED array to the heat sink, it will provide poorer thermal separation between the emitting LEDs. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Other objects and advantages of the present invention will become apparent after reading the following detailed description and after referring to the accompanying drawings.

[0120] Figure 1 is a graphical representation of the 1931 CIE Chromaticity Diagram showing the color gamut of human color perception and the color gamut achievable by a lighting device including multiple multi-color LEDs (e.g., red, green, and blue);

[0121] Figure 2 is a diagram showing the nonlinear relationship between the relative luminous flux and junction temperature of white, blue, and green LEDs;

[0122] Figure 3 is a graphical representation showing the substantially more nonlinear relationship between the relative luminous flux and junction temperature of red, orange-red, and yellow (amber) LEDs;

[0123] Figure 4 is a diagram showing the nonlinear relationship between the relative luminous flux and driving current of red and orange-red LEDs;

[0124] Figure 5 is a graphical representation showing a substantially more nonlinear relationship between the relative luminous flux and drive current of white, blue, and green LEDs;

[0125] Figure 6 is a flow chart of an improved method for calibrating a lighting device including a plurality of LEDs and one or more photodetectors according to one embodiment of the present invention;

[0126] Figure 7 is a diagram showing how Figure 6 An exemplary calibration value table is obtained and stored in a lighting device by a calibration method;

[0127] Figure 8 is a flow chart of an improved compensation method according to an embodiment of the present invention;

[0128] Fig. 9 is an exemplary timing diagram for a lighting device including four emitting LEDs, illustrating periodic intervals at which measurements (e.g., emitter forward voltage) are obtained from each emitting LED (one LED at a time);

[0129] Fig.10 is a graphical representation that depicts Figure 8 How can one or more interpolation techniques be used in the compensation method? Figure 6 The drive current required to produce a desired luminous flux for a given LED is determined using a calibration value obtained during a calibration method and stored in the lighting device;

[0130] Fig.11 is a graphical representation that depicts Figure 8 How can one or more interpolation techniques be used in the compensation method, using the current forward voltage, the current drive current and the Figure 6 The expected x chromaticity value of a certain LED is determined using a calibration value obtained during a calibration method and stored in the lighting device;

[0131] Fig.12 is a graphical representation that depicts Figure 8 How can one or more interpolation techniques be used in the compensation method, using the current forward voltage, the current drive current and the Figure 6The expected y chromaticity value of a certain LED is determined using a calibration value obtained during a calibration method and stored in the lighting device;

[0132] Fig.13 is a flow chart of an improved compensation method according to another embodiment of the present invention;

[0133] Fig.14 is an exemplary timing diagram for a lighting device including four emitting LEDs, illustrating periodic intervals for obtaining (one LED at a time) measurements from one or more photodetectors (e.g., sensing photocurrent and detector forward voltage) and from each emitting LED (e.g., emitter forward voltage);

[0134] Fig.15 is a graphical representation that depicts Fig.13 How can one or more interpolation techniques be used in the compensation method, using the current forward voltage, the current drive current and the Figure 6 The expected photocurrent value of a certain LED is determined using a calibration value obtained during the calibration method and stored in the lighting device;

[0135] Fig.16A are photographs of exemplary lighting equipment;

[0136] Fig. 16B is a computer-generated image showing what may be included in Fig.16A a top view of an exemplary emitter module within an exemplary lighting device of;

[0137] Fig.17A is a photo of another exemplary lighting device;

[0138] Fig. 17B is a computer-generated image showing what may be included in Fig.17A a top view of an exemplary emitter module within an exemplary lighting device of;

[0139] Fig.18A is a side view of an improved transmitter module according to one embodiment of the present invention;

[0140] Fig.18B is a side view of an improved transmitter module according to another embodiment of the present invention;

[0141] Fig.19 is an exemplary block diagram of circuit components that may be included in a lighting device according to one embodiment of the present invention;

[0142] Fig. 20 According to one embodiment of the present invention, it may include Fig.19 An exemplary block diagram of an LED driver and receiver circuit within a lighting device of FIG. 1 ; and

[0143] Fig.21 is an exemplary diagram depicting how the spectrum of a phosphor-converted LED can be split into two parts, and showing how the phosphor efficiency decreases as the phosphor ages.

[0144] Although the present invention is susceptible to various modifications and alternative forms, specific embodiments of the invention are shown by way of example in the drawings and will be described in more detail herein. However, it should be understood that the drawings and detailed description thereof are not intended to limit the invention to the specific forms disclosed, but on the contrary, the invention will cover all modifications, equivalents and alternative forms falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION

[0145] LEDs typically include a chip composed of semiconductor materials doped with impurities to create a pn junction. As in other diodes, current flows easily from the p-side or anode to the n-side or cathode, rather than in the opposite direction. Charge carriers (electrons or holes) flow into the junction from electrodes with different voltages. When an electron encounters a hole, it falls to a lower energy level and releases energy in the form of a photon (i.e., light). The wavelength of light emitted by an LED, and therefore its color, depends on the bandgap energy of the material forming the pn junction of the LED.

[0146] Red and yellow LEDs typically include materials with relatively low bandgap energies (e.g., AlInGaP) and thereby produce longer wavelengths of light. For example, the peak wavelengths of most red and yellow LEDs are in the range of about 610 to 650 nm and about 580 to 600 nm, respectively. On the other hand, green and blue LEDs typically include materials with larger bandgap energies (e.g., GaN or InGaN) and thereby produce shorter wavelengths of light. For example, the peak wavelengths of most green and blue LEDs are in the range of about 515 to 550 nm and about 450 to 490 nm, respectively.

[0147] In some cases, a "white" LED can be formed by covering or coating, for example, a green LED having a peak emission wavelength of about 450 to 490 nm or a longer peak emission wavelength (e.g., about 525 nm to about 600 nm) with a phosphor (e.g., YAG) that down-converts photons emitted by the green LED to a lower energy level. In some cases, such an LED can be configured to produce substantially white light having a correlated color temperature (CCT) of about 3000 K. However, a skilled artisan will understand how different colored LEDs and / or different phosphors can be used to produce a "white" LED having a potentially different CCT.

[0148] When two or more different color LEDs are combined into a single package, the spectral content of the individual LEDs is combined to produce mixed light. In some cases, different color LEDs can be combined to produce white light or near-white light in a wide color gamut of color points or CCTs ranging from "warm white" (e.g., approximately 2600K to 3000K) to "neutral white" (e.g., 3000K to 4000K) to "cool white" (e.g., 4000K to 8300K). Examples of white light luminaires include, but are not limited to, white light luminaires that combine red, green, and blue (RGB) LEDs; red, green, blue, and yellow (RGBY) LEDs; white and red (WR) LEDs and RGBW LEDs.

[0149] The present invention generally relates to lighting devices having a plurality of light emitting diodes (LEDs) and one or more photodetectors. For simplicity, throughout this disclosure, the term "LED" will be used to refer to a single LED or a chain of LEDs connected in series supplied with the same drive current. According to one embodiment, the present invention provides an improved method for calibrating and stepping individual LEDs within an LED lighting device so as to accurately maintain a desired luminous flux and a desired chromaticity of the lighting device as the drive current, temperature and / or time vary.

[0150] Although not limited thereto, because the output characteristics of different color LEDs vary in different ways with drive current, temperature and time, the present invention is particularly suitable for such lighting devices (i.e., multi-color lighting devices) in which two or more different color LEDs are combined to produce mixed white light or near-white light. Because changes in drive current inherently affect the lumen output, color and temperature of the lighting device, the present invention is also particularly suitable for such lighting devices (i.e., adjustable lighting devices): the lighting device enables the target dimming level and / or target chromaticity setting to be changed by adjusting the drive current supplied to one or more of the LEDs.

[0151] Figure 2 and Figure 3 shows how the relative luminous flux of individual LEDs varies with junction temperature for different color LEDs. Figure 2 and Figure 3 As shown in , the luminous flux output from all LEDs generally decreases with increasing temperature. For some colors (e.g., white, blue, and green), the relationship between luminous flux and junction temperature is relatively linear (see Figure 2 ), while for other colors (e.g., red, orange, and especially yellow), the relationship is significantly nonlinear (see Figure 3). The chromaticity of an LED also changes with temperature due to a shift in the dominant wavelength (for both phosphor-converted and non-phosphor-converted LEDs) and changes in phosphor efficiency (for phosphor-converted LEDs). In general, the peak emission wavelength of a green LED tends to decrease with increasing temperature, while the peak emission wavelengths of red and green LEDs tend to increase with increasing temperature. While the change in chromaticity with respect to temperature is relatively linear for most colors, red and yellow LEDs tend to exhibit more significant nonlinear changes.

[0152] As LEDs age, the luminous flux output from both phosphor-converted and non-phosphor-converted LEDs, as well as the chromaticity of the phosphor-converted LEDs, also changes over time. Early in the life, the luminous flux may be able to increase (become brighter) or decrease (become dimmer), while later in the life, the luminous flux generally decreases. As expected, lumen output decreases faster over time when the LED is subjected to higher drive currents and higher temperatures. As phosphor-converted LEDs age, the phosphor efficiency becomes lower and the amount of green light that passes through the phosphor increases. This reduction in phosphor efficiency makes the overall color produced by the phosphor-converted LED appear "colder" over time. Although the dominant wavelength and chromaticity of non-phosphor-converted LEDs do not change over time, the luminous flux decreases as the LED ages, which actually causes the chromaticity of multi-color LED lighting devices to change over time.

[0153] When different colored LEDs are combined into a multi-color lighting device, the color point of the resulting device often changes significantly with changes in temperature and over time. For example, when red, green, and blue LEDs are combined into a white light lighting device, the color point of the device may appear increasingly "colder" as the temperature increases. This is because the luminous flux produced by the red LED decreases significantly with increasing temperature, while the luminous flux produced by the green and blue LEDs remains relatively stable (see Figure 2 and Figure 3 ).

[0154] To account for temperature and aging effects, some prior art lighting devices attempt to maintain consistent lumen output and / or consistent chromaticity over temperature and time by measuring characteristics of the emitting LEDs and increasing the drive current supplied to one or more of the emitting LEDs. For example, some prior art lighting devices measure the temperature of the lighting device (either directly through an ambient temperature sensor or heat sink, or directly through forward voltage measurement) and adjust the drive current supplied to one or more of the emitting LEDs to account for temperature-related lumen output changes. Other prior art lighting devices measure the lumen output from individual emitting LEDs and, if the measured value differs from a target value, increase the drive current supplied to the emitting LED to account for changes in luminous flux that occur over time.

[0155] However, varying the drive current supplied to the emitting LED inherently affects the luminous flux and chromaticity produced by the LED lighting device. Figure 4 and Figure 5 The relationship between luminous flux and drive current is shown for different color LEDs (e.g., red, orange-red, white, blue, and green LEDs). In general, luminous flux increases with higher drive current and decreases with lower drive current. However, the variation of luminous flux with drive current is nonlinear for all color LEDs, and for some color LEDs (e.g., blue and green LEDs), this nonlinear relationship is substantially more pronounced than for others. Because higher drive currents inherently result in higher LED junction temperatures (see Figure 2 and Figure 3 ), so as the drive current increases, the chromaticity of the illumination also changes to counteract temperature and / or aging effects. While the change in chromaticity with current / temperature is relatively linear for all color LEDs, the rate of change is different for different LED colors and may even vary from one part to another.

[0156] Although some prior art lighting devices can adjust the drive current supplied to the emitting LED, these devices cannot provide accurate temperature and aging compensation because they cannot account for the nonlinear relationship between the luminous flux and the junction temperature of certain color LEDs ( Figure 2 and Figure 3 ), the nonlinear relationship between the luminous flux and driving current of all color LEDs ( Figure 4 and Figure 5 ), and the fact that these relationships are different for different color LEDs. These devices also fail to account for the fact that the rate at which chromaticity changes with drive current / temperature is different for different color LEDs. Without accounting for these behaviors, prior art lighting devices are unable to provide accurate temperature and aging compensation for all LEDs included in a multi-color LED lighting device.

[0157] There remains a need for improved lighting devices and improved methods for calibrating and compensating individual LEDs included in LED lighting devices to maintain a desired luminous flux and a desired chromaticity over time with changes in drive current, temperature, and as the LEDs age. This need is particularly relevant to multi-color LED lighting devices because different LED colors respond differently over temperature and time, and to lighting devices that provide dimming and / or color adjustment capabilities because changes in drive current inherently affect the lumen output, color, and temperature of the lighting device.

[0158] To meet these needs, an improved lighting device and an improved method for individually calibrating and compensating each LED used in an LED lighting device are provided herein. The improved calibration and compensation method described herein overcomes the shortcomings of conventional methods, which cannot provide accurate temperature and aging compensation for all LEDs included in an LED lighting device.

[0159] Exemplary embodiment of an improved method for calibrating a lighting device

[0160] Figure 6 An embodiment of an improved method for calibrating a lighting device including a plurality of LEDs and at least one dedicated photodetector is presented. In some embodiments, Figure 6 The calibration method shown in can be used to calibrate a lighting device having LEDs (all of which have the same color). However, because the output characteristics of LEDs of different colors vary in different ways with drive current, temperature, and time, the calibration method described herein is particularly suitable for calibrating a lighting device that includes two or more LEDs of different colors (i.e., a multi-color LED lighting device). Because changes in drive current inherently affect the lumen output, color, and temperature of a lighting device, the calibration method described herein is also particularly suitable for calibrating a lighting device that provides dimming and / or color adjustment capabilities (i.e., an adjustable LED lighting device).

[0161] 16 to 16 Fig. 20While describing an exemplary embodiment of an improved lighting device, the figure shows different types of LED lighting devices, each of which has one or more emitter modules. As described below, each emitter module can generally include a plurality of emission LEDs arranged in an array, and at least one dedicated photodetector spaced apart about the periphery of the array. In an exemplary embodiment, the emission LED array can include red, green, blue and white (or yellow) LEDs, and the at least one dedicated photodetector can include one or more red, orange, yellow and / or green LEDs. However, the present invention is not limited to any particular color, quantity, combination or arrangement of emission LEDs or photodetectors. A skilled artisan will understand how the method steps described herein can be applied to other LED lighting devices having substantially different emitter modules.

[0162] As in Figure 6 As shown in , the improved calibration method can generally begin by subjecting the lighting device to a first ambient temperature (in step 10). Once subjected to this temperature, a plurality of different drive current levels can be applied to the emitting LED (in step 12), and a plurality of measurements can be obtained from both the emitting LED and the dedicated photodetector (in steps 14 and 16) at each of the different drive current levels. Specifically, two or more different drive current levels can be applied to each emitting LED in succession, one LED at a time, for the purpose of obtaining measurements from the lighting device. These measurements can generally include optical measurements and electrical measurements.

[0163] For example, a plurality of optical measurements may be obtained (in step 14) from the illumination produced by each emitting LED at each of the different drive current levels. According to one embodiment, the optical measurements may include a plurality of luminous flux, x-chromaticity, and y-chromaticity measurements, obtained for each emitting LED at two or more different drive current levels. However, the optical measurements described herein are not limited to luminous flux, x-chromaticity, and y-chromaticity, and may include additional or alternative optical measurements in other embodiments of the invention.

[0164] In general, the chromaticity calibration values ​​described herein may correspond to the CIE 1931 XYZ color space, the CIE 1931 RGB color space, the CIE 1976 LUV color space, or various other RGB color spaces (e.g., sRGB, Adobe RGB, etc.). Although the calibration and compensation methods described herein may only obtain and utilize x and y chromaticity calibration values, those skilled in the art will understand how to alternatively obtain chromaticity values ​​from other color spaces and how to use them in the methods described herein. As such, the calibration and compensation methods described herein and in the claims are considered to include chromaticity calibration values ​​from any color space that can be used to describe the color gamut of an LED lighting device that substantially includes any combination of emitting LEDs as described herein.

[0165] In a preferred embodiment, Figure 7 Three luminous flux (Luma) measurements, three x chromaticity (x chromaticity) measurements, and three y chromaticity (y chromaticity) measurements are measured from each emitting LED at approximately the maximum drive current levels shown in and discussed below (typically about 500 mA, depending on the LED part number and manufacturer), approximately 30% of the maximum drive current, and approximately 10% of the maximum drive current. In some embodiments, an external calibration tool such as a spectrophotometer can be used to obtain luminous flux and x, y chromaticity measurements from the emitting LEDs. In some embodiments, as described below with respect to Fig.19 As described in more detail, measurements obtained from an external calibration tool may be wirelessly transmitted to the lighting device.

[0166] In addition, multiple electrical measurements can be obtained from each of the emitting LEDs and each of the dedicated photodetectors at each of the different drive current levels (in step 16). These electrical measurements can include, but are not limited to, photocurrents induced on the dedicated photodetectors and forward voltages measured across the dedicated photodetectors and / or the emitting LEDs. Unlike the optical measurements described above, electrical measurements can be obtained from the dedicated photodetectors and emitting LEDs using LED drivers and receiver circuits included in the lighting device. Fig.19 and Fig. 20 An exemplary embodiment of such a circuit is shown in FIG. 1 and described in more detail below.

[0167] At each of the different drive current levels, the LED driver and receiver circuit measures the photocurrent induced on the dedicated photodetector by the illumination generated by each emitting LED individually. In a preferred embodiment, three photocurrent (Iph_d1) measurements can be obtained from the dedicated photodetector of each emitting LED when the emitting LED is continuously driven to generate illumination at at least three different drive current levels (e.g., 100%, 30%, and 10% of the maximum drive level). In some embodiments, the LED driver and receiver circuit can obtain the photocurrent (Iph_d1) measurements substantially while an external calibration tool is measuring the luminous flux and x and y chromaticity of the illumination generated by the emitting LED at each of the different drive current levels.

[0168] Typically, the drive current applied to the emitting LEDs for measuring luminous flux, chromaticity, and induced photocurrent can be an operating drive current level (e.g., about 20 mA to about 500 mA). In some cases, increasingly larger drive current levels can be applied successively to each of the emitting LEDs in order to obtain the measurements described herein. In other cases, the measurements can be obtained after successively applying gradually decreasing drive current levels to the emitting LEDs. The order in which the drive current levels are applied is largely unimportant, provided that the drive currents are different from one another.

[0169] Although examples are provided herein, the present invention is not limited to any particular value or number of drive current levels, and substantially any value and any number of drive current levels within a range of operating current levels for the LED may be applied to the emitting LED. However, it is generally desirable to obtain luminous flux and chromaticity measurements from the emitting LED, and to obtain photocurrent measurements from the photodetector at a sufficient number of different drive current levels so that the nonlinear relationship between these measurements and the drive current can be accurately characterized across the range of operating current levels for the LED.

[0170] While increasing the number of measurements does improve the accuracy used to characterize nonlinear relationships, it also increases calibration time and cost. While the increase in calibration time and cost is not warranted in all cases, it can be beneficial in some cases. For example, additional luminous flux measurements may be beneficial when trying to characterize the luminous flux versus drive current relationship of certain color LEDs (e.g., blue and green LEDs), which tend to exhibit significantly more nonlinear relationships than other color LEDs (see Figure 4 and Figure 5 ). Thus, a balance should be struck between accuracy and calibration time / cost when selecting a desired number of drive current levels for obtaining measurements of a particular color LED.

[0171] Because increasing the drive current affects the junction temperature of the emission LED, the forward voltage can be measured across each emission LED and each photodetector immediately after each operating drive current level is applied to the emission LED (in step 16). For each operating drive current level, the forward voltage can be measured across each emission LED and each photodetector before or after obtaining the photocurrent measurement result for that operating drive current level. However, unlike the optical measurement result, a relatively small drive current is applied to the emission LED and (multiple) dedicated photodetectors in order to measure the forward voltage generated across them.

[0172] In a preferred embodiment, immediately after applying each of the different drive current levels (e.g., 100%, 30%, and 10% of the maximum drive level) to the emission LED to measure luminous flux, x-chromaticity, and y-chromaticity, three forward voltage (Vfe) measurements can be obtained from each emission LED and three forward voltage (Vfd1) measurements can be obtained from each dedicated photodetector (in step 16). The forward voltage (Vfe and Vfd1) measurements can be obtained at each of the different drive current levels before or after measuring the induced photocurrent (Iph_d1). By measuring the forward voltage (Vfe) across each emission LED and the forward voltage (Vfd1) across each dedicated photodetector immediately after applying each operating drive current level to the emission LED, the Vfe and Vfd1 measurements can be used to provide a good indication of how the junction temperature of the emission LED and the dedicated photodetector changes with changes in the drive current.

[0173] When making forward voltage measurements, a relatively small drive current is supplied to each of the emitting LEDs and each of the dedicated photodetector LEDs, one LED at a time, so that the forward voltage (Vfe or Vfd1) generated across the anode and cathode of the individual LEDs can be measured (in step 16). When making these measurements, all other emitting LEDs in the lighting device are preferably "off" in order to avoid inaccurate forward voltage measurements (because light from other emitting LEDs will induce additional photocurrent in the LED being measured).

[0174] As used herein, a "relatively small drive current" may be broadly defined as a non-operating drive current, or a drive current level that is insufficient to produce significant illumination of the LED. Most LED device manufacturers that use forward voltage measurements to compensate for temperature variations supply the LED with a relatively large drive current (e.g., an operating drive current level sufficient to produce illumination of the LED). Unfortunately, the forward voltage measured at the operating drive current level tends to vary significantly over the life of the LED. As the LED ages, the parasitic resistance within the junction increases, which in turn causes the forward voltage measured at the operating current level to increase over time (regardless of temperature). For this reason, a relatively small (i.e., non-operating) drive current is used herein to limit the resistive portion of the forward voltage drop when obtaining the forward voltage measurement.

[0175] For some common types of emitting LEDs having a one square millimeter junction area, the optimal drive current for obtaining forward voltage measurements from the emitting LED herein may be approximately 0.1 to 10 mA, and more preferably may be approximately 0.3 to 3 mA. In one embodiment, the optimal drive current level for obtaining forward voltage measurements from the emitting LED may be 1 mA. However, smaller / larger LEDs may use proportionally less / more current to keep the current density approximately the same. In embodiments where significantly smaller LEDs are used as dedicated photodetectors, the optimal drive current level for obtaining forward voltage measurements from a single photodetector may range from approximately 100 μA to approximately 300 μA. In one embodiment, the optimal drive current level for obtaining forward voltage measurements from multiple dedicated photodetectors connected in parallel may be approximately 1 mA. The relatively small non-operating drive current (e.g., about 0.3 mA to about 3 mA) used to obtain forward voltage measurements from the emitting LED and the relatively small non-operating drive current (e.g., about 100 μA to about 300 μA) used to obtain forward voltage measurements from a dedicated photodetector are substantially less than the operating drive current levels (e.g., about 20 mA to about 500 mA) used to measure luminous flux, chromaticity, and induced photocurrent in steps 14 and 16.

[0176] After obtaining the measurements described in steps 14-16 at the first temperature, the lighting device is subjected to a second ambient temperature substantially different from the first ambient temperature (in step 18). Once subjected to this second temperature, steps 12-16 are repeated (in step 20) to obtain an additional plurality of optical measurements from each of the emitting LEDs (in step 14) and an additional plurality of electrical measurements from the emitting LEDs and the dedicated photodetector (in step 16). The additional measurements may be obtained at the second ambient temperature in the same manner as described above for the first ambient temperature.

[0177] In one embodiment, the second ambient temperature may be substantially less than the first ambient temperature. For example, the second ambient temperature may be approximately equal to room temperature (e.g., approximately 25° C.), and the first ambient temperature may be substantially greater than room temperature. In one example, the first ambient temperature may be closer to an elevated temperature (e.g., approximately 70° C.) or a maximum temperature (e.g., approximately 85° C.) at which the device is expected to operate. In an alternative embodiment, the second ambient temperature may be substantially greater than the first ambient temperature.

[0178] It is worth noting that the exact values, number, and order of temperatures applied to calibrate individual LEDs are somewhat unimportant. However, it is generally desirable to obtain luminous flux, x and y chromaticity, and photocurrent calibration values ​​at many different temperatures so that the nonlinear relationship between these measurements and the drive current can be accurately characterized across the operating temperature range of the LEDs. In a preferred embodiment, the lighting device can be subjected to two substantially different ambient temperatures selected from the operating temperature range of the lighting device. Although it is possible to obtain the measurements described herein at three (or more) temperatures, doing so may add significant expense, complexity, and / or time to the calibration process. For this reason, it is generally preferred to calibrate the emitting LED and (multiple) dedicated photodetectors at only two different temperatures (e.g., about 25°C and about 70°C).

[0179] In some embodiments, the lighting device may be subjected to the first and second ambient temperatures by artificially generating the temperatures during the calibration process. However, it is generally preferred that the first and second ambient temperatures are ambient temperatures that occur naturally during production of the lighting device, as this simplifies the calibration process and greatly reduces the costs associated therewith. In one embodiment, measurements obtained at elevated temperatures may be obtained after LED aging when the lighting device is relatively hot (e.g., approximately 50°C to 85°C), and at some time thereafter (e.g., at the end of a production line), a room temperature calibration may be performed to obtain measurements when the lighting device is relatively cool (e.g., approximately 20°C to 30°C).

[0180] Once the calibration measurements are obtained, the calibration values ​​may be stored in the lighting device (in step 22) so that the stored values ​​may be used later to compensate for changes in the luminous flux and / or chromaticity of the lighting device that may occur with changes in drive current, temperature, and time. In one embodiment, the calibration values ​​may be stored in a computer such as, for example, Figure 7 The calibration values ​​are shown in the table below. Fig.19 As discussed, the calibration value table may be stored in a storage medium of the lighting device.

[0181] Figure 7 Demonstrated that according to Figure 6 . In the illustrated embodiment, the calibration table includes six luminous flux measurements (Luma), six x chromaticity measurements (x chrom), and six y chromaticity measurements (y chrom) obtained from each emitting LED (e.g., white, blue, green, and red emitting LEDs) at three different drive currents (e.g., 10%, 30%, and 100% of the maximum drive current) and two different temperatures (T0, T1) in steps 10, 12, 14, 18, 20, and 22 of the calibration method. Figure 7 The calibration table shown in also includes six photocurrent measurements (Iph_d1) induced on the photodetector by the illumination produced by each of the emitting LEDs at three different drive current levels and two different temperatures in steps 10, 12, 16, 20 and 22 of the calibration method.

[0182] For each emitting LED (e.g., each white, blue, green, and red emitting LED) and each ambient temperature (T0, T1), Figure 7 The calibration table shown in also includes the forward voltage (Vfe) measured across the emission LED and the forward voltage (Vfd1) measured across the dedicated photodetector immediately after each of three different drive current levels are supplied to the emission LED. Figure 7 As shown in , in this exemplary embodiment, steps 10, 12, 16, 18, 20 and 22 of the calibration method result in six Vfe measurement results and six Vfd1 measurement results being stored for each emitting LED.

[0183] Figure 7 The calibration table shown in is only one example of calibration values ​​that can be stored in an LED lighting device according to the calibration method described herein. Figure 6 The calibration method shown in can be used to store substantially different calibration values ​​or substantially different numbers of calibration values ​​in a calibration table of an LED lighting device.

[0184] As indicated above, the present invention is not limited to Figure 6 and Figure 7 The exemplary number of drive current levels and drive current values ​​shown in FIG. It is certainly possible to obtain a greater / lesser number of optical and electrical measurements from the emitting LED and the at least one dedicated photodetector by applying a greater / lesser number of drive current levels to the emitting LED. Figure 7 In addition to the 10%, 30% and 100% of the maximum drive current shown in FIG. 1 , it is also possible to use drive currents of substantially different values.

[0185] It is also possible to obtain and store a different number of forward voltage (Vfe) measurements from the emitting LEDs, or forward voltage (Vfd1) measurements from the at least one dedicated photodetector. Figure 7 The calibration table shown in the embodiment stores six forward voltage (Vfe) measurements from each emitting LED and 6*n forward voltage (Vfd1) measurements from each dedicated photodetector, where 'n' is the number of emitting LEDs included in the lighting device. As noted above, the six Vfe measurements and 6*n Vfd measurements are preferably obtained at two different ambient temperatures (T0, T1) immediately after each operating drive current level (e.g., 10%, 30% and 100% of the maximum drive current) is applied to each emitting LED. Because this embodiment provides a good indication of how the emitter and detector junction temperatures change with changes in ambient temperature and changes in drive current, this embodiment is generally preferred. In addition, when only the detector forward voltage (Vfd1) is measured during operation of the device, this embodiment makes Fig.13 The compensation method shown in (and described below) is able to compensate for transmitter aging.

[0186] As in Figure 6 and Figure 7 As shown in and described above, the calibration method can obtain only one Vfe measurement result and only one Vfd1 measurement result for each emitting LED at a given temperature (e.g., T0) and a given drive current (e.g., 10% of the maximum drive current). In an alternative embodiment, Figure 6 The calibration method can obtain multiple Vfe measurement results and multiple Vfd1 measurement results for each emitting LED at a given temperature (e.g., T0) and a given drive current (e.g., 10% of the maximum drive current). The multiple Vfe and Vfd1 measurement results can be obtained in a short time period (e.g., 100 milliseconds), and the multiple Vfe measurement results and the multiple Vfd1 measurement results obtained in each time period are stored in Figure 7They can be averaged and filtered before being included in the calibration table.

[0187] In another alternative embodiment, as described in commonly assigned U.S. patent application serial numbers 13 / 970,944, 13 / 970,964, and 13 / 970,990, Figure 6 The calibration method can obtain only two forward voltage (Vfe) measurements from each emitting LED, one for each of the two different temperatures (T0, T1). Similarly, only 2*n forward voltage (Vfd1) measurements can be obtained from the dedicated photodetector, where 'n' is the number of emitting LEDs included in the lighting device. However, in this embodiment, the forward voltage (Vfe and Vfd1) measurements stored in the calibration table will only provide an indication of how the emitter and detector junction temperatures change with changes in ambient temperature and not with temperature changes induced by the drive current.

[0188] In another alternative embodiment of the present invention, Figure 6 The calibration method shown in can completely ignore the emitter forward voltage (Vfe) measurement and rely only on the photodetector forward voltage (Vfd1) measurement to provide a temperature indication. However, if the temperature difference between the emitting LED and the dedicated photodetector (s) remains relatively consistent over the operating temperature range, then only the Vfe measurement can be ignored. In order to maintain a consistent temperature difference between the emitting LED and the photodetector (s), a calibration method is provided herein and referred to below. Fig.18A Rather an improved transmitter module is described.

[0189] In yet another alternative embodiment of the present invention, Figure 6 The calibration method shown in can be used to obtain additional measurements that can later be used to compensate for phosphor aging and thereby control the chromaticity of a phosphor-converted white LED over time.

[0190] As noted above, some embodiments of the present invention may include phosphor-converted white emitting LEDs within an emitter module. These LEDs may be formed by coating or covering, for example, a blue LED having a peak emission wavelength of about 400 to 500 K with a phosphor material (e.g., YAG) for producing substantially white light having a CCT of about 3000 K. Other combinations of LEDs and phosphors may be used to form phosphor-converted LEDs capable of producing white or near-white light having a CCT in the range of about 2700 K to 10,000 K.

[0191] In phosphor-converted LEDs, the spectral content of the LED is combined with the spectral content of the phosphor to produce white or near-white light. Fig.21, the combined spectrum may include a first portion having a first peak emission wavelength (e.g., about 400 to 500) and a second portion having a second peak emission wavelength substantially different from the first peak emission wavelength (e.g., about 500 to 650). In this example, the first portion of the spectrum is generated by light emitted by a blue LED, and the second portion is generated by light passing through a phosphor (e.g., YAG).

[0192] As phosphor-converted LEDs age, the efficiency of the phosphor decreases, which makes the chromaticity of phosphor-converted LEDs appear "colder" over time. To explain the chromaticity shift associated with aging in phosphor-converted LEDs, Figure 6 In some embodiments of the calibration method shown in , it may be desirable to separately measure the photocurrent induced by the LED portion and the photocurrent induced by the phosphor portion of the phosphor-converted LED. Thus, some embodiments of the present invention may use two photodetectors of different colors to measure the photocurrents induced by different portions of the phosphor-converted LED spectrum, respectively. Specifically, an emitter module of a lighting device may include a first photodetector having a detection range configured to detect only a first portion of the spectrum emitted by the phosphor-converted LED; and a second photodetector having a detection range configured to detect only a second portion of the spectrum emitted by the phosphor-converted LED.

[0193] Typically, the detection ranges of the first and second photodetectors can be selected based on the spectrum of the phosphor-converted LED being measured. In an exemplary embodiment described above where the phosphor-converted white-emitting LED is included in an emitter module and implemented in the manner described above, the detection range of the first photodetector can be between about 400 nm and about 500 nm to measure the photocurrent induced by light emitted by the blue LED portion, and the detection range of the second photodetector can be between about 500 nm and about 650 nm to measure the photocurrent induced by light passing through the phosphor portion of the phosphor-converted white LED. The first and second photodetectors can include dedicated photodetectors and / or emitting LEDs that are sometimes configured to detect incident light.

[0194] As noted above, the emitter module of the lighting device preferably includes at least one dedicated photodetector. In one embodiment, the emitter module may include two dedicated photodetectors of different colors, such as one or more dedicated green photodetectors and one or more dedicated red photodetectors (see, e.g. Fig. 17B In another embodiment, the emitter module may include only one dedicated photodetector, such as a single red, orange, or yellow photodetector (see, e.g. Fig. 16B). In such embodiments, one of the emitting LEDs (eg, the green emitting LED) can sometimes be configured as a photodetector for measuring a portion of the phosphor-converted LED spectrum.

[0195] In the above described and Figure 6 In the calibration method shown in , the at least one dedicated photodetector can be used in step 16 to measure the photocurrent (Iph_d1) induced in the dedicated photodetector by the illumination generated by each of the emitting LEDs when the emitting LEDs are continuously driven to generate illumination at a plurality of different drive current levels (e.g., 100%, 30%, and 10% of the maximum drive level) and a plurality of different temperatures (e.g., T0 and T1). At some time before or after each of the photocurrent measurements (Iph_d1) is obtained from the dedicated photodetector, a forward voltage (Vfd1) is measured across the dedicated photodetector to provide an indication of the detector junction temperature at each of the calibrated drive current levels.

[0196] exist Figure 6 In some embodiments of the calibration method shown in , the dedicated photodetector used to obtain the photocurrent (Iph_d1) and forward voltage (Vfd1) measurements can be, for example, a red LED. When calibrating a phosphor-converted white LED, a dedicated red photodetector can be used to measure the light passing through the phosphor (i.e., Fig.21 In some embodiments, another dedicated photodetector (or one of the emitting LEDs) can be used to measure the LED portion of the phosphor-converted white LED (i.e., Fig.21 The photodetector can be, for example, a dedicated green photodetector or one of the green emitting LEDs.

[0197] As in Figure 7 As shown in , additional photodetectors can be Figure 6 Step 16 of the calibration method shown in FIG. 1 is used to measure the photocurrent (Iph_d2) induced in the additional photodetector by the illumination generated by the LED portion of the phosphor-converted white LED when the LED is continuously driven to generate illumination at a plurality of different drive current levels (e.g., 100%, 30%, and 10% of the maximum drive level) and a plurality of different temperatures (e.g., T0 and T1). In addition to measuring the photocurrent induced by the LED portion of the phosphor-converted white LED, the photocurrent (Iph_d2) induced by the illumination generated by the green-emitting LED can also be obtained from the additional photodetector in step 16 and measured. Fig.13The forward voltage (Vfd2) is measured across the additional photodetector before or after each of the photocurrent measurements (Iph_d2) is obtained from the additional photodetector to provide an indication of the detector junction temperature at each of the calibrated drive current levels.

[0198] In addition to storing individual photocurrent measurements (Iph_d2 and Iph_d1) of the phosphor-converted white LED, the calibration table may also store individual luminous flux (Luma), x chromaticity (x chrom), and y chromaticity (y chrom) measurements of the LED portion and the phosphor portion of the phosphor-converted white LED spectrum at each of the calibrated drive currents and temperatures. Figure 7 This is not explicitly shown in the present invention, but the luminous flux (Luma), x chromaticity (x chrom) and y chromaticity (y chrom) attributable to each portion of the phosphor-converted white LED spectrum are measured and these values ​​are stored in a calibration table. The stored calibration values ​​can be used later during one or more of the compensation methods described in this article to control the luminous flux and chromaticity of the LED portion and the phosphor portion of the phosphor-converted white LED, respectively, as if the LED were two different LEDs.

[0199] Now refer to Figure 6 and Figure 7 An exemplary method for calibrating a lighting device including a plurality of emitting LEDs and one or more photodetectors is described. Figure 6 The method steps shown in are described as occurring in a particular order, but one or more of the steps of the method shown may be performed in a substantially different order. In an alternative embodiment, for example, multiple electrical measurements (e.g., Iph, Vfd, and Vfe) may be obtained from one or more photodetectors and the emitting LED in step 16 before multiple optical measurements (e.g., Luma, xchrom, ychrom) are obtained from the emitting LED in step 14. In another alternative embodiment, an external calibration tool may obtain optical measurements (in step 14) at substantially the same time as the LED driver and receiver circuits obtain electrical measurements (in step 16). Although Figure 6 The calibration method shown in the embodiment stores the calibration values ​​in the lighting device at the end of the calibration method (e.g., in step 22), but a skilled artisan will recognize that these values ​​may be stored at substantially any time during the calibration process without departing from the scope of the present invention. The calibration method described herein is considered to include all such variations and alternative embodiments.

[0200] The calibration method provided herein improves upon conventional calibration methods in a number of ways. First, the method described herein calibrates each emitting LED (or LED chain) individually while turning off all other emitting LEDs that are not currently being tested. This not only improves the accuracy of the stored calibration values, but also enables the stored calibration values ​​to account for process variations between individual LEDs, as well as differences in output characteristics that inherently occur between LEDs of different colors.

[0201] Accuracy is further improved herein by supplying a relatively small (i.e., non-operating) drive current to the emitting LED and (multiple) photodetectors that is opposite to the operating drive current level typically used in conventional calibration methods when obtaining the forward voltage measurement. By using the non-operating drive current to obtain the forward voltage measurement, the present invention avoids inaccurate compensation by ensuring that the forward voltage for a given temperature and fixed drive current does not change significantly over time (due to the presence of parasitic resistance in the junction when the forward voltage measurement is obtained using the operating drive current).

[0202] As another advantage, the calibration method described herein obtains multiple optical measurements from each LED and multiple electrical measurements from each photodetector at multiple different drive current levels and multiple different temperatures. This further improves calibration accuracy by enabling accurate characterization of the nonlinear relationship between the luminous flux and the drive current, and the nonlinear relationship between the photocurrent and the drive current, for each individual LED. In addition, obtaining calibration values ​​at many different ambient temperatures improves compensation accuracy by enabling the compensation method (described below) to interpolate between stored calibration values, thereby enabling accurate compensation values ​​to be determined for the current operating temperature.

[0203] As yet another advantage, the calibration method described herein can use photodetectors of different colors to measure the photocurrent induced by different parts of the phosphor-converted LED spectrum (e.g., the LED part and the phosphor part). The photodetectors of different colors can also be used to measure the photocurrent induced by the reference emission LED whose peak emission wavelength falls within the LED part of the spectrum emitted by the phosphor-converted LED. By storing these calibration values ​​in the lighting device. The calibration values ​​can be used later to detect and account for chromaticity shifts that may occur in the phosphor-converted LED over time.

[0204] As described in more detail below, the calibration values ​​stored in the calibration table can be used in one or more compensation methods described herein to adjust the individual drive currents supplied to the emitting LEDs so as to obtain the desired luminous flux and desired chromaticity over time as the drive current changes, the temperature changes, and as the LED ages. For example, the luminous flux (Luma) measurement results can be used in some embodiments to maintain consistent lumen output and chromaticity as the temperature changes. In some embodiments, when the dimming level or color point setting of the lighting device is changed, the luminous flux (Luma) measurement results can be used together with the chromaticity (e.g., xchrom, ychrom) measurement results to obtain a new lumen output or a new target chromaticity. Regardless of the specific luminous flux or chromaticity setting used, the photocurrent (Iph) measurement results can be used to adjust the individual drive currents supplied to the emitting LEDs so as to account for the LED aging effects. When compensating LED lighting devices, although all such measurements can be used to obtain the most accurate results, those skilled in the art will understand how one or more of the calibration values ​​described herein can be used to improve the compensation methods performed by prior art lighting devices.

[0205] Exemplary embodiment of an improved method for controlling a lighting device

[0206] Figures 8 to 15 Exemplary embodiments of improved methods for controlling a lighting device that typically includes a plurality of emitting LEDs and at least one dedicated photodetector are presented. More specifically, Figures 8 to 15 Exemplary embodiments of improved compensation methods that can be used to adjust drive current supplied to individual LEDs of an LED lighting device to obtain desired luminous flux and desired chromaticity over time with variations in drive current, variations in temperature, and as the LEDs age are presented.

[0207] In some embodiments, Figures 8 to 15 The compensation method shown in can be used to control a lighting device having LEDs (all of which have the same color). However, because the output characteristics of LEDs of different colors vary in different ways with drive current, temperature, and time, the compensation method described herein is particularly suitable for controlling a lighting device that includes two or more LEDs of different colors (i.e., a multi-color LED lighting device). Because changes in drive current inherently affect the lumen output, color, and temperature of a lighting device, the compensation method described herein is also particularly suitable for controlling a lighting device that provides dimming and / or color adjustment capabilities (i.e., an adjustable LED lighting device).

[0208] 16 to 16 Fig. 20While describing exemplary embodiments of lighting devices, the figures show different types of LED lighting devices, each of which has one or more emitter modules. Fig. 16B , 17B , 18A and 18B, each emitter module may generally include a plurality of emitting LEDs arranged in an array, and one or more photodetectors spaced apart about the periphery of the array. In an exemplary embodiment, the emitting LED array may include red, green, blue and white (or yellow) LEDs, and the one or more photodetectors may include one or more red, orange, yellow and / or green LEDs. However, the present invention is not limited to any particular color, number, combination or arrangement of emitting LEDs and photodetectors. A skilled artisan will understand how the method steps described herein may be applied to other LED lighting devices having substantially different emitter modules.

[0209] According to one embodiment, Figure 8 An exemplary compensation method is presented that can be used to adjust the drive current supplied to individual LEDs of an LED lighting device in order to maintain a desired luminous flux and a desired chromaticity as temperature changes. Figure 8 The steps of the compensation method shown in solid outline in FIG. 1 are similar to those of commonly assigned U.S. patent application serial numbers 13 / 970,944, 13 / 970,964, and 13 / 970,990. Figure 5 The steps of the compensation method described in are similar to those of the present invention, which provides an improved lighting device and temperature compensation method.

[0210] However, previously filed applications fail to disclose methods for controlling a lighting device so as to maintain a desired luminous flux and a desired chromaticity over time, or so as to obtain a new luminous flux or a new chromaticity when changing a dimming level or color point setting of the lighting device. Figure 8 The optional method steps shown in dashed outline in FIG. 1 improve upon the compensation method described in the previously filed application by enabling precise control of luminous flux and chromaticity over a range of dimming levels and a range of color point settings. Fig.13 The compensation method shown in and discussed below further improves upon the compensation method described in the previously filed application by providing a method for maintaining a desired luminous flux and a desired chromaticity over time as the LED ages. Figure 8 and Fig.13 The compensation methods shown in can be used individually or together to provide accurate compensation for all LEDs used in a lighting device over variations in drive current, temperature, and time.

[0211] As in Figure 8As shown in , the improved compensation method may generally begin by substantially continuously driving a plurality of emitting LEDs to produce illumination (in step 30). When the lighting device is first turned “on”, the ambient temperature around the LEDs increases steadily over time until the temperature stabilizes. In some embodiments, the compensation method may be performed shortly after the lighting device is turned “on” and may be repeated a number of times until the temperature around the LEDs stabilizes. However, because changes in drive current and other factors affect the ambient temperature around the LEDs, the compensation method may be performed at other times during operation of the lighting device. Figure 8 The compensation method shown in .

[0212] In a preferred embodiment, the compensation method (in step 32) may be performed only when a significant change in the ambient temperature is detected. Fig. 20 As discussed, in some embodiments, the ambient temperature may be monitored by a dedicated temperature sensor or an additional LED that is used as both a temperature sensor and an optical sensor. A "significant change" may be any incremental increase or decrease in ambient temperature (e.g., 1°C) and is typically set to a specified amount within the control circuitry of the lighting device. If no significant temperature change is detected (the "no" branch in step 32), then the compensation method may continue to substantially continuously drive the plurality of emitting LEDs to produce illumination (in step 30). Otherwise, the compensation method may continue to step 36.

[0213] In some embodiments, the compensation method may also be performed if the dimming level and / or color point setting is changed in the adjustable lighting device. To accommodate such changes, the compensation method may monitor the target brightness (Ym) and target chromaticity settings (xm, ym) stored in the control circuit of the lighting device. In some embodiments, the target brightness (Ym) may be represented as a finite set of dimming levels, and the target chromaticity settings (xm, ym) may be represented as a series of x, y coordinates within the color gamut of the lighting device. In some embodiments, the target brightness (Ym) and target chromaticity settings (xm, ym) may be stored in hardware or software registers of the control circuit, for example, as 16-bit integer values, and may be changed by a user or building controller by storing alternative values ​​in the lighting device. If the control circuit does not detect any changes in the stored Ym, xm, and ym values ​​(the "no" branch in step 34), the compensation method may continue to substantially continuously drive the plurality of emitting LEDs to produce illumination (in step 30). Otherwise, the compensation method may continue to step 36.

[0214] As used herein, the term "substantially continuously" refers to supplying the plurality of emitting LEDs with an operating drive current almost continuously, except for periodic intervals during which the plurality of emitting LEDs are temporarily "turned off" for a shorter duration (in step 36). Figure 8 In an exemplary embodiment of , a periodic interval is used to obtain a forward voltage (Vfe) from each of the emitting LEDs, one LED at a time (in step 38). Fig.13 and Fig.14 These periodic intervals may also be used for other purposes, as shown in and discussed in more detail below.

[0215] Fig. 9 is an exemplary timing diagram illustrating a timing diagram of a Figure 8 The steps 30, 36 and 38 of the compensation method shown in FIG. Figure 8 and Fig. 9 As shown in Fig. 9 Generally indicated as I1 in FIG. 1 ) to substantially continuously drive a plurality of emitting LEDs to produce illumination (in Figure 8 by removing the drive current or at least reducing the drive current to a non-operating level (in step 30 of Fig. 9 The plurality of emitting LEDs are generally indicated as I0 in the figure to turn off the plurality of emitting LEDs for a short duration (in the periodic interval) Figure 8 In step 36 of ). Between the periodic intervals, the lighting device produces continuous illumination as DC current is supplied to the LED.

[0216] During each periodic interval, a relatively small non-operating drive current (e.g., about 0.1 to 10 mA, Fig. 9 ) to drive an emitting LED and measure the forward voltage (e.g., Vfel) generated across the LED. Fig. 9 In this manner, the forward voltage (e.g., Vfe1, Vfe2, Vfe3, and Vfe4) is measured across each emitting LED, one LED at a time, as shown in FIG. In some cases, the forward voltage associated with each individual emitting LED may be averaged over a period of time, filtered to eliminate erroneous data, and stored, for example, in a register of the lighting device.

[0217] Fig. 9 An exemplary timing diagram is provided for measuring a present forward voltage (i.e., Vfe_current, or the forward voltage developed across an emitting LED during operation of the device) which provides an indication of the present junction temperature of each emitting LED included in the lighting device. Fig. 9An exemplary timing diagram is provided for a lighting device including four emitting LEDs (e.g., RGBY or RGBW), but the timing diagrams and methods described herein can be easily modified to accommodate a smaller or larger number of emitting LEDs. As described in more detail below, the timing diagrams described herein can also be easily modified to accommodate, for example, a plurality of emitting LEDs. Fig.14 Additional measurement results are shown in .

[0218] In an alternative embodiment, Figure 8 The compensation method may measure the detector forward voltage (Vfd_current) generated across one or more photodetectors in step 38 instead of Figure 8 and Fig. 9 . However, if the temperature difference between the emitting LED and the photodetector(s) remains relatively consistent over the operating temperature range, then the detector forward voltage can only be used in the compensation method described herein. In order to maintain a substantially consistent temperature difference between the emitting LED and the photodetector(s), a compensation method is provided herein and referred to below. Fig.18A Rather an improved transmitter module is described.

[0219] In some embodiments of the present invention, if a temperature change is detected in step 32, but the target brightness (Ym) and target chromaticity settings (xm, ym) are not changed in step 34, then Figure 8 The compensation method shown in can continue to step 46. Figure 8 and Fig.10 As shown in , the compensator can use the following items to determine the drive current (Ix) required to achieve the desired luminous flux (Lx) of each emitting LED: the current forward voltage (Vfe_current), Figure 6 A table of stored calibration values ​​generated during a calibration method of Figure 8 In step 46 of ). For example, the compensation method can interpolate between the stored luminous flux calibration values ​​to calculate the luminous flux value that would be expected for the current forward voltage at each of the previously calibrated (i.e., known) drive current levels. Once the luminous flux values ​​are calculated at each of the calibrated drive current levels, if the expected luminous flux is different from one of the calculated luminous flux values, another interpolation technique can be used to determine the unknown drive current (Ix) required to produce the expected luminous flux (Lx).

[0220] Fig.10 is a graphical representation depicting how one or more interpolation techniques may be used to determine the drive current (Ix) required to produce the desired luminous flux (Lx) in the stored calibration value. Fig.10 , the six solid dots (·) represent the luminous flux calibration values ​​obtained during calibration at three different drive currents (e.g., 10%, 30% and 100% of the maximum drive current) and two different temperatures (e.g., T0 and T1). As noted above, the luminous flux calibration values ​​(·) are previously stored in the calibration value table for each emitting LED included in the lighting device (see, e.g., Figure 7 )Inside.

[0221] To determine the drive current (Ix) required to produce the desired luminous flux (Lx) of a given LED, Figure 8 The compensation method interpolates between each of the stored calibration values ​​(·) to calculate the luminous flux value (△) that should be produced at the current operating temperature (Vfe_current) when using the same three drive currents (e.g., 10%, 30% and 100% of the maximum drive current). If the expected luminous flux (Lx) is different from one of the calculated luminous flux values ​​(△), then Figure 8 The compensation method can apply another interpolation technique to the calculated luminous flux value (△) to generate a relationship between them (in Fig.10 Based on this relationship, the driving current (Ix) required to generate the desired luminous flux (Lx) can be determined.

[0222] In some embodiments, the interpolation technique(s) used to calculate the luminous flux value (Δ) and the relationship between the values ​​used to generate the calculations may depend on the color of the LED being compensated. For example, the luminous flux versus junction temperature (or forward voltage) relationship for blue, green, and white LEDs is substantially linear over the operating temperature range (see Figure 2 ). The compensation method is able to calculate the luminous flux values ​​(Δ) for the blue, green, and white LEDs at the current forward voltage by linearly interpolating between the stored calibration values ​​at each of the calibrated drive current levels because of this linear relationship. However, the red, orange-red, and yellow LEDs exhibit a substantially more nonlinear relationship between luminous flux and junction temperature (see Figure 3 ). For these LEDs, a higher order interpolation technique can be used to calculate the luminous flux value (Δ) for each of the calibrated drive current levels at the current forward voltage.

[0223] In one embodiment, the higher order interpolation technique may take the form of quadratic interpolation, which follows the general equation:

[0224] ax 2 +bx+c=y (EQ.1)

[0225] Wherein, 'x' is Vf (or temperature); 'y' is luminous flux; and 'a', 'b', and 'c' are coefficients. If forward voltage and luminous flux values ​​were previously obtained at three different temperatures during the calibration phase, the 'a', 'b', and 'c' coefficients can be accurately determined by inserting the stored calibration values ​​into EQ.1 and solving the equations for 'a', 'b', and 'c', respectively. On the other hand, as described above, if the LED is calibrated at only two different temperatures, the 'a' coefficient can be obtained from the data sheet provided by the LED manufacturer, while the 'b' and 'c' coefficients are determined from the calibration values. Although the latter method (sometimes referred to as "Poor Man's Quadratic Interpolation") may sacrifice a small amount of accuracy, it may represent an acceptable trade-off between accuracy and calibration cost. In some embodiments, the calibration value table may store actual (e.g., measured) luminous flux calibration values ​​or only the coefficients needed to perform higher-order interpolation. In other embodiments, a combination of measured values ​​and coefficients may be stored in the calibration table.

[0226] In some embodiments, if the desired luminous flux (Lx) is different from one of the calculated values, then the relationship between the calculated luminous flux values ​​(Δ) may be determined by another interpolation technique ( Fig.10 However, since the relationship between luminous flux and driving current is nonlinear for all LED colors (see Figure 4 and Figure 5 ), so the relationship is preferably obtained by performing a higher order interpolation on the calculated luminous flux values. Alternatively, a piecewise linear interpolation can be used to characterize the nonlinear relationship between the calculated luminous flux values, or a typical curvature can be assumed from a data sheet provided by the LED manufacturer.

[0227] In some embodiments, an appropriate interpolation technique may be selected based on a tradeoff between memory and processing requirements and / or based on the particular color of the LED being compensated. As noted above, some LED colors, such as blue and green, exhibit a more nonlinear luminous flux versus drive current relationship than other LED colors, such as red and orange-red (see Figure 4 and Figure 5 ). LED colors that exhibit substantially more nonlinear behavior (e.g., blue and green) can be more accurately compensated for by obtaining more luminous flux calibration values ​​and using piecewise linear interpolation techniques, or by obtaining fewer calibration values ​​and using higher order interpolation techniques or assumed curvature to generate a nonlinear relationship between luminous flux and drive current.

[0228] Once the relationship between the luminous flux and the driving current of a given LED is obtained, it can be obtained from Fig.10The driving current (Ix) required to produce the desired luminous flux (Lx) is selected from the generated relationship shown in the example of . Then, the selected driving current can be used to drive the LED to produce lighting with the desired luminous flux (in Figure 8 In step 48 of ). This process is performed for each emitting LED until each LED is configured to produce the desired luminous flux (Lx) at the current operating temperature (Vfe_current). The drive current supplied to the LED can be adjusted in the following ways to meet the selected drive current: either adjusting the drive current level (i.e., current dimming) or changing the duty cycle of the drive current through pulse width modulation (PWM) dimming.

[0229] In some embodiments, if the target brightness (Ym) and / or target chromaticity settings (xm, ym) are changed in step 34, then Figure 8 The compensation method shown in may perform additional steps (e.g., steps 40, 42, and 44). As noted above, the target brightness (Ym) or target chromaticity setting (xm, ym) may be changed by a user or building controller in order to adjust the dimming level or color point setting of the adjustable LED lighting device. If a change in the target brightness or chromaticity is detected in step 34, the compensation method may determine the drive current (Idrv) currently supplied to each of the emitting LEDs (in step 40). The current drive current (Idrv) may be obtained from the LED driver circuit. Although in Figure 8 3 as occurring after measuring the present forward voltage (Vfe_current) in step 38, but in alternative embodiments of the present invention, the present drive current (Idrv) may be determined prior to measuring the forward voltage.

[0230] Once the current forward voltage and current drive current are determined, the compensation method can determine the expected chromaticity value (xi, yi) for each emitting LED (in step 42) using the following: the current forward voltage measured across the LED (Vfe_current), the current drive current supplied to the LED (Idrv), Figure 6 A table of stored calibration values ​​generated during a calibration method of the present invention, and one or more interpolation techniques. Fig.11 and Fig.12 Depicted is how one or more interpolation techniques may be used to determine the expected x and y chromaticity values ​​(xi , yi ) for a given LED at a current operating temperature (Vfe_current) and a current drive current (Idrv) from a table of stored calibration values.

[0231] exist Fig.11 and Fig.12In FIG. 1 , the solid dots (·) represent the x and y chromaticity calibration values ​​obtained during calibration at three different drive currents (e.g., 10%, 30%, and 100% of the maximum drive current) and two different temperatures (e.g., T0 and T1). As noted above, the x and y chromaticity calibration values ​​(·) are stored in the calibration value table for each emitting LED included in the lighting device (see, e.g., Figure 7 ). To determine the expected x and y chromaticity values ​​(xi , yi ) for a given LED, Figure 8 The compensation method interpolates between the stored calibration values ​​(·) to calculate the x and y chromaticity values ​​(△) that should be produced at the current operating temperature (Vfe_current) when the same three drive currents (e.g., 10%, 30%, and 100% of the maximum drive current) are used. In most cases, linear interpolation techniques can be used to calculate the x and y chromaticity values ​​(△) at the current operating temperature (Vfe_current). However, if the x and y chromaticity values ​​are calibrated at more than two temperatures, nonlinear interpolation techniques can be used to calculate the x and y chromaticity values ​​(△) at the current operating temperature (Vfe_current).

[0232] If the drive current (Idrv) currently supplied to the emission LED is different from one of the calibrated drive current values, then Figure 8 The compensation method can apply another interpolation technique to the calculated x and y chromaticity values ​​(△) to generate a relationship between them (in Fig.11 and Fig.12 Based on this relationship, the current drive current (Idrv) can be determined to determine the expected x and y chromaticity values ​​(xi, yi).

[0233] The interpolation technique used to generate the relationship between the calculated x and y chromaticity values ​​(△) can generally depend on the color of the compensated LED. As pointed out above, the chromaticity changes with drive current and temperature are significantly different for LEDs of different colors. For red LEDs, the peak emission wavelength increases relatively linearly with the drive current, but increases significantly with temperature. The peak emission wavelength of the green LED decreases nonlinearly with the drive current to some extent and increases slightly with temperature. Although the peak emission wavelength of the green LED changes very little with temperature, it decreases very nonlinearly with the drive current. In some embodiments, a piecewise linear interpolation technique can be used to generate the relationship between the calculated x and y chromaticity values ​​(△), or a typical curvature can be assumed from the data table provided by the LED manufacturer. However, in other embodiments, when compensating for certain colors of LEDs (e.g., green LEDs) that exhibit more significant nonlinear chromaticity changes with the drive current, a higher order interpolation technique can be used to increase accuracy.

[0234] The expected x and y chromaticity for each emitting LED can be expressed as a color point in the form of (xi, yi). In a lighting device including four emitting LEDs, step 42 of the compensation method can result in the generation of four expected color points: (x1, y1), (x2, y2), (x3, y3), and (x4, y4). Once the expected color points are determined in step 42, the compensation method can calculate the relative lumens required from each of the emitting LEDs to achieve the target brightness (Ym) and target chromaticity settings (xm, ym) in step 44. For example, when the light from the four emitting LEDs is combined, the target brightness (Ym) of the combined light can be expressed as:

[0235] Ym=Y1+Y2+Y3+Y4 (EQ.2)

[0236] Wherein, Y1, Y2, Y3 and Y4 represent the relative lumens of the four emitting LEDs. The relative lumen values ​​(Y1, Y2, Y3 and Y4) can be calculated using the well-known color mixing equations; the target brightness (Ym) and target chromaticity (xm, ym) can be set in the lighting device; and the expected color points (x1, y1), (x2, y2), (x3, y3) and (x4, y4) can be determined in step 42 of the compensation method. Since these equations are well-known and easily understood by skilled artisans, further description of such equations is omitted herein.

[0237] Once the relative lumens (Y1, Y2, Y3 and Y4) of each emitting LED is calculated (in step 44), the drive current that should be supplied to each emitting LED to achieve the target brightness (Ym) is determined in step 46 in a manner similar to that described above. However, instead of determining the drive current (Ix) required to achieve the "desired luminous flux" (Lx) from each emitting LED, the current embodiment determines the drive current (Ix) required to achieve the relative lumen values ​​(Y1, Y2, Y3 and Y4) calculated for each emitting LED in step 44. Once the individual drive currents (Ix) are determined in step 46, the determined drive currents are used in step 48 to drive the emitting LEDs to produce illumination having the desired luminous flux and the desired chromaticity.

[0238] Whenever a significant temperature change is detected (in step 32) and / or a target brightness or target chromaticity setting is changed (in step 34), Figure 8 The compensation method shown in can be used to adjust the drive current supplied to the emitting LED. However, because changes in the drive current inherently affect the LED junction temperature, it is usually possible to repeat Figure 8The method steps shown in are repeated many times until the temperature stabilizes and the target brightness and chromaticity values ​​remain constant.

[0239] Now refer to Figures 8 to 12 Instead, one embodiment of a compensation method for controlling an LED lighting device as drive current and temperature vary is described. Although the compensation method described herein refers to target chromaticity settings and chromaticity calibration values ​​from the CIE 1931 XYZ color space, a person skilled in the art will readily understand how the compensation method can be modified to use target chromaticity settings and chromaticity calibration values ​​from other color spaces such as the CIE 1931 RGB color space, the CIE 1976 LUV color space, and various other RGB color spaces (e.g., sRGB, Adobe RGB, etc.). For this reason, the compensation method described herein and in the claims is considered to include any color space that can be used to describe the color gamut of an LED lighting device that substantially includes any combination of emitting LEDs as described herein.

[0240] Compared with conventional compensation methods, Figure 8 The compensation method shown in provides many advantages. As noted above, conventional methods typically measure the forward voltage by applying an operating drive current level to the emitting LED. Unfortunately, the forward voltage measured at the operating drive current level varies significantly over the life of the LED. As the LED ages, the parasitic resistance within the junction increases, which in turn causes the forward voltage measured at the operating current level to increase over time (regardless of temperature). To this end, the present compensation method uses a relatively small drive current (e.g., about 0.1 mA to about 10 mA) to obtain forward voltage measurements from each emitting LED individually while turning off all emitting LEDs that are not currently being tested. This improves the accuracy of the operating forward voltage value and enables individual compensation for temperature and process for each emitting LED.

[0241] Conventional methods often rely on typical values ​​or a linear relationship between luminous flux and drive current when performing temperature compensation. In contrast, the compensation method described herein interpolates between multiple stored luminous flux calibration values ​​obtained at different drive currents and different temperatures, and obtains a nonlinear relationship between the luminous flux and drive current for each LED at the current operating temperature (Vfe_current). This enables the compensation method to accurately and individually characterize the luminous flux to drive current relationship of each LED included in the lighting device, and to provide accurate temperature compensation regardless of the process. Therefore, the compensation method described herein provides accurate control of luminous flux as temperature changes.

[0242] When the dimming level or color point setting is changed by the user or the building controller, Figure 8 The compensation method shown in improves upon conventional compensation methods by providing a more accurate method for controlling the brightness and chromaticity of a lighting device. When a lighting device detects a change in target brightness or target chromaticity, the drive current supplied to the emitting LED must be adjusted in order to achieve the new target value(s). The compensation method described herein increases the accuracy of determining the new drive current by interpolating between multiple stored chromaticity calibration values ​​obtained at different temperatures, and obtaining the relationship between the chromaticity and the drive current of each emitting LED at the current operating temperature (Vfe_current). This enables the present compensation method to accurately determine the expected chromaticity value that should be produced for each emitting LED at the current operating temperature and the current drive current. Therefore, the compensation method described herein provides accurate control of chromaticity as the drive current changes.

[0243] Although Figure 8 The compensation method shown in provides an accurate method for controlling the luminous flux and chromaticity of LED lighting devices as the driving current and temperature change, but it does not account for the LED aging effect. To mitigate this effect, Fig.13 Improved methods are provided for maintaining desired luminous flux and desired chromaticity as LEDs age over time. As noted above, Figure 8 and Fig.13 The compensation methods shown in can be used individually or together to provide accurate compensation for all LEDs used in a lighting device over variations in drive current, temperature, and time.

[0244] Typically, this can be performed repeatedly throughout the life of the lighting device. Fig.13 The compensation method shown in , in order to account for the LED aging effects. It can be performed at essentially any time (when the lighting device is first "switched on"), or at periodic or random intervals throughout the life of the device. Fig.13 In some embodiments, the method shown in can be performed after a change in temperature, dimming level, or color point setting is detected. Fig.13 The compensation method shown in Figure 8 The drive current value determined in the compensation method is fine-tuned.

[0245] As in Fig.13As shown in , the aging compensation method can generally be started by substantially continuously driving a plurality of emitting LEDs to produce illumination, for example, by applying an operating drive current (Idrv) to each of the plurality of emitting LEDs (in step 50). As noted above, the term "substantially continuously" means that the operating drive current is applied to the plurality of emitting LEDs almost continuously, except for periodic intervals during which the plurality of emitting LEDs are temporarily turned off for a shorter duration (in step 52). Fig.13 In the method shown in , periodic intervals can be used to obtain various measurements from a dedicated photodetector (e.g., a red photodetector) included in the lighting device or an emitting LED (e.g., a red emitting LED) configured to detect incident light. For example, in step 54, the periodic intervals are used to measure the photocurrent (Iph) induced on the photodetector in response to the illumination generated by each emitting LED and received by the photodetector, one LED at a time. In step 56, the periodic intervals are used to obtain the forward voltage (Vfd) generated across the photodetector after a relatively small (i.e., non-operating) drive current is applied to the photodetector.

[0246] Fig.14 is an exemplary timing diagram illustrating a timing diagram of a Fig.13 The steps 50, 52, 54 and 56 of the compensation method shown in FIG. Fig.13 and Fig.14 As shown in Fig.14 Generally indicated as I1 in FIG. 1 ) to substantially continuously drive a plurality of emitting LEDs to produce illumination (in Fig.13 By removing the drive current or at least reducing the drive current to a non-operating level (in step 50 of Fig.14 The plurality of emitting LEDs are generally indicated as I0 in the figure to turn off the plurality of emitting LEDs for a short duration (in the periodic interval) Fig.13 In step 52 of ). Between the periodic intervals, the lighting device produces continuous illumination as DC current is supplied to the emitting LED.

[0247] During some of the periodic intervals, one emitting LED is driven to produce illumination using an operating drive current level (I1), while the remaining LEDs remain "off", and the photocurrent (e.g., Iph1) induced in the photodetector by the illumination from the driven LED is measured. Fig.14 Neutralization Fig.13As shown in step 54 of , the photocurrent induced on the photodetector by the illumination produced by each of the emitting LEDs (e.g., Iph1, Iph2, Iph3, and Iph4) is measured, one LED at a time. Fig.14 Exemplary timing diagrams are provided for a lighting device including four emitting LEDs (eg, RGBY or RGBW), but the timing diagrams described herein may be readily modified to accommodate smaller or larger numbers of emitting LEDs.

[0248] At some time before or after obtaining the photocurrent (Iph) measurement, the forward voltage (Vfd) is measured across the photodetector by applying a relatively small non-operating drive current (e.g., about 0.1 to 0.3 mA) to the photodetector. Fig.13 This forward voltage measurement (also referred to herein as Vfd_current) provides an indication of the current junction temperature of the photodetector. Fig.14 The timing diagram of shows only one forward voltage (Vfd) measurement obtained from a single photodetector, but the timing diagram can be easily modified to accommodate a larger number of photodetectors.

[0249] In an exemplary embodiment, the presently described compensation method can be utilized within a lighting device that includes multiple photodetectors implemented using LEDs of different colors. Specifically, each emitter module of the lighting device can include one or more red LEDs and one or more green LEDs as photodetectors. In such an embodiment, forward voltage measurements (Vfd) can be obtained from the photodetectors by applying a small drive current to each photodetector (in step 56). In many cases, the photocurrent associated with each emitting LED (Iphl, Iph2, Iph3, Iph4) and the forward voltage (s) associated with each photodetector (Vfd) can be averaged over a period of time, filtered to eliminate erroneous data, and stored, for example, in a register of the lighting device.

[0250] In addition to the photocurrent and the detector forward voltage(s), Fig.14 The periodic intervals shown in can be used to obtain the above Figure 8 and Fig. 9The periodic intervals may also be used for other purposes not specifically shown herein. For example, some of the periodic intervals may be used by a photodetector to detect light originating from outside the lighting device, such as ambient light or light from other lighting devices. In some cases, the ambient light measurements may be used to turn the lighting device on when the ambient light level drops below a threshold (i.e., when it gets darker), and to turn the lighting device off when the ambient light level exceeds another threshold (i.e., when it gets brighter). In other cases, the ambient light measurements may be used to adjust the lumen output of the lighting device as the ambient light level changes, for example, to maintain a consistent brightness level in the room. If the periodic intervals are used to detect light from other lighting devices, then in Fig.13 When obtaining photocurrent and detector forward voltage measurements in a compensation scheme, the detected light can be used to avoid interference from other lighting devices.

[0251] In other embodiments, periodic intervals can be used to measure different portions of the spectrum of a particular LED using two or more different colored photodetectors. For example, the spectrum of a phosphor-converted white LED can be divided into two portions, and each portion can be measured separately using two different photodetectors at two different periodic intervals. Specifically, a first periodic interval can be used to detect a photocurrent induced on a first photodetector (e.g., a green photodetector) by a first spectral portion (e.g., about 400nm to about 500nm) of the phosphor-converted white LED. A second periodic interval can be used to detect a photocurrent induced on a second photodetector (e.g., a green photodetector) by a second spectral portion (e.g., about 500nm to about 650nm) of the phosphor-converted white LED. As described in more detail below, dividing the spectrum of a phosphor-converted white LED into two portions, and using two different colored photodetectors to separately measure each portion can enable Fig.13 The compensation method detects and accounts for the chromaticity changes that occur as phosphor-converted LEDs age.

[0252] Once the photocurrent and detector forward voltage(s) are measured, Fig.13 The compensation method shown in FIG. 5 can determine the expected photocurrent (Iph_expected) for each emitting LED (in step 58) using the following: the current forward voltage (Vfd_current) currently measured across the photodetector, the current drive current (Idrv) currently applied to the LED, Figure 6 A table of stored calibration values ​​generated during a calibration method of the present invention, and one or more interpolation techniques. Fig.15Depicted is how one or more interpolation techniques may be used to determine the expected photocurrent (Iph_expected) for a given LED at the current operating temperature (Vfd_current) and the current drive current (Idrv) from a table of stored calibration values.

[0253] exist Fig.15 In FIG. 1 , the solid dots (·) represent photocurrent calibration values ​​obtained during calibration at three different drive currents (e.g., 10%, 30%, and 100% of the maximum drive current) and two different temperatures (e.g., T0 and T1). As noted above, the photocurrent calibration values ​​(·) are stored in a calibration value table for each emitting LED included in the lighting device (see, e.g., FIG. 1 ). Figure 7 ). To determine the expected photocurrent (Iph_expected) for a given LED, Fig.13 The compensation method interpolates between stored calibration values ​​(·) to calculate the photocurrent value (△) that should be generated at the current operating temperature (Vfd_current) when using the same three drive currents (e.g., 10%, 30% and 100% of the maximum drive current).

[0254] Because the emission power and responsiveness of the photodetector decrease linearly with temperature, the change in photocurrent with temperature is nonlinear for all LED colors. To this end, a nonlinear interpolation technique can be used to calculate the photocurrent value (△) for all LED colors at the current operating temperature. In some embodiments, the nonlinear interpolation technique can be a higher order interpolation, a "Pullmans" quadratic interpolation, or an assumed curvature. In other embodiments, the results of two different linear interpolations (e.g., a linear interpolation between emission power and temperature, and a linear interpolation between detector responsiveness and temperature) can be multiplied together to calculate the photocurrent value (△) at the current operating temperature.

[0255] If the drive current (Idrv) currently supplied to the emission LED is different from one of the calibrated drive current values, then Fig.13 The compensation method can apply another interpolation technique to the calculated photocurrent values ​​(△) to generate a relationship between them (in Fig.15 In some cases, a higher order interpolation of the calculated photocurrent values ​​(Δ) can be used to generate a nonlinear relationship between the photocurrent and the drive current. In other cases, a piecewise linear interpolation can be used to characterize the nonlinear relationship between the calculated photocurrent values, or a typical curvature can be assumed from a data sheet provided by the LED manufacturer. Based on the generated relationship, an expected photocurrent value (Iph_expected) can be determined for the current drive current (Idrv).

[0256] Once the expected photocurrent (Iph_expected) for each emitting LED is determined (in step 58), Fig.13 The compensation method shown in FIG. 6 calculates a scaling factor for each emitting LED by dividing the expected photocurrent for each LED (Iph_expected) by the measured photocurrent for each LED (e.g., Ipdl) (in step 60). Next, the compensation method applies each scaling factor to the expected luminous flux value of each emitting LED to obtain an adjusted luminous flux value for each emitting LED (in step 62). In some embodiments, the expected luminous flux value may be, for example, Figure 8 One of the relative lumen values ​​(Y1, Y2, Y3 and Y4) calculated in step 44 of the compensation method shown in FIG. 1 is adjusted to account for any changes in the target brightness (Ym) and / or target chromaticity (xm, ym) settings stored within the lighting device. Finally, if there is a difference between the expected photocurrent and the measured photocurrent for any of the emitting LEDs, the drive current currently applied to the emitting LED is adjusted (in step 64) to achieve the adjusted luminous flux value.

[0257] The above described and Fig.13 The compensation method presented in provides an accurate method for adjusting the individual drive currents applied to the emitting LEDs, avoiding compensating for the reduction in lumen output that occurs over time as the LEDs age. By accurately controlling the luminous flux produced by each emitting LED, the compensation method accurately controls the color of an LED lighting device that includes multiple multi-color non-phosphor converted emitting LEDs. However, and as noted above, some embodiments of the present invention may include phosphor converted emitting LEDs (e.g., white or yellow LEDs) within the emitter module. In such embodiments, additional steps may be taken to control the luminous flux and chromaticity of the phosphor converted LEDs over time.

[0258] Like non-phosphor converted LEDs, the luminous flux produced by phosphor converted LEDs generally decreases over time. However, unlike non-phosphor converted LEDs, phosphor converted LEDs are also susceptible to changes in chromaticity over time because the efficiency of the phosphor decreases as the phosphor ages. When phosphor converted LEDs are included in an emitter module, Fig.13 The compensation method shown in can be used to detect and account for chromaticity shifts that occur in phosphor-converted LEDs by separately measuring and compensating for chromaticity shifts caused by phosphor aging. To do this, two separate photodetectors can be included within the emitter module for measuring photocurrents induced in two different portions of the phosphor-converted LED spectrum. In some embodiments, the emitter module can include two dedicated photodetectors of different colors (e.g., Fig. 17B ) for measuring the phosphor-converted LED spectrum (e.g., in Fig.21In other embodiments, only one dedicated photodetector (e.g., Fig. 16B ) can be included in the emitter module, and one of the emission LEDs (e.g., the green emission LED) can sometimes be used as an additional photodetector.

[0259] In order to detect and account for the chromaticity shift that occurs over time in a phosphor-converted white LED, different parts of the phosphor-converted LED spectrum must first be calibrated. For example, a dedicated red photodetector and a dedicated green photodetector (or green-emitting LED) can both be used in Figure 6 Step 16 of the calibration method of is used to obtain a photocurrent measurement from a phosphor-converted white LED. The white LED-on-red detector photocurrent measurement is stored as "Iph_d1" Figure 7 The photocurrent measurement result of the white LED-on-greendetector is stored as "Iph_d2" in Figure 7 The Iph_d2 calibration value is in Figure 7 ' are italicized to indicate that they are optional values ​​that can only be obtained when a phosphor-converted LED is included in an emitter module.

[0260] As described above and in Figure 7 As shown in , Iph_d1 and Iph_d2 calibration values ​​of the phosphor-converted white LED can be obtained at three different drive currents (e.g., 10%, 30%, and 100% of the maximum drive current) and at each of two different temperatures (e.g., T0 and T1). The white LED photocurrent (Iph_d2) measurement result on the green detector indicates the blue LED portion of the phosphor-converted white LED (i.e., Fig.21 The photocurrent induced in the green photodetector (or green emitting LED) by the light emitted from the first portion shown in FIG. 1 . The white LED photocurrent (Iph_d1) measurement on the red detector indicates the phosphor portion of the phosphor-converted white LED (i.e., Fig.21 The light of the second part (shown in FIG. 1 ) induces a photocurrent in the red photodetector.

[0261] At some time before or after each Iph_d1 and Iph_d2 measurement is obtained, the forward voltage (Vfd1 or Vfd2) is measured across the dedicated red photodetector and the dedicated green photodetector (or green emitting LED) to provide an indication of the red detector junction temperature and the green detector junction temperature at each of the calibrated drive current levels and ambient temperatures. The Vfd1 and Vfd2 measurements may be stored in a Figure 7 The calibration table is shown in .

[0262] exist Fig.13 During the compensation method of FIG. 5 , the red detector white LED photocurrent (Iph_d1) and the green detector white LED photocurrent (Iph_d2) can be measured in a manner as described in step 54, and the expected photocurrents (Iph_expected) of the red detector white LED and the green detector white LED can be determined in a manner as described in steps 56 to 58. Next, as described in step 60, the expected photocurrents (Iph_expected) determined in step 58 can be divided by the photocurrents measured in step 54 to produce the red detector white LED and the green detector white LED, respectively. The green detector white LED scale factor provides an indication of how the relative lumens of the LED portion of the phosphor-converted LED has changed over time. The red detector white LED scale factor provides an indication of how the relative lumens of the phosphor portion of the phosphor-converted LED has changed over time. In some embodiments, the green detector white LED scale factor and the red detector white LED scale factor can be used to control the luminous flux and chromaticity of the phosphor-converted white LED as if it were two separate LEDs.

[0263] For example, the white LED scaling factor on the red detector may be applied to the overall expected luminous flux value of the phosphor-converted LED in step 62 to account for lumen variations due to LED and phosphor aging. In some cases, the overall expected luminous flux value of the phosphor-converted LED may be calculated by applying Figure 8 The relative lumen values ​​calculated for the LED portion and the phosphor portion of the phosphor-converted LED in steps 40 to 44 of the compensation method are added together to determine. Figure 6 As described above, in order to calculate the relative lumen values ​​of the LED part and the phosphor part respectively, Figure 8 The compensation method may use previously stored luminous flux, x-chromaticity, and y-chromaticity calibration values ​​for each portion of the phosphor-converted LED spectrum.

[0264] To account for the chromaticity shift of the phosphor-converted white LED over time, the white LED scale factor on the green detector can be compared to the white LED scale factor on the red detector. Based on this comparison, the actual chromaticity of the phosphor-converted LED can be determined using the well-known color mixing equations, and the overall chromaticity of the lighting device can be maintained by adjusting the drive current applied to all emitting LEDs.

[0265] While the methods described above provide acceptable solutions for controlling the luminous flux and chromaticity of a phosphor-converted white LED over time, in some embodiments the chromaticity of a phosphor-converted white LED may be more accurately determined by accounting for detector aging. For example, the photocurrent induced on the red and green photodetectors (or green emitting LEDs) by a given amount of incident light typically decreases over time. Although this decrease is typically not large, it may cause the white LED scale factor on the green detector and the white LED scale factor on the red detector to also decrease over time, which in turn reduces the accuracy of adjusting the chromaticity of the phosphor-converted white LED. In some embodiments, in order to eliminate this source of measurement error, the scale factor generated for the phosphor-converted LED in step 60 may be adjusted to account for detector aging. This may be accomplished, for example, by using a blue emitting LED as a reference for the phosphor-converted white LED.

[0266] In some embodiments, both a dedicated red photodetector and a dedicated green photodetector (or a green emitting LED) may be provided. Fig.13 Step 54 of the compensation method is used to obtain the Iph_d1 and Iph_d2 photocurrent measurements from the blue emitting LED. After measuring the forward voltage across the red and green detectors in step 56, the Fig.13 In some embodiments, the blue LED-on-red detector scale factor may be applied to the desired luminous flux of the blue emission / reference LED in step 62 to adjust the luminous flux produced by the blue emission / reference LED. In some embodiments, the desired luminous flux value of the blue emission / reference LED may be calculated using the following formula: Figure 8 The relative lumen values ​​are calculated in the manner described in steps 40 to 44 of the compensation method.

[0267] To account for detector aging in the phosphor-converted LED scale factors, the white-on-green-detector white-LED scale factor may be divided by the blue-on-green-detector blue-LED scale factor to produce a white-over-blue-on-green scale factor ratio (WoBoG). Similarly, the white-on-red-detector white-LED scale factor may be divided by the blue-on-red-detector blue-LED scale factor to produce a white-over-blue-on-green scale factor ratio (WoBoR). Next, the WoBoR scale factor ratio may be further divided by the WoBoG scale factor ratio to produce a white phosphor to white-blue pump (WPoWB) ratio. The white phosphor to white-blue pump (WPoWB) ratio provides an indication of how the spectrum of the phosphor-converted white LED changes over time, and accounts for any reduction in detector responsiveness that may change over time. In some embodiments, the WPoWB ratio may be used to adjust the overall chromaticity of the phosphor-converted LED. Once the overall chromaticity of the phosphor-converted LED is set, the white-on-red detector scaling factor may be applied in step 62 to the overall expected luminous flux value of the phosphor-converted white LED to account for aging-related lumen changes.

[0268] Compared with conventional compensation methods, Fig.13 The compensation method shown in and described above provides many advantages. As with other methods described herein, Fig.13 The compensation method improves the measurement of the forward voltage of the detector(s) by applying a relatively small drive current (e.g., about 0.1 mA to about 0.3 mA) to the photodetector(s). In addition, Fig.13 The compensation method interpolates between multiple stored photocurrent values ​​obtained at different drive currents and different temperatures, and obtains a nonlinear relationship between the photocurrent and the drive current of each emitting LED at the current operating temperature (Vf_current). This enables the compensation method to accurately and individually characterize the photocurrent to drive current relationship of each individual LED, thereby providing accurate aging compensation for all emitting LEDs included in the lighting device. In addition, the compensation method described herein accounts for both emitter aging and detector aging, and provides compensation for chromaticity shifts that occur when phosphor-converted white emitting LEDs age. Therefore, the compensation method described herein provides accurate control of the luminous flux and chromaticity of individual emitting LEDs over time.

[0269] Exemplary Embodiments of Improved Lighting Devices

[0270] The improved methods described herein for calibrating and controlling lighting devices can be used in substantially any LED lighting device having multiple emitting LEDs and one or more photodetectors. As described in more detail below, the improved methods described herein can be implemented in the form of hardware, software, or a combination of both in the LED lighting device.

[0271] Lighting devices that benefit from the improved methods described herein can have essentially any form factor, including but not limited to parabolic lamps (e.g., PAR 20, 30, or 38), linear lamps, floodlights, and mini reflectors. In some cases, the lighting device can be mounted in the ceiling or wall of a building and can be connected to an AC power source or some other AC power source. However, a skilled artisan will understand how the improved methods described herein can be used in other types of lighting devices powered by other power sources (e.g., batteries or solar energy).

[0272] Now, reference will be made to FIGS. 16 to Fig. 20 While describing exemplary embodiments of improved lighting devices, the figures show different types of LED lighting devices, each of which has one or more emitter modules. Although examples are provided herein, the present invention is not limited to any particular type of LED lighting device or emitter module design. A skilled artisan will understand how the method steps described herein can be applied to other types of LED lighting devices with substantially different emitter module designs.

[0273] Fig.16A is composed of multiple transmitter modules (in Fig.16A A photograph of a linear lamp 70 (not shown) is shown, wherein the plurality of emitter modules are spaced apart from one another and are generally arranged in a straight line. Each emitter module included in the linear lamp 70 includes a plurality of emitting LEDs and at least one dedicated photodetector, all of which are mounted on a common substrate and enclosed within a primary optical structure. The primary optical structure may be formed from a variety of different materials and may have essentially any shape and / or size necessary to shape the light emitted by the emitting LEDs in a desired manner. Although the primary optical structure is described below as a dome, those skilled in the art will understand how the primary optical structure may have essentially any other shape or configuration that encloses the emitting LEDs and the at least one photodetector.

[0274] exist Fig. 16B The following table shows the Fig.16A76. An exemplary emitter module 72 within a linear lamp 70 of FIG. 70. In the illustrated embodiment, the emitter module 72 includes four emission LEDs 74 of different colors arranged in a square array and placed as close together as possible in the center of a primary optical structure (e.g., a dome) 76 so as to approximate a centrally located point source. In some embodiments, each of the emission LEDs 74 can be configured to produce illumination at a different peak emission wavelength. For example, the emission LEDs 74 can include an RGBW LED or an RGBY LED. In addition to the emission LEDs 74, a dedicated photodetector 78 is included within the dome 76 and is arranged somewhere near the periphery of the array. The dedicated photodetector 78 can be any device (e.g., a silicon photodiode or an LED) that produces a current indicative of incident light.

[0275] In at least one embodiment, the photodetector 78 is an LED with a peak emission wavelength in the range of about 550nm to 700nm. A photodetector with such a peak emission wavelength will not generate photocurrent in response to infrared light, which reduces interference from ambient light sources. In at least one preferred embodiment, the photodetector 78 may include a small red, orange, or yellow LED. In some embodiments, a dedicated photodetector 78 may be arranged to capture the maximum amount of light from the emission LEDs with the shortest wavelengths (e.g., blue and green emission LEDs) that are reflected from the surface of the dome 76.

[0276] In some embodiments, the emitter module 72 may include a phosphor-converted white (W) emitting LED 74, and a dedicated photodetector 78 may be used to measure the photocurrent (Iph_d1) induced by light passing through the phosphor portion of the phosphor-converted LED. To measure the photocurrent (Iph_d2) induced by the blue LED portion of the phosphor-converted LED, the green emitting LED 74 may sometimes be configured as an additional photodetector. These photocurrent measurements may be stored in Figure 7 The calibration table is in the Fig.13 The compensation method is used to compensate for the chromaticity shift caused by phosphor aging.

[0277] Fig.17A and Fig. 17B Fundamentally different types of lighting device and emitter module designs are presented. Specifically, Fig.17A Depicted is a lighting device 80 having a parabolic form factor (e.g., PAR 38) and only one emitter module (in Fig.17A ). Since these lighting devices have only one emitter module, the emitter module comprised in such a device usually comprises a plurality of LED chains of different colors, wherein each chain comprises two or more LEDs of the same color. Fig. 17B Demonstrates that can be included in Fig.17A An exemplary emitter module 82 within a PAR lamp 80 is shown in FIG.

[0278] In the illustrated embodiment, the emitter module 82 includes an array of emitting LEDs 84 and a plurality of dedicated photodetectors 88, all of which are mounted on a common substrate and enclosed within a primary optical structure (e.g., a dome) 86. In some embodiments, the array of emitting LEDs 84 may include a number of different colored LED chains, wherein each chain is configured to produce illumination at a different peak emission wavelength. According to one embodiment, the array of emitting LEDs 84 may include a chain of four red LEDs, a chain of four green LEDs, a chain of four blue LEDs, and a chain of four white or yellow LEDs. Each LED chain is coupled in series and driven by the same drive current. In some embodiments, the individual LEDs in each chain may be dispersed about the array and may be arranged so that no color appears twice in any row, column, or diagonal to improve color mixing within the emitter module 82.

[0279] exist Fig. 17B In an exemplary embodiment of the invention, four dedicated photodetectors 88 are included within the dome 86 and are arranged around the periphery of the array. In some embodiments, the dedicated photodetectors 88 may be placed near or in the middle of each edge of the array and may be connected in parallel to a receiver of the lighting device. By connecting the dedicated photodetectors 88 in parallel with the receiver, the photocurrent induced on each photodetector may be summed to minimize spatial variations between similarly colored LEDs that may be dispersed about the array. The dedicated photodetectors 88 may be any device (e.g., a silicon photodiode or an LED) that produces a current indicative of incident light. However, in one embodiment, the dedicated photodetectors 88 are preferably LEDs having a peak emission wavelength in the range of 500nm to 700nm. A photodetector having such a peak emission wavelength will not produce a photocurrent in response to infrared light, which reduces interference from ambient light.

[0280] In at least one preferred embodiment, the emitter module 82 includes a phosphor-converted white (W) emitting LED 84 and two different colored photodetectors to measure different portions of the phosphor-converted LED spectrum. In one example, the dedicated photodetectors 88 may include one or more small red LEDs and one or more small green LEDs. In such an example, the dedicated red photodetector 88 may be used to measure the photocurrent induced by light passing through the phosphor portion of the phosphor-converted LED (Iph_d1), while the dedicated green photodetector 88 may be used to measure the photocurrent induced by light emitted by the blue LED portion of the phosphor-converted LED (Iph_d2). These photocurrent measurements (Iph_d1 and Iph_d2) may be stored in Figure 7 calibration table and can be Fig.13 The compensation method is used to compensate for the chromaticity shift caused by phosphor aging.

[0281] exist Fig.16A and Fig.17A The lighting equipment shown in Fig. 16B and Fig. 17B The emitter modules shown in are provided only as examples of lighting devices in which improved calibration and compensation methods can be used. Further descriptions of these lighting devices and emitter modules can be found in related U.S. Patent Application No. 14 / 097,339 and related U.S. Provisional Patent Application No. 61 / 886,471, which are jointly assigned and incorporated herein by reference in their entirety. However, the inventive concepts described herein are not limited to any particular type of LED lighting device, any particular number of emitter modules that can be included in an LED lighting device, or any particular number, color, or arrangement of emission LEDs and photodetectors that can be included in an emitter module. Instead, the present invention may require only that the LED lighting device include at least one emitter module, the at least one emitter module including a plurality of emission LEDs and at least one dedicated photodetector. In some embodiments, if one or more of the emission LEDs are sometimes configured to provide such a function, then a dedicated photodetector may not be required.

[0282] Fig.18A90 is a side view of an embodiment of an improved emitter module 90 including a plurality of emission LEDs 92 and one or more dedicated photodetectors 94, all of which are mounted on a common substrate 96 and enclosed in a primary optical structure (e.g., a dome) 98. A heat sink 100 is coupled to the bottom surface of the substrate 96 for directing heat away from the heat generating components of the emitter module 90. The heat sink 100 can essentially include any material having a relatively high thermal conductivity and electrical conductivity. In some embodiments, the heat sink 100 is formed of a material having a thermal conductivity ranging between about 200 W / (mK) and about 400 W / (mK). In one embodiment, the heat sink is formed of a copper or copper alloy material, or an aluminum or aluminum alloy material. The heat sink 100 can be a relatively thick layer ranging between about 1 mm and about 10 mm, and in one embodiment, can be about 3 mm thick.

[0283] The emitter module 90 may include substantially any number and color of transmit LEDs 92 and substantially any number and color of dedicated photodetectors 94. In one exemplary embodiment, as in Fig. 16B and Fig. 17B , the emission LED 92 includes one or more red LEDs, one or more blue LEDs, one or more green LEDs, and one or more white or yellow LEDs. The emission LED 92 can be generally arranged near the center of the dome 98, and the dedicated photodetector 94 can be generally arranged near the periphery of the array. In an exemplary embodiment, the dedicated photodetector 94 can include one or more red, orange, yellow and / or green LEDs. The LED used to implement the dedicated photodetector 94 is generally smaller than the emission LED 92 and is generally arranged to capture the maximum amount of light emitted from the emission LED 92 and reflected from the dome 98. In some embodiments, if one or more of the emission LEDs in the emission LED 112 are sometimes configured to detect incident light, the dedicated photodetector 114 can be omitted.

[0284] The primary optical structure 98 can be formed of a variety of different materials and can have substantially any shape and / or size necessary to shape the light emitted by the emission LED in a desired manner. Although the primary optical structure 98 is described herein as a dome, those skilled in the art will understand how the primary optical structure can have substantially any other shape or configuration that encloses the emission LED 92 and the at least one photodetector 94. In some embodiments, the shape, size, and material of the dome 98 can generally be designed to improve optical efficiency and color mixing within the emitter module 90.

[0285] In one embodiment, the substrate 96 may include a laminate material such as a printed circuit board (PCB) FR4 material or a metal clad PCB material. However, in at least one preferred embodiment of the present invention, the substrate 96 may be formed of a ceramic material (or some other reflective material) so that the substrate can generally be used to improve output efficiency by reflecting light out of the emitter module 90. In addition, the substrate 96 can be configured to provide a relatively high thermal impedance or a low thermal impedance in a lateral direction (i.e., a direction in the plane of the substrate). In one embodiment, the substrate 96 may be formed of a material having a thermal conductivity less than or equal to about 150 W / (mK) (e.g., aluminum nitride, AlN). In another embodiment, the substrate 96 may be formed of a material having a thermal conductivity less than about 30 W / (mK) (e.g., aluminum nitride Al2 O3 material), or a material having a thermal conductivity less than about 1 W / (mK) (e.g., a PCB laminate material). The high thermal conductivity or low thermal conductivity provided by the substrate 96 in the lateral direction advantageously isolates the junction temperature of the emission LED 92 and the photodetector 94 and avoids inaccurate Vfe and Vfd measurements.

[0286] In some embodiments, the substrate 96 can be further configured to provide a relatively low thermal impedance or a high thermal impedance in a vertical direction (i.e., a direction perpendicular to the plane of the substrate). Specifically, a relatively low thermal impedance path 102 can be provided between each emitting LED 92 and each photodetector 94 and the heat sink 100. In addition to improving heat dissipation, the low thermal impedance path 102 enables the substrate 96 to maintain a consistent temperature difference between the emitter junction temperature and the detector junction temperature under operating conditions.

[0287] As pointed out above, Figure 8 Alternative embodiments of the temperature compensation method shown in can use the forward voltage (Vfd) measured across the photodetector(s) instead of the forward voltage (Vfe) measured across the emitting LED to provide an indication of the current operating temperature. However, these alternative embodiments indicate that if the temperature difference between the emitting LED and the photodetector(s) remains substantially consistent over the operating temperature range, then only the detector forward voltage (Vfd) can be used.

[0288] Fig.18A The improved emitter module 90 shown in FIG. 1 maintains a relatively fixed temperature difference between the transmit LEDs 92 and the dedicated photodetectors 94 by providing a low thermal impedance path 102 to a heat sink 100 for each of the transmit LEDs 92 and each of the photodetectors 94. This can be accomplished in many different ways. Fig.18AIn the particular embodiment shown in FIG. 1 , a low thermal impedance path 102 is provided by minimizing the thickness of the substrate 96 (which minimizes the vertical distance between the emitting LEDs 92, the photodetectors 94, and the heat sink 100) and by connecting each of the emitting LEDs 92 and each of the photodetectors 94 to the heat sink 100 using a plurality of thermally conductive wires 102. In one example, the thickness (T) of the substrate 96 may range between about 300 μm and about 500 μm.

[0289] Typically, the plurality of heat-conducting wires 102 can include substantially any heat-conducting material. In some embodiments, the heat-conducting wires 102 are formed of a material having a thermal conductivity range between about 200 W / (mK) and about 400 W / (mK). The material used for the heat-conducting wires 102 may be the same as or different from the material used for the heat sink 100. In one embodiment, the heat-conducting wires 102 are formed of aluminum, aluminum alloy, copper, or copper alloy material. The plurality of heat-conducting wires 102 can be formed by drilling vertical holes through the substrate (using mechanical or optical means) and using any appropriate method to fill or plate the holes (or through-holes) with a metal material. In some embodiments, each heat-conducting wire 102 may include a plurality of (e.g., about 10 to 20) dense through-holes, each of which is approximately several hundred microns wide.

[0290] If used in lighting equipment Fig.18A The transmitter module 90 shown in FIG. Figure 8 The detector forward voltage (Vfd) is used within the temperature compensation method of the transmitter to provide a good indication of the junction temperature of the transmit LED 92. Because the temperature difference between the transmit LED 92 and the photodetector 94 is fixed, the detector forward voltage (Vfd) can be used within the temperature compensation method of the transmitter to provide a good indication of the junction temperature of the transmit LED 92. Figure 8 The detector forward voltage (Vfd) is measured in step 38 (not the emitter forward voltage) and can be used using the voltage stored in Figure 7 The emitter forward voltage (Vfe) is calculated using the detector forward voltage (Vfd) measurements and the emitter forward voltage (Vfe) in the calibration table. This will advantageously reduce the need to Figure 8 The number of forward voltage measurements obtained during the temperature compensation method.

[0291] Although attached Fig.18A The emitter module shown in provides the desired thermal characteristics, but it fails to provide adequate thermal isolation between the emitting LED, photodetector, and heat sink. Electrical contacts to the anode, cathode, or both (in a flip-chip LED design) are typically provided on the back side of the LED for both the emitting LED and the photodetector. Fig.18AThe metal wires shown in FIG. 1 are used to connect the contacts directly to the heat sink to electrically couple the contacts to the heat sink. To provide electrical isolation between the LED and the heat sink, the Fig.18B A routing layer is provided in for connecting LED chains together and for connecting the LED anodes / cathodes to external contacts outside the dome.

[0292] Fig.18B is a side view of another embodiment of an improved emitter module 110 including a plurality of transmitting LEDs 92 and one or more dedicated photodetectors 94 all mounted on a common substrate 112 and enclosed within a primary optical structure 98. Fig.18B Many of the components shown in are similar to Fig.18A The same reference numerals are used to denote the same components.

[0293] The emitter module 110 can include substantially any number, color, and arrangement of emission LEDs 92 and substantially any number, color, and arrangement of dedicated photodetectors 94. The emission LEDs 92 and dedicated photodetectors 94 can be similar to those described above, but are not limited to those. In some embodiments, if one or more of the emission LEDs 92 are sometimes configured to detect incident light, one or more of the dedicated photodetectors 94 can be omitted.

[0294] The primary optical structure 98 may be formed from a variety of different materials and may have substantially any shape and / or size necessary to shape the light emitted by the emission LED 92 in a desired manner. Although the primary optical structure 98 is described herein as a dome, those skilled in the art will understand how the primary optical structure may have substantially any other shape or configuration that encloses the emission LED 92 and the at least one photodetector 94. In some embodiments, the shape, size, and material of the dome 98 may be generally designed to improve optical efficiency and color mixing within the emitter module 110.

[0295] The heat sink 100 is coupled to the bottom surface of the substrate 112 for directing heat away from the heat generating components of the transmitter module 110. The heat sink 100 can basically include any material with relatively high thermal conductivity and electrical conductivity. In some embodiments, the heat sink 100 is formed of a material having a thermal conductivity ranging between about 200W / (mK) and about 400W / (mK). In one embodiment, the heat sink is formed of a copper or copper alloy material, or an aluminum or aluminum alloy material. In some embodiments, the heat sink 100 can be a relatively thick layer ranging between about 1mm and about 10mm, and in one embodiment, can be about 3mm thick.

[0296] Transmitter module 110 differs from transmitter module 90 in at least one respect: the electrical contacts of the transmit LED 92 and the photodetector 94 are electrically isolated from the heat sink 100. Fig.18B This is achieved in the embodiment of the present invention by utilizing a substrate 112 having multiple layers. Although the overall thickness of the multi-layer substrate 112 (e.g., about 300 μm to about 500 μm) can be similar to Fig.18A , but in some embodiments, Fig.18B The multi-layer substrate 112 shown in FIG. 1 is generally formed to include multiple routing layers and dielectric layers that not only provide electrical isolation between the electrical contacts of the LED and the heat sink, but also improve routing flexibility.

[0297] According to one embodiment, the multilayer substrate 112 may include a first routing layer 114, a first dielectric layer 116, a second routing layer 118, and a second dielectric layer 120. The first routing layer 114 may be coupled to electrical contacts of the emitting LED 92 and one or more photodetectors 94, and may be formed on the first dielectric layer 116. The first routing layer 114 may have a thickness ranging between about 10 μm and about 20 μm, may be formed of a material having a thermal conductivity ranging between 200 W / (mK) and about 400 W / (mK) (e.g., copper or aluminum material, or alloys thereof), and may be formed on the upper surface of the first dielectric layer 116 by any well-known process. For example, the first routing layer 114 may be formed by printing or depositing metal lines on the upper surface of the first dielectric layer 116.

[0298] The first dielectric layer 116 is sandwiched between the first routing layer 114 and the second routing layer 118 to electrically isolate the electrical contacts of the LED from the heat sink 100. In some embodiments, the first dielectric layer 116 may be a relatively thin layer having a thickness between about 10 μm and about 100 μm, and may be formed of a dielectric material having a relative dielectric constant ranging between about 3 and 12. In one example, the first dielectric layer 116 may be formed of an aluminum nitride material or an aluminum oxide material, but is not limited to such materials.

[0299] In addition to providing electrical isolation, the first dielectric layer 116 provides relatively high thermal impedance in the lateral direction by using a relatively low thermal conductivity (which is less than about 150 W / (mK)) and keeping the thickness of the layer small relative to the spacing between the emitting LED and the photodetector. In an exemplary embodiment, the first dielectric layer 116 can have a thickness of about 30 μm and can separate the emitting LED 92 and the photodetector 94 by at least 200 to 300 μm on the upper surface of the substrate 112. Such an embodiment will provide a thermal conductivity in the vertical direction that is at least 10 times higher than the thermal conductivity provided in the lateral direction.

[0300] The second routing layer 118 is coupled between the first dielectric layer 116 and the second dielectric layer 120, and is generally configured to route signals between the first routing layer 114 and an external electrical contact (not shown) arranged outside the main optical structure. Like the first routing layer 114, the second routing layer 118 can have a thickness ranging from about 10 μm to about 20 μm, can be formed of a material having a thermal conductivity ranging from 200 W / (mK) to about 400 W / (mK) (e.g., copper or aluminum materials, or alloys thereof), and can be formed on the upper surface of the second dielectric layer 120 by any well-known process. For example, the second routing layer 118 can be formed by printing or depositing metal lines on the upper surface of the second dielectric layer 120. In order to route signals between the first routing layer 114 and the second routing layer 118, through holes 124 can be formed in the first dielectric layer 116. These through holes can be formed according to any known process.

[0301] In some embodiments, the second dielectric layer 120 may be coupled between the second routing layer 118 and the heat sink 100, and may generally be configured to provide a relatively high thermal impedance in the lateral direction and a relatively low thermal impedance in the vertical direction. In some embodiments, the second dielectric layer 120 may be a relatively thick layer having a thickness between about 100 μm and about 1000 μm, which imparts stiffness to the transmitter module 110. In some embodiments, the second dielectric layer 120 may be formed of a dielectric material having a relative dielectric constant ranging between about 3 and 12 and a thermal conductivity less than about 150 W / (mK). In one example, the second dielectric layer 120 may be formed of an aluminum nitride material or an aluminum oxide material, but is not limited to such materials.

[0302] The second dielectric layer 120 is similar to Fig.18A , because the second dielectric layer uses a material with a thermal conductivity of less than about 150W / (mK) to implement the second dielectric layer 120, a relatively high thermal impedance is provided in the lateral direction, and a relatively low thermal impedance is provided in the vertical direction by including a plurality of heat conductive wires 122, which extend vertically through the second dielectric layer 120 between the second routing layer 118 and the heat sink 100. As noted above, the plurality of heat conductive wires 122 may be formed of a material having a thermal conductivity ranging between about 200W / (mK) and about 400W / (mK) (e.g., copper or aluminum material, or alloys thereof). The plurality of heat conductive wires 122 may be formed by drilling vertical holes (using mechanical or optical means) through the second dielectric layer and using any appropriate method to fill or plate the holes (or through holes) with an appropriate metal material. In some embodiments, each heat conductive wire 122 may include a plurality of (e.g., about 10 to 20) dense through holes, each of which is several hundred microns wide.

[0303] In some embodiments, the third routing layer 126 may be coupled between the second dielectric layer 120 and the heat sink 100. Unlike the first and second routing layers (which include metal lines printed on the first and second dielectric layers), the third routing layer 126 may extend substantially continuously across the upper surface of the heat sink 100 to improve thermal contact between the plurality of thermally conductive lines 122 and the heat sink 100 and improve heat dissipation thereon.

[0304] picture Fig.18A Like the substrate 96 shown in FIG. Fig.18B The multilayer substrate 112 shown in FIG. 1 provides good thermal isolation between the emitting LEDs 92 and between the emitting LEDs and the photodetectors while providing stiffness and maintaining good overall thermal conductivity to the heat sink 100. This allows for Figure 8 The detector forward voltage (Vfd) measurement is used in the compensation method instead of the emitter forward voltage (Vfe) measurement, which reduces the number of forward voltage measurements that need to be obtained during the compensation method.

[0305] Fig.18B The multilayer substrate 112 shown in FIG. 1 also provides other advantages that are not provided by the single layer substrate 96. For example, the substrate 112 includes multiple routing layers and dielectric layers that provide routing flexibility for connecting the emission LED 92 chain together and provide electrical isolation between the electrical contacts of the emission LED and the photodetector and the heat sink 100.

[0306] In alternative embodiments of the present invention, the multilayer substrate 112 may also be implemented in a somewhat different manner. For example, instead of using a dielectric material or a ceramic material for layers 116 and 120, these layers may use a laminate material such as a printed circuit board (PCB) FR4 material or a metal clad PCB material. However, because the thermal conductivity of the laminate material is much less than the thermal conductivity of the ceramic material (e.g., less than about 1 W / (mK)), using a laminate material instead of a ceramic material will reduce the thermal conductivity of layer 120. Regardless of the material used for layer 120, thermal conductivity can be increased in some embodiments of the present invention by increasing the number of thermal conductive lines 122 included below the LED array. Although this approach will provide better overall thermal conductivity from the LED array to the heat sink, it will provide poorer thermal separation between the emitting LEDs.

[0307] Fig.19 is an example of a block diagram of a lighting device 110 that is configured to accurately maintain a desired luminous flux and a desired chromaticity over variations in drive current, temperature, and time. Fig.19 The lighting device shown in the figure provides a lighting device that can be used to implement Figure 6 The calibration method shown in Figure 8and Fig.13 An example of hardware and / or software of the compensation method is shown in FIG.

[0308] In the illustrated embodiment, the lighting device 110 includes a plurality of transmitting LEDs 126 and one or more dedicated photodetectors 128. In this example, the transmitting LEDs 126 include four chains of any number of LEDs. In a typical embodiment, each chain has 2 to 4 LEDs of the same color, which are coupled in series and configured to receive the same drive current. In one example, the transmitting LEDs 126 can include a red LED chain, a green LED chain, a blue LED chain, and a white or yellow LED chain. However, the present invention is not limited to any particular number of LED chains, any particular number of LEDs within a chain, or any particular color or combination of LED colors.

[0309] Although one or more dedicated photodetectors 128 are Fig.19 , but the invention is not limited to any particular type, number, color, combination or arrangement of photodetectors. Fig. 16B As discussed above, one or more dedicated photodetectors 128 may include a small red, orange, or yellow LED. Fig. 17B As discussed above, the one or more dedicated photodetectors 128 may include one or more small red LEDs or one or more small green LEDs. In some embodiments, if one or more of the emission LEDs 126 are sometimes configured to function as photodetectors, then the dedicated photodetectors 128 may be omitted. Fig.19 One or more of the dedicated photodetectors 128 shown in . As discussed above, multiple emission LEDs 126 and (optional) dedicated photodetectors 128 may be included in an emitter module. As discussed above, in some embodiments, a lighting device may include more than one emitter module.

[0310] In addition to including one or more emitter modules, the lighting device 110 includes various hardware and software components configured to power the lighting device and control the light output from the (multiple) emitter modules. In one embodiment, the lighting device is connected to an AC power source 112 and includes an AC / DC converter 114 for converting the AC power (e.g., 120V or 240V) into a DC voltage (VDC). As shown in Fig.19As shown in FIG. 1 , this DC voltage (e.g., 15V) is supplied to an LED driver and receiver circuit 124 to generate an operating drive current that is applied to a transmitting LED 126 to generate illumination. In addition to the AC / DC converter, a DC / DC converter 116 is included for converting the DC voltage VDC (e.g., 15V) to a lower voltage VL (e.g., 3.3V) that is used to power low voltage circuits included in the lighting device (e.g., PLL 118, wireless interface 120, and control circuit 122).

[0311] In the illustrated embodiment, the PLL 118 locks to the AC power frequency (e.g., 50 or 60 Hz) and generates a high-speed clock (CLK) signal and a synchronization signal (SYNC). The CLK signal provides timing for the control circuit 122 and the LED driver and receiver circuit 124. In one example, the CLK signal frequency is in the tens of mHz range (e.g., 23 MHz) and is precisely synchronized with the AC power frequency and phase. The SNYC signal is used by the control circuit 122 to create timing for obtaining the various optical and electrical measurements described above. In one example, the SNYC signal frequency is equal to the AC power frequency (e.g., 50 or 60 Hz) and is also precisely phase aligned with the AC power.

[0312] In some embodiments, a wireless interface 120 may be included and may be used to calibrate the lighting device 110 during manufacture. As noted above, for example, an external calibration tool (in Fig.19 The control circuit 122 may communicate the luminous flux and chromaticity calibration values ​​to the lighting device under test via the wireless interface 120. For example, the calibration values ​​received via the wireless interface 120 may be stored in a calibration value table in the storage medium 121 of the control circuit 122. In some embodiments, the control circuit 122 may use the calibration values ​​to generate calibration coefficients stored in the storage medium 121 in addition to or in place of the received calibration values.

[0313] The wireless interface 120 is not limited to receiving only calibration data, and can be used to communicate information and commands for many other purposes. For example, the wireless interface 120 can be used during normal operation to communicate commands that can be used to control the lighting device 110 or to obtain information about the lighting device 110. For example, a command can be communicated to the lighting device 110 via the wireless interface 120 to turn the lighting device on / off, control the dimming level and / or color set point of the lighting device, initiate a calibration procedure, or store calibration results in a memory. In other examples, the wireless interface 120 can be used to obtain status information or fault status codes associated with the lighting device 110.

[0314] In some embodiments, the wireless interface 120 may operate according to ZigBee, WiFi, Bluetooth, or any other proprietary or standard wireless data communication protocol. In other embodiments, the wireless interface 120 may communicate using radio frequency (RF), infrared (IR) light, or visible light. In alternative embodiments, a wired interface may be used in place of the wireless interface 120 to communicate information, data, and / or commands via an AC power source, a dedicated conductor, or a set of conductors.

[0315] Using the timing signals received from the PLL 118, the control circuit 122 calculates and generates values ​​indicative of the desired drive current to be used for each transmit LED chain 126. For example, such information may be communicated from the control circuit 122 to the LED driver and receiver circuit 124 via a standards-compliant serial bus such as SPI or I2 C. In addition, the control circuit 122 may provide a latch signal that instructs the LED driver and receiver circuit 124 to simultaneously change the drive current supplied to each of the LEDs 126, thereby preventing brightness and color artifacts.

[0316] Typically, the control circuit 122 may be configured to Figure 8 and Fig.13 The control circuit 122 may determine the corresponding driving current required to achieve the desired luminous flux and / or desired chromaticity of the lighting device by using one or more of the compensation methods shown in and described above. In some embodiments, the control circuit 122 may determine the corresponding driving current by executing program instructions stored in the storage medium 121. In some embodiments, the storage medium may be a non-volatile memory and may be configured to store the program instructions together with the calibration value table (e.g., the above description of Figure 7 Alternatively, the control circuit 122 may include combinatorial logic for determining the desired drive current, and the storage medium 121 may only be used to store the calibration value table.

[0317] Typically, the LED driver and receiver circuit 124 may include a number (N) of driver blocks 130 equal to the number of transmit LED chains 126 included in the lighting device. In the exemplary embodiment discussed herein, the LED driver and receiver circuit 124 includes four driver blocks 130, each of which is configured to produce illumination from a different transmit LED chain in the transmit LED chains 126. The LED driver and receiver circuit 124 also includes circuitry required to measure ambient temperature (optional), detector and / or emitter forward voltage, and detector photocurrent, and adjust the LED drive current accordingly. Each driver block 130 receives data indicating a desired drive current from the control circuit 122, as well as a latch signal indicating when the driver block 130 should change the drive current.

[0318] Fig. 20 is an exemplary block diagram of an LED driver and receiver circuit 124 according to one embodiment of the present invention. Fig. 20 As shown in FIG. 1 , the LED driver and receiver circuit 124 includes four driver blocks 130, each of which includes a buck converter 132, a current source 134, and an LC filter 138 for generating a drive current applied to the connected transmitting LED chain 126a to produce illumination and obtain a forward voltage (Vfe) measurement result. In some embodiments, when the controller 154 drives the "output_enable" signal high, the buck converter 132 can generate a pulse width modulated (PWM) voltage output (Vdr). This voltage signal (Vdr) is filtered by the LC filter 138 to generate a forward voltage on the anode of the connected LED chain 126a. The cathode of the LED chain is connected to the current source 134, which forces a fixed drive current equal to the value provided by the "transmitter current" signal through the LED chain 126a when the "Led_on" signal is high. The "Vc" signal from the current source 134 provides feedback to the buck converter 132 to output the appropriate duty cycle and minimize the voltage drop across the current source 134.

[0319] like Fig. 20 As shown in FIG. 1 , each driver block 130 includes a differential amplifier 137 for measuring a forward voltage drop (Vfe) across the transmit LED chain 126a. When measuring Vfe, the buck converter 132 is turned off, and the current source 134 is configured to pull a relatively small drive current (e.g., approximately 1 mA) through the connected transmit LED chain 126a. The voltage drop (Vfe) generated by this current across the LED chain 126a is measured by the differential amplifier 137. The differential amplifier 137 generates a signal equal to the forward voltage (Vfe) drop across the transmit LED chain 126a during the forward voltage measurement.

[0320] As noted above, some embodiments of the present invention sometimes use one of the emission LEDs (e.g., a green emission LED) as a photodetector. In such embodiments, when the emission LED is configured to detect incident light, the driver block 130 may include additional circuitry for measuring the photocurrent (Iph_d2) induced across the emission LED. For example, each driver block 130 may include a transimpedance amplifier 135, which is typically used to convert an input current into an output voltage proportional to a feedback resistor. Fig. 20As shown in FIG. 1 , the positive terminal of the transimpedance amplifier 135 is connected to the Vdr output of the buck converter 132, and the negative terminal is connected to the cathode of the last LED in the LED chain 126 a. When the “LED_ON” signal is low, the transimpedance amplifier 135 is enabled. When the “LED_ON” signal is high, the output of the transimpedance amplifier 135 is tri-stated.

[0321] When measuring the photocurrent (Iph_d2) induced by the emitting LED, the buck converter 132 connected to all other emitting LEDs should be turned off to avoid visual artifacts caused by LED current transients. In addition, the buck converter 132 coupled to the emitting LED under test should also be turned off to prevent switching noise within the buck converter from interfering with the photocurrent measurement. Although the buck converter is turned off, the Vdr output of the buck converter 132 coupled to the emitting LED under test is maintained at a specific value (e.g., approximately 2-3.5 volts multiplied by the number of emitting LEDs in the chain) through the capacitor in the LC filter 138. When this voltage (Vdr) is applied to the anode of the emitting LED under test and the positive terminal of the transimpedance amplifier 135, the transimpedance amplifier produces an output voltage (relative to Vdr) that is applied to the positive terminal of the differential amplifier 136. The differential amplifier 136 compares the output voltage of the transimpedance amplifier 135 with Vdr and generates a differential signal corresponding to the photocurrent (Iph_d2) induced across the LED chain 126a.

[0322] In addition to including a plurality of driver blocks 130, the LED driver and receiver circuit 124 may include one or more receiver blocks 140 for measuring the forward voltage (Vfd) and the photocurrent (Iph_d1 or Iph_d2) induced across one or more dedicated photodetectors 128. Fig. 20 Only one receiver block 140 is shown in FIG. 1 , but the LED driver and receiver circuit 124 may generally include a number of receiver blocks 140 equal to the number of dedicated photodetectors included within the transmitter module.

[0323] In the illustrated embodiment, the receiver block 140 includes a voltage source 142 coupled to supply a DC voltage (Vdr) to the anode of a dedicated photodetector 128 coupled to the receiver block, while the cathode of the photodetector 128 is connected to a current source 144. When the photodetector 128 is configured to obtain a forward voltage (Vfd), the controller 154 supplies a "detector on" signal to the current source 144, which forces a fixed drive current (Idrv) through the photodetector 128 that is equal to the value provided by the "detector current" signal.

[0324] When the detector forward voltage (Vfd) measurement result is obtained, the current source 144 is configured to pull a relatively small amount of drive current (Idrv) through the photodetector 128. The voltage drop (Vfd) generated by this current across the photodetector 128 is measured by the differential amplifier 147, which produces a signal equal to the forward voltage (Vfd) drop across the photodetector 128. As noted above, the drive current (Idrv) forced through the photodetector 128 by the current source 144 is typically a relatively small non-operating drive current. In an embodiment where four dedicated photodetectors 128 are coupled in parallel, the non-operating drive current can be approximately 1 mA. However, smaller / larger drive currents can be used in embodiments including a fewer / greater number of photodetectors, or in embodiments where the photodetectors are not connected in parallel.

[0325] Similar to the driver block 130, the receiver block 140 also includes a circuit for measuring the photocurrent (Iph_d1 or Iph_d2) induced on the photodetector 128 by the light emitted by the transmitting LED. Fig. 20 As shown in , the positive terminal of the transimpedance amplifier 145 is coupled to the Vdr output of the voltage source 142, and the negative terminal is connected to the cathode of the photodetector 128. When connected in this manner, the transimpedance amplifier 145 produces an output voltage relative to Vdr (e.g., about 0 to 1V), which is supplied to the positive terminal of the differential amplifier 146. The differential amplifier 146 compares the output voltage to Vdr and generates a differential signal corresponding to the photocurrent (Iph_d1 or Iph_d2) induced across the photodetector 128. When the "detector_on" signal is low, the transimpedance amplifier 145 is enabled. When the "detector_on" signal is high, the output of the transimpedance amplifier 145 is tri-stated.

[0326] As noted above, some embodiments of the present invention may disperse individual LEDs within each LED chain 126 around the LED array so that no two LEDs of the same color exist in any row, column, or diagonal (see, e.g., Fig. 17B By connecting multiple dedicated photodetectors 128 in parallel with the receiver block 140, the photocurrent (Iph_d1 or Iph_d2) induced by a given color LED on each photodetector 128 can be summed to minimize spatial variations between similarly colored LEDs dispersed about the array.

[0327] like Fig. 20As shown in , the LED driver and receiver circuit 124 may also include a multiplexer (Mux) 150, an analog-to-digital converter (ADC) 152, a controller 154, and an optional temperature sensor 156. In some embodiments, the multiplexer 150 may be coupled to receive the emitter forward voltage (Vfe) and (optional) photocurrent (Iph_d2) measurements from the driver block 130, and the detector forward voltage (Vfd) and detector photocurrent (Iph_d1 and / or Iph_d2) measurements from the receiver block 140. The ADC 152 digitizes the emitter forward voltage (Vfe) and optional photocurrent (Iph_d2) measurements output from the driver block 130, and the detector forward voltage (Vfd) and detector photocurrent (Iph_d1 and / or Iph_d2) measurements output from the receiver block 140, and provides the results to the controller 154. Fig. 20 As shown in , the controller 154 determines when the forward voltage and photocurrent measurements are obtained and generates an output enable, emitter current, and LED on signal supplied to the driver block 130 and a detector current and detector_on signal supplied to the receiver block 140.

[0328] In some embodiments, the LED driver and receiver circuit 124 may include an optional temperature sensor 156 for obtaining ambient temperature (Ta) measurements. In such embodiments, a multiplexer 150 may also be coupled to multiplex the ambient temperature (Ta) and the forward voltage and photocurrent measurements sent to the ADC 152. In some embodiments, the temperature sensor 156 may be a thermistor and may be included on the driver circuit chip to measure the ambient temperature around the LED or the temperature of a heat sink from the transmitter module. In other embodiments, the temperature sensor 156 may be an LED that functions as both a temperature sensor and an optical sensor to measure ambient light conditions or output characteristics of the LED transmit chain 126. If the optional temperature sensor 156 is included, the output of the temperature sensor may be used in some embodiments to determine if the LED is in a state of light or current flowing through the LEDs. Figure 8 In step 32, whether a significant change in temperature is detected.

[0329] Now refer to Fig.19 and Fig. 20 One embodiment of an improved lighting device 110 is described. Further description of such lighting devices can be found in commonly assigned U.S. Patent Serial Nos. 13 / 970,944, 13 / 970,964 and 13 / 970,990. A skilled artisan will understand how the lighting device can be implemented in alternative ways within the scope of the present invention.

[0330] Those skilled in the art who have the benefit of this disclosure will appreciate that the present invention is believed to provide improved lighting devices and improved methods for calibrating and stepping individual LEDs in lighting devices so as to maintain a desired luminous flux and a desired chromaticity as drive current, temperature, and time vary. In addition, emitter modules with improved thermal and electrical characteristics are provided herein. In view of this specification, further modifications and alternative embodiments of various aspects of the present invention will be apparent to those skilled in the art. Therefore, the following claims are intended to be interpreted as covering all such modifications and variations, and accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive.

Claims

1. A lighting device, comprising: a plurality of light emitting diode (LED) chains configured to generate illumination for the lighting device; an LED driver and receiver circuit configured to substantially continuously apply a drive current to the plurality of LED chains to produce the illumination; a photodetector configured to detect the illumination generated by the plurality of LED chains; a storage medium configured to store a calibration value table that relates a forward voltage and a photocurrent previously measured from the photodetector to a drive current previously applied to each of the LED chains at a plurality of different temperatures during calibration of the lighting device; as well as a control circuit coupled to the LED driver and receiver circuit, the photodetector, and the storage medium, wherein the control circuit is configured to determine an expected photocurrent value for each LED chain from a stored table of calibration values ​​using a current temperature measurement and the drive current currently applied to each LED chain.

2. The lighting device according to claim 1, wherein: The LED driver and receiver circuit is further configured to: measuring a photocurrent induced on the photodetector in response to the illumination generated by each LED chain, one LED chain at a time, and received by the photodetector; measuring a forward voltage generated across the photodetector to provide the current temperature measurement; as well as The measured photocurrent and the measured forward voltage are supplied to the control circuit.

3. The lighting device according to claim 2, wherein: For each LED chain, the control circuit is further configured to: if the expected photocurrent value determined by the control circuit for the LED chain is different from the photocurrent measured by the LED driver and receiver circuit for the LED chain, adjust the drive current currently applied to the LED chain by the LED driver and receiver circuit to generate lighting.

4. The lighting device according to claim 3, wherein: For each LED chain, the control circuit is further configured to: calculating a scaling factor by dividing the expected photocurrent value by the photocurrent measured by the driver circuit; applying the scaling factor to the desired luminous flux value to obtain an adjusted luminous flux value; as well as The driving current currently applied to the LED chain is adjusted so as to achieve the adjusted luminous flux value.

5. The lighting device according to claim 2, wherein: For each LED chain, the control circuit is configured to determine the expected photocurrent value using: the forward voltage measured by the LED driver and receiver circuit, the drive current currently applied by the LED driver and receiver circuit to the LED chain to produce illumination, the calibration value table, and one or more interpolation techniques.

6. The lighting device according to claim 5, wherein: For each LED chain, the calibration value table includes: a first plurality of stored photocurrent values, the first plurality of stored photocurrent values ​​previously obtained from the photodetector after receiving illumination from the LED chain while the LED chain was subjected to a first temperature and a plurality of drive currents were sequentially applied to the LED chain; a second plurality of stored photocurrent values ​​previously obtained from the photodetector after receiving illumination from the LED chain while the LED chain was subjected to a second temperature and the plurality of drive currents were continuously applied to the LED chain; and A plurality of stored forward voltage values ​​are previously measured across the photodetector after obtaining each of the first and second plurality of photocurrents.

7. The lighting device according to claim 6, wherein: The first plurality of stored photocurrent values, the second plurality of stored photocurrent values, and the plurality of stored forward voltage values ​​include measured values ​​or calculated coefficients.

8. The lighting device according to claim 6, wherein: For each LED chain, the control circuit is configured to determine the expected photocurrent value of the LED by: calculating a third plurality of photocurrent values ​​corresponding to the forward voltage measured by the LED driver and receiver circuit by interpolating between the first plurality of stored photocurrent values ​​corresponding to the LED chain and the second plurality of stored photocurrent values; generating a relationship between the third plurality of photocurrent values; as well as The expected photocurrent value corresponding to the drive current currently applied to the LED string by the LED driver and receiver circuit is selected from the generated relationship.

9. The lighting device according to claim 8, wherein: The control circuit is configured to calculate the third plurality of photocurrent values ​​by interpolating between the first and second plurality of stored photocurrent values ​​using a non-linear interpolation technique.

10. The lighting device according to claim 8, wherein: The control circuit is configured to generate the relationship by applying a higher order interpolation to the third plurality of photocurrent values ​​so as to generate a non-linear relationship between the photocurrent and the drive current of the LED chain.

11. The lighting device according to claim 8, wherein: The control circuit is configured to generate the relationship by applying a piecewise linear interpolation to the third plurality of photocurrent values ​​so as to approximate a non-linear relationship between a photocurrent and a drive current of the LED chain.

12. A lighting device comprising: a phosphor-converted LED configured to emit illumination for the lighting device, wherein a spectrum of the illumination includes a first portion having a first peak emission wavelength and a second portion having a second peak emission wavelength different from the first peak emission wavelength; a first photodetector having a detection range configured to detect only the first portion of the spectrum emitted by the phosphor-converted LED; and A second photodetector having a detection range configured to detect only the second portion of the spectrum emitted by the phosphor-converted LED.

13. The lighting device according to claim 12, wherein: The first peak emission wavelength ranges between about 400 nm and about 500 nm, and the second peak emission wavelength ranges between about 500 nm and about 650 nm.

14. The lighting device according to claim 12, wherein: The detection range of the first photodetector is between about 400 and about 500 nm, and the detection range of the second photodetector is between about 500 nm and about 650 nm.

15. The lighting device of claim 12, further comprising an LED driver and receiver circuit configured to: When the lighting device is subjected to a first ambient temperature, sequentially applying a plurality of different drive currents to the phosphor-converted LED to produce illumination at different brightness levels; measuring a photocurrent induced on the first photodetector and the second photodetector by the illumination generated by the phosphor-converted LED at each of the different drive currents; measuring a forward voltage generated across the first photodetector and the second photodetector before, during, or after measuring each induced photocurrent; as well as Repeating the following steps: successively applying a plurality of different drive currents to the phosphor-converted LED; measuring photocurrents induced on the first photodetector and the second photodetector; and measuring a forward voltage generated across the first photodetector and the second photodetector when the lighting device is subjected to a second ambient temperature different from the first ambient temperature.

16. A lighting device comprising one or more emitter modules, wherein: Each transmitter module includes: a plurality of light emitting diodes (LEDs) configured to generate illumination for the lighting device; one or more photodetectors configured to detect illumination generated by the plurality of LEDs; a substrate on which the plurality of LEDs and the one or more photodetectors are mounted, wherein the substrate is configured to provide a relatively high thermal impedance in a lateral direction and a relatively low thermal impedance in a vertical direction; and A primary optical structure is coupled to the substrate for enclosing the plurality of LEDs and the one or more photodetectors within the primary optical structure.

17. The lighting device according to claim 16, wherein: The substrate is formed of a material that provides relatively high thermal resistance in the lateral direction.

18. The lighting device according to claim 17, wherein: The substrate is formed of a material having a thermal conductivity of less than about 150 W / (mK).

19. The lighting device according to claim 17, wherein: The substrate is formed of an aluminum nitride material, an aluminum oxide material, or a laminated material.

20. The lighting device of claim 16, wherein: The thickness of the substrate ranges between about 300 μm and about 500 μm.

21. The lighting device of claim 16, wherein: Each transmitter module includes a heat sink coupled to a bottom surface of the substrate.

22. A lighting device comprising one or more emitter modules, wherein: Each transmitter module includes: a plurality of light emitting diodes (LEDs) configured to generate illumination for the lighting device; one or more photodetectors configured to detect illumination generated by the plurality of LEDs; a multi-layer substrate on which the plurality of LEDs and the one or more photodetectors are mounted; a primary optical structure coupled to the top surface of the multilayer substrate for enclosing the plurality of LEDs and the one or more photodetectors within the primary optical structure; and a heat sink coupled to a bottom surface of the multilayer substrate; and Wherein, the multi-layer substrate comprises: a first routing layer coupled to electrical contacts of the plurality of LEDs and the one or more photodetectors; a first dielectric layer coupled to a bottom surface of the first routing layer and configured to provide electrical isolation between the electrical contacts and the heat sink; a second routing layer coupled to a bottom surface of the first dielectric layer and configured to route signals between the first routing layer and an external electrical contact disposed outside the primary optical structure; and A second dielectric layer is coupled to a bottom surface of the second routing layer and is configured to provide a relatively high thermal impedance in a lateral direction and a relatively low thermal impedance in a vertical direction.

23. The lighting device of claim 22, wherein: The plurality of LEDs includes at least four LEDs mounted close together on the multilayer substrate and arranged in an array near a center of the primary optical structure.

24. The lighting device of claim 22, wherein: The plurality of LEDs include a red LED, a green LED, a blue LED, and a white or yellow LED.

25. The lighting device of claim 24, wherein: The one or more photodetectors include a red LED, an orange LED, or a yellow LED.

26. The lighting device of claim 22, wherein: The plurality of LEDs include a red LED chain, a green LED chain, a green LED chain, and a white or yellow LED chain, and wherein each chain includes two to four LEDs of the same color.

27. The lighting device of claim 26, wherein: The one or more photodetectors include one or more red LEDs and one or more green LEDs.

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