LED lighting device and method of operating the same

Abstract

A light emitting diode (LED)-based lighting device, arranged to emit colored light, wherein the LED-based lighting device comprises: a first LED channel, comprising at least one LED arranged to emit light of a first color; a second LED channel, comprising at least one LED arranged to emit light of a second color, the second color being different from the first color; a controller, arranged to activate the first LED channel and the second LED channel based on a color ratio, so that the LED-based lighting device emits light of a specific color, wherein the controller is also arranged to correct the color ratio based on aging of the at least one LED in the first LED channel and aging of the at least one LED in the second LED channel, thereby ensuring color consistency of the specific color of the LED-based lighting device over time.

Description

Technical Field

[0001] The present disclosure relates to a light emitting diode (LED) based lighting device for emitting light of a specific color, wherein the LED based lighting device comprises at least two LED channels, wherein each LED channel is arranged to emit light of a specific color. Background Art

[0002] Lighting devices utilizing light emitting diodes (LEDs) have been developed for various lighting applications. Due to their long life and high energy efficiency, LED lamps are now also designed to replace conventional fluorescent lamps, i.e. for retrofit applications. For such applications, the retrofit LED lamp is usually adapted to fit into a socket of a corresponding lamp fixture to be retrofitted. Furthermore, since maintenance of the lamp is usually performed by the user, the retrofit LED lamp should ideally be easy to operate with any type of suitable fixture without requiring rewiring of the fixture.

[0003] The present disclosure relates to a lighting device based on multi-channel LEDs. Each channel may include one or more LEDs capable of emitting light of a specific color. For example, the first channel may be related to emitting red light. The second channel may be related to emitting green light, and the third channel may be related to emitting blue light.

[0004] More specifically, the present disclosure may be particularly applicable to LED-based lighting devices having two LED channels, wherein a first LED channel is directed to emitting warm white light and a second LED channel is directed to emitting cool white light.

[0005] Often, such LED based lighting devices are provided with a current source, wherein the LED based lighting device comprises a current splitter for splitting the current onto different channels.

[0006] More specifically, there are often available controllers with multiple LED channels, where each channel is arranged with a switch, where each of the switches is thereby arranged to enable a specific corresponding channel. For example, a first switch may enable a red channel, a second switch may enable a green channel, a third switch may enable a blue channel, and so on.

[0007] A pulse width modulated PWM signal with a specific duty cycle can be provided to the switch. The frequency of the PWM signal should be chosen so that it exceeds the refresh rate of the human eye. This will prevent the user from seeing any flickering. By controlling the duty cycle, the contribution of each of the channels to the total amount of light emitted can be controlled, and thereby the color of the light emitted by the LED-based lighting device can also be controlled. Summary of the invention

[0008] It is an object of the present disclosure to provide an LED based lighting device arranged to emit light of a specific color and arranged to ensure color consistency of the light of the specific color over time.

[0009] In a first aspect, there is provided a light emitting diode (LED) based lighting device arranged to emit colored light, wherein the LED based lighting device comprises:

[0010] - a first LED channel comprising at least one LED arranged to emit light of a first color;

[0011] - a second LED channel comprising at least one LED arranged to emit light of a second color, said second color being different from said first color;

[0012] - a controller arranged for activating the first LED channel and the second LED channel based on a color ratio such that the LED based lighting device emits light having a specific color.

[0013] The controller is further arranged to correct the color ratio based on aging of the at least one LED in the first LED channel and aging of the at least one LED in the second LED channel to ensure color consistency of the specific color of the LED-based lighting device over time.

[0014] The inventors' insight is that different types of LEDs may degrade differently over time. For example, warm white LEDs may degrade faster over time than cool white LEDs, or vice versa. This may affect not only the intensity of light emitted by an LED-based lighting device, but also the color of the LED-based lighting device. The present disclosure is directed to the latter.

[0015] This can be explained as follows. Typically, a controller may use a certain set point for a specific color of light. This set point determines the ratio between different LED channels. For example, a first LED channel may be active 60% of the time, and a second LED channel may be active 75% of the time. The combination of the two LED channels results in a specific light being emitted. The inventors have discovered that the LEDs in the first channel may degrade differently over time than the LEDs in the second channel. As such, the ratio (i.e., 60% vs. 75%) is also corrected based on this specific degradation effect.

[0016] According to the present disclosure, the above is summarized as the aging of the LED. Therefore, the aging of the LED may result in less light being emitted, or even in a color shift of the emitted light. Both of these can be taken into account when correcting the ratio.

[0017] According to the above, the color consistency of LED-based lighting devices is improved by correcting the color ratio based on the aging of the LEDs.

[0018] In one example, the controller includes:

[0019] - a first color metric for indicating degradation of said at least one LED in said first LED channel over time;

[0020] - a second color metric for indicating degradation of said at least one LED in said second channel over time,

[0021] Wherein the controller is arranged to correct the color ratio based on the first colorimetric and the second colorimetric.

[0022] The above examples cover methods in which, for example, a controller corrects a color ratio based on a first color metric and a second color metric, wherein the metrics indicate degradation of the corresponding at least one LED over time. The time is not necessarily related to the time the LED actually emits light (i.e., the operating time or burn time of the LED).

[0023] A rough estimate of LED degradation can be based on the time that has elapsed, regardless of the number of burn hours of the LED in that particular elapsed time.

[0024] In another example, the first color metric and the second color metric indicate degradation of the corresponding at least one LED in the corresponding LED channel over time, wherein the time represents a time during which the corresponding LED channel is activated,

[0025] wherein the controller is arranged to:

[0026] Keep track of an amount of time that the first LED channel is activated and an amount of time that the second LED channel is activated, and correct the color ratio based on the first color metric, the second color metric, the tracked amount of time that the first LED channel has been activated, and the tracked amount of time that the second LED channel has been activated.

[0027] The concept involved in the above example is to track the actual burning hours of the LED, that is, the operating hours, to more accurately estimate the degradation of the LED. It is found that the degradation of the LED is mainly caused by the operating hours of the LED itself.

[0028] In this case, the controller can therefore keep track of the amount of time each of the LED channels is activated to obtain a measure of the operating time of each of the LED channels. The color ratio can then be corrected based on the operating time of each of the LED channels.

[0029] In another example,

[0030] - the first LED channel comprising the at least one LED is arranged to: emit light having a color temperature between 2000K-3000K;

[0031] - the second LED channel comprising the at least one LED is arranged to emit light having a color temperature between 6000K-7000K.

[0032] The above examples relate to an LED based lighting device arranged to emit white light. Note that the color temperature expressed in Kelvin scale K is the color appearance of the light produced by the LED based lighting device.

[0033] It is to be understood that, for example, a first LED channel is arranged to emit light having a color temperature of ˜2500 K, and a second LED channel may be arranged to emit light having a color temperature of ˜6500 K. By having an appropriate color ratio for the first LED channel and the second LED channel, any composite colored light between ˜2500 K and ˜6500 K may be obtained. If the ratio indicates that the first LED channel is more dominant than the second LED channel, the temperature of the composite colored light may be shifted toward ˜2500 K. If the ratio indicates that the second LED channel is more dominant than the first LED channel, the temperature of the composite colored light may be shifted toward ˜6500 K.

[0034] In a further example, each of the LED channels comprises a switch for activating the corresponding LED channel, and wherein the controller is arranged for controlling each of the switches in the LED channels based on the color ratio.

[0035] For example, the switch may be a transistor, a field effect transistor FET, a relay or anything similar.

[0036] In yet another example, the controller is arranged to control each of the switches using a pulse width modulated PWM signal.

[0037] In a second aspect, there is provided a method of operating an LED-based lighting device according to the first aspect, wherein the method comprises the following steps:

[0038] - activating, by the controller, the first LED channel and the second LED channel based on the color ratio, so that the LED-based lighting device emits light having a specific color;

[0039] - correcting, by the controller, the color ratio based on aging of the at least one LED in the first LED channel and aging of the at least one LED in the second LED channel, thereby ensuring color consistency of the LED-based lighting device over time.

[0040] It is noted that the advantages and limitations disclosed in relation to the embodiments of the first aspect of the invention also correspond to the embodiments of the second aspect of the invention, ie the method of operating a retrofitted light emitting diode LED based lighting device.

[0041] In one example, the controller includes a first color metric for indicating degradation of the at least one LED in the first LED channel over time and a second color metric for indicating degradation of the at least one LED in the second channel over time, wherein the correcting step includes:

[0042] - correcting, by the controller, the color ratio based on the first colorimetric and the second colorimetric.

[0043] In a further example, the first color metric and the second color metric indicate degradation of the corresponding at least one LED in the corresponding LED channel over time, wherein the time represents a time during which the corresponding LED channel is activated, wherein the method further comprises the steps of:

[0044] keeping track, by the controller, of an amount of time that the first LED channel is activated and an amount of time that the second LED channel is activated, and

[0045] The color ratio is corrected, by the controller, based on the first color metric, the second color metric, the tracked amount of time that the first LED channel has been activated, and the tracked amount of time that the second LED channel has been activated.

[0046] In another example:

[0047] - the first LED channel comprising the at least one LED is arranged to: emit light having a color temperature between 2000K-3000K;

[0048] - the second LED channel comprising the at least one LED is arranged to emit light having a color temperature between 6000K-7000K.

[0049] In a further example, each of the LED channels comprises a switch for activating the corresponding LED channel, and wherein the correcting step comprises:

[0050] Each of the switches in the LED channel is controlled by the controller based on the color ratio.

[0051] In yet another example, the controlling step includes:

[0052] Each of the switches is controlled by the controller using a pulse width modulation (PWM) signal.

[0053] In further examples, the aging of the at least one LED is based on any of:

[0054] - degradation of the lumen output of the at least one LED over time, and / or

[0055] - A color shift of the at least one LED over time.

[0056] The inventors have found that LEDs may also exhibit color shift over time. This is caused, for example, by silver mirror discoloration and phosphor deterioration. This may also be caused by deterioration of the encapsulation material.

[0057] In a third aspect, a computer program product is provided, comprising a computer-readable medium having instructions stored thereon, which, when executed by a controller of a light emitting diode (LED) based lighting device, causes the LED based lighting device to implement a method according to any of the examples provided above.

[0058] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 shows a portion of an LED-based lighting device according to the present disclosure;

[0060] Figure 2 A typical example of LED degradation over time for two different LEDs is shown;

[0061] Figure 3 A flow chart of a method according to the present disclosure is shown. DETAILED DESCRIPTION

[0062] Figure 1 A portion 1 of an LED based lighting device according to the present disclosure is shown. More specifically, a current splitter is shown for splitting the LED current between a plurality of channels.

[0063] The LED current splitter may be included in a multi-channel light emitting diode (LED) based lighting device. Multi-channel indicates that the LED based lighting device has multiple channels, where each channel is related to an LED emitting a specific color. For example, the first channel may be related to emitting red light, the second channel may be related to emitting green light, and the third channel may be related to emitting blue light.

[0064] In a typical example, a first channel may involve emitting warm white light, a second channel may involve emitting cool white light, and a third channel may involve emitting another white light.

[0065] Figure 1 The LED current splitter has three channels as indicated by reference numerals 3, 4 and 5, respectively. Each channel includes a switch 6, 7, 8 and a corresponding at least one LED 9, 10, 11. Each of the switches 6, 7, 8 can be controlled by a controller using a pulse width modulation PWM signal. The above allows the controller to emit three different primary colors, such as red, green and blue, and allows the controller to emit multiple secondary colors by mixing the channels with each other using specific color ratios.

[0066] Thus, the color ratio may define the amount of time each of the switches is activated relative to each other. Thus, the color ratio may mix the colors emitted by each of the channels.

[0067] A current source 2 is indicated for providing the LED current to the LED current splitter. Note that the current source 2 can be implemented in a variety of ways. For example, the current source 2 can be implemented as an LED driver.

[0068] The inventors have noticed that the LEDs in the first channel 3 may have different aging properties compared to the LEDs in the second channel 4 and the LEDs in the third channel 5. The LEDs in the second channel 4 may also have different aging properties compared to the LEDs in the third channel 5.

[0069] For example, aging may relate to the amount of lumens emitted by a corresponding LED over time. Due to aging factors, the amount of lumens may decrease over time.

[0070] Another possibility is the occurrence of color shift over time. According to the present disclosure, this is also covered by the aging process.

[0071] A controller may be provided which is then arranged to correct the color ratio based on aging of the at least one LED in the first LED channel and aging of the at least one LED in the second LED channel, thereby ensuring color consistency of the specific color of the LED-based lighting device over time.

[0072] Figure 1An example is shown in which three LED strings are used. An LED current splitter with two LED strings may also be used. In this example, the first channel may be directed to emitting warm white light, and the second channel may be directed to emitting cool white light.

[0073] For example, to emit a particular color of light, the switch indicated by reference numeral 6 may have a 50% duty cycle, and the switch indicated by reference numeral 7 may also have a 50% duty cycle. In other words, the color ratio is 1:1 because each of the switches is activated for the same amount of time. Due to the different properties of the LEDs with reference numerals 6 and 7, and considering the consistency of color, the color ratio can be adjusted over time to ensure color consistency. For example, the ratio can be modified to 1:1, 02 or any similar value.

[0074] The aging properties of each of the LEDs can be stored in the LED-based lighting device itself, such as in a memory coupled to the controller. The controller can keep track of the number of burn hours for each of the LEDs and can calculate the color ratio in an ongoing process.

[0075] Figure 2 Typical examples of LED degradation over time are shown for two different LEDs.

[0076] Here, the vertical axis 23 represents the amount of lumens, expressed as a percentage compared to the initial amount of lumens emitted by the corresponding LED. The horizontal axis 24 represents the actual burning hours of the corresponding LED.

[0077] It is shown that a first LED (eg, as indicated with reference numeral 21 ) degrades differently over time compared to a second LED (eg, as indicated with reference numeral 22 ).

[0078] Figure 3 A flow chart of a method according to the present disclosure is shown.

[0079] Method 31 involves operating an LED-based lighting device as described above, wherein the method comprises the following steps:

[0080] - activating 32, by the controller based on the color ratio, the first LED channel and the second LED channel so that the LED-based lighting device emits light having a specific color;

[0081] - correcting 33, by the controller, the color ratio based on aging of the at least one LED in the first LED channel and aging of the at least one LED in the second LED channel, thereby ensuring color consistency of the LED-based lighting device over time.

[0082] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other changes to the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit can implement the functions of several items recorded in the claims. The fact that certain measures are recorded in mutually different dependent claims does not indicate that the combination of these measures cannot be used advantageously. The computer program can be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium supplied with or as part of other hardware, but the computer program can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any figure mark in the claims should not be interpreted as limiting its scope.

Claims

1. A light emitting diode (LED) based lighting device arranged to emit colored light, wherein the LED based lighting device comprises: - a first LED channel comprising at least one LED arranged to emit light of a first color and comprising a switch (6); a second LED channel comprising at least one LED arranged to emit light of a second color different from the first color, and comprising a further switch (7); - a memory for storing an aging property of each of the LEDs; - a controller arranged to: - activating the first LED channel and the second LED channel by controlling the switch (6) and the further switch (7) with a pulse width signal based on a color ratio so that the LED-based lighting device emits light having a specific color; as well as -Keeping track of the amount of time the first LED channel is activated and the amount of time the second LED channel is activated, and correcting the color ratio based on the aging properties of each of the LEDs and the tracked amount of time the first LED channel has been activated and the tracked amount of time the second LED channel has been activated, thereby ensuring color consistency of the particular color of the LED-based lighting device over time.

2. The LED-based lighting device of claim 1, wherein: - the first LED channel comprising the at least one LED is arranged to: emit light having a color temperature between 2000K-3000K; - the second LED channel comprising the at least one LED is arranged to emit light having a color temperature between 6000K-7000K.

3. The LED-based lighting device of claim 1, wherein the LED-based lighting device further comprises a third LED channel, the third LED channel comprising at least one LED, wherein: the first LED channel is arranged to emit red light, the second LED channel is arranged to emit green light, and the third LED channel is arranged to emit blue light, or The first LED channel is arranged to emit warm white light, the second LED channel is arranged to emit cool white light, and the third LED channel is arranged to emit another white light.

4. The LED-based lighting device according to claim 1, wherein the controller is arranged for controlling the switch (6) and each of the further switches (7) using a pulse width modulated (PWM) signal.

5. The LED-based lighting device of any one of claims 1-4, wherein the aging of the at least one LED is based on any of the following: - degradation of the lumen output of the at least one LED over time, and / or - A color shift of the at least one LED over time.

6. A method of operating an LED-based lighting device according to any one of claims 1 to 5, wherein the method comprises the following steps: - activating, by the controller, the first LED channel and the second LED channel based on the color ratio, so that the LED-based lighting device emits light having a specific color; - storing an aging property of each of the LEDs in a memory; - keeping track of the amount of time the first LED channel is activated and the amount of time the second LED channel is activated; -The controller corrects the color ratio based on aging properties of each of the LEDs and the tracked amount of time that the first LED channel has been activated and the tracked amount of time that the second LED channel has been activated, thereby ensuring color consistency of the particular color of the LED-based lighting device over time.

7. The method of operating an LED-based lighting device of claim 6, wherein the controller includes a first color metric for indicating degradation of the at least one LED in the first LED channel over time and a second color metric for indicating degradation of the at least one LED in the second LED channel over time, wherein the step of correcting includes: - correcting, by the controller, the color ratio based on the first colorimetric and the second colorimetric.

8. The method of operating an LED-based lighting device of claim 7, wherein the first color metric and the second color metric indicate degradation of the corresponding at least one LED in the corresponding LED channel over time, wherein the time represents a time during which the corresponding LED channel is activated, and wherein the method further comprises the steps of: keeping track, by the controller, of an amount of time that the first LED channel is activated and an amount of time that the second LED channel is activated, and The color ratio is corrected, by the controller, based on the first color metric, the second color metric, the tracked amount of time that the first LED channel has been activated, and the tracked amount of time that the second LED channel has been activated.

9. A method of operating an LED-based lighting device according to any one of claims 6 to 8, wherein: - the first LED channel comprising the at least one LED is arranged to: emit light having a color temperature between 2000K-3000K; - the second LED channel comprising the at least one LED is arranged to emit light having a color temperature between 6000K-7000K.

10. The method of operating an LED-based lighting device according to any one of claims 6-8, wherein the LED-based lighting device further comprises a third LED channel, the third LED channel comprising at least one LED, wherein: the first LED channel is arranged to emit red light, the second LED channel is arranged to emit green light, and the third LED channel is arranged to emit blue light, or The first LED channel is arranged to emit warm white light, the second LED channel is arranged to emit cool white light, and the third LED channel is arranged to emit another white light.

11. A method of operating an LED-based lighting device according to any one of claims 6 to 8, wherein the step of activating comprises: The switch (6) and each of the further switches (7) are controlled by the controller using a pulse width modulated PWM signal.

12. A computer program product comprising a computer readable medium having stored thereon instructions, which when executed by a controller of a light emitting diode (LED) based lighting device causes the LED based lighting device to perform the method according to any one of claims 6-11.

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