A light-emitting diode (LED)-based lighting device configured to emit colored light, and a corresponding method for operating such an LED-based lighting device

Abstract

The present invention provides a light-emitting diode (LED)-based lighting device configured to emit colored light, the LED-based lighting device comprising: a first LED channel including at least one LED configured to emit light at a first color; a second LED channel including at least one LED configured to emit light at a second color different from the first color; and a controller configured to operate 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 particular color, wherein the controller is further configured to correct the color ratio based on aging of the at least one LED in the first LED channel and the at least one LED in the second LED channel, thereby ensuring color consistency of the particular 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 has at least two LED channels, and each LED channel is configured to emit light of a specific color.

Background Art

[0002] For various lighting applications, lighting devices utilizing light-emitting diodes (LEDs) have been developed. LED lamps, due to their long lifespan and high energy efficiency, are today designed for replacement of conventional fluorescent lamps, i.e., for retrofit applications. In such cases, retrofit LED lamps are generally adapted to fit the sockets of the respective lamp fixtures to be retrofitted. Further, since lamp maintenance is generally performed by the user, retrofit LED lamps should ideally be easily operable with any type of suitable fixture without the need to rewire the fixture.

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

[0004] More specifically, the present disclosure may be particularly applicable to an LED-based lighting device having two LED channels, wherein the first LED channel is for warm white emission and the second LED channel is for cool white emission.

[0005] Often, such LED-based lighting devices are provided with a current source, and the LED-based lighting device has a current divider for splitting the current across different channels.

[0006] More specifically, generally, there is an available controller having a plurality of LED channels, each channel being disposed with a switch, and thus each of the switches is configured to enable a specific corresponding channel. For example, the first switch can enable the red channel, the second switch can enable the green channel, the third switch can enable the blue channel, and so on.

[0007] The switch may be supplied with a pulse width modulation (PWM) signal having a specific duty cycle. The frequency of the PWM signal should be selected to exceed the refresh rate of the human eye. This prevents the user from seeing any flicker. By controlling the duty cycle, the contribution of each of the channels to the total amount of light emitted can be controlled, and thus the color of the light emitted by the LED-based lighting device can also be controlled.

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

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

MEANS FOR SOLVING THE PROBLEM

[0009] In a first aspect, an LED-based lighting device configured to emit colored light, - a first LED channel including at least one LED configured to emit light in a first color, - A second LED channel including at least one LED configured to emit light in a second color different from the first color; - An LED-based lighting device having a controller configured to operate 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.

[0010] The controller is further configured to correct the color ratio based on the aging deterioration of the at least one LED in the first LED channel and the at least one LED in the second LED channel, thereby ensuring the color consistency over time of the specific color of the LED-based lighting device.

[0011] The inventor's insight was that different types of LEDs may deteriorate differently over time. For example, warm white LEDs may deteriorate faster over time than cool white LEDs, or vice versa. The above can affect not only the intensity of the light emitted by the LED-based lighting device, but also the color of the LED-based lighting device. This disclosure is directed to the latter.

[0012] This can be explained as follows. Generally, the controller may use a certain setpoint for light of a specific color. Such a setpoint determines the ratio between different said LED channels. For example, the first LED channel may be active 60% of the period, and the second LED channel may be active 75% of the period. The combination of both LED channels results in the emission of a specific light. The inventor has found that the LEDs in the first channel may deteriorate over time differently than the LEDs in the second channel. Therefore, the ratio, i.e., the 60% to 75% ratio, should also be corrected based on the effect of that specific deterioration.

[0013] According to the present disclosure, the above is summarized as the aging degradation of the LED. Therefore, the aging degradation of the LED may cause a decrease in the emitted light or even a deviation in the color of the emitted light. When correcting the ratio, both of these can be taken into account.

[0014] Therefore, from the above, by correcting the color ratio based on the aging degradation of the LED, the color consistency of the LED-based lighting device is enhanced.

[0015] In an example, the controller - a first color measurement for indicating the aging degradation over time of the at least one LED in the first LED channel, and - a second color measurement for indicating the aging degradation over time of the at least one LED in the second LED channel, and the controller is configured to correct the color ratio based on the first color measurement and the second color measurement.

[0016] The above example covers, for example, a method in which the controller corrects the color ratio based on the first color measurement and the second color measurement, and these measurements indicate the aging degradation over time of the corresponding at least one LED. The period is not necessarily related to the period during which the LED is actually emitting light, i.e., the operating period or burning time of the LED.

[0017] A rough estimate of the degradation of the LED may be based on the elapsed time, regardless of the amount of the lighting time of the LED at a specific elapsed time.

[0018] In another example, the first color measurement and the second color measurement indicate the aging degradation over time of the corresponding at least one LED in the corresponding LED channel, the period represents the period during which the corresponding LED channel is operated, the controller Record the periods during which the first LED channel and the second LED channel are activated, and correct the color ratio based on the measurement of the first color, the measurement of the second color, the recorded period during which the first LED channel was activated, and the recorded period during which the second LED channel was activated.

[0019] The above example is directed to the concept that the actual lighting time of the LED, i.e., the operating time, is recorded in order to more accurately estimate the degradation of the LED. It has been found that the degradation of the LED is mainly due to the amount of operating time of the LED itself.

[0020] Therefore, in such a situation, the controller may record the period during which each of the LED channels is activated in order to obtain the magnitude of the operating period of each of the LED channels. In that case, the color ratio may be corrected based on the operating period of each of the LED channels.

[0021] In another example, - The first LED channel including the at least one LED is configured to emit light having a color temperature between 2000K and 3000K, - The second LED channel including the at least one LED is configured to emit light having a color temperature between 6000K and 7000K.

[0022] The above example is directed to an LED-based lighting device configured to emit white light. Note that the color temperature, represented in Kelvin scale, K, is the appearance of the color of the light generated by the LED-based lighting device.

[0023] For example, it should be understood that the first LED channel may be configured to emit light having a color temperature of ~2500K, and the second LED channel may be configured to emit light having a color temperature of ~6500K. By adjusting the color ratio for the first LED channel and the second LED channel, any mixed colored light between ~2500K and ~6500K can be obtained. When the ratio indicates that the first LED channel is dominant over the second LED channel, the temperature of the mixed colored light may shift towards ~2500K. When the ratio indicates that the second LED channel is dominant over the first LED channel, the temperature of the mixed colored light may shift towards ~6500K.

[0024] In a further example, each of the LED channels has a switch for operating the corresponding LED channel, and the controller is configured to control each of the switches within the LED channels based on the color ratio.

[0025] The switch may be, for example, a transistor, a field effect transistor (FET), a relay, or the like.

[0026] In yet another example, the controller is configured to control each of the switches using a pulse width modulation (PWM) signal.

[0027] In a second aspect, a method of operating an LED-based lighting device according to any one of claims 1 to 5, - operating the first LED channel and the second LED channel by the controller based on the color ratio such that the LED-based lighting device emits light having a specific color; - A step of correcting the color ratio based on the aging degradation of the at least one LED in the first LED channel and the aging degradation of the at least one LED in the second LED channel by the controller, thereby ensuring the color consistency of the LED-based lighting device over time, is provided in a method of operating an LED-based lighting device.

[0028] It should be noted that the advantages and definitions disclosed for embodiments of the first aspect of the present invention also correspond to embodiments of the second aspect of the present invention, which is a method of operating a retrofit light-emitting diode (LED)-based lighting device.

[0029] In an example, the controller includes a first color measurement for indicating the aging degradation of the at least one LED in the first LED channel and a second color measurement for indicating the aging degradation of the at least one LED in the second LED channel, and the step of correcting includes - A step of correcting the color ratio by the controller based on the first color measurement and the second color measurement.

[0030] In a further example, the first color measurement and the second color measurement indicate the aging degradation of the corresponding at least one LED in the corresponding LED channel, the period represents the period during which the corresponding LED channel is operated, and the method further includes A step of recording, by the controller, the periods during which the first LED channel and the second LED channel are operated; and A step of correcting the color ratio by the controller based on the first color measurement, the second color measurement, the recorded period during which the first LED channel was operated, and the recorded period during which the second LED channel was operated.

[0031] In another example, - The first LED channel including the at least one LED is configured to emit light having a color temperature between 2000K and 3000K. - The second LED channel including the at least one LED is configured to emit light having a color temperature between 6000K and 7000K.

[0032] In a further example, each of the LED channels has a switch for operating the corresponding LED channel, and the correcting step comprises: controlling, by the controller, each of the switches in the LED channels based on the color ratio.

[0033] In yet another example, the controlling step comprises: controlling, by the controller, each of the switches using a pulse width modulation (PWM) signal.

[0034] In a further example, the aging degradation of the at least one LED is - the degradation of the lumen output of the at least one LED over time and / or - based on any of the color shifts of the at least one LED over time.

[0035] The inventor has found that the LEDs may exhibit color shift over time. This is caused, for example, by the discoloration of a silver mirror and the denaturation of a phosphor. This may also be caused by the denaturation of the package material.

[0036] In a third aspect, there is provided a computer program product including a computer-readable medium having instructions stored thereon which, when executed by a controller of a light-emitting diode (LED)-based lighting device, cause the LED-based lighting device to perform a method according to any of the examples provided above.

[0037] These and other aspects of the invention will be described and clarified with reference to the embodiments below.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0039] FIG. 1 shows a part 1 of an LED-based lighting device according to the present disclosure. More specifically, a current divider for splitting the LED current among a plurality of channels is shown.

[0040] The LED current divider can be included in a multi-channel light-emitting diode (LED)-based lighting device. The multi-channel indicates that the LED-based lighting device has a plurality of channels, and each channel is for an LED that emits a specific color. For example, the first channel may be for red emission, the second channel may be for green emission, and the third channel may be for blue emission.

[0041] In a general example, the first channel may be for warm white emission, the second channel may be for cool white emission, and the third channel may be for further white emission.

[0042] The LED current divider of FIG. 1 has three channels, as indicated by reference numerals 3, 4, and 5, respectively. Each channel has switches 6, 7, 8 and at least one LED 9, 10, 11, respectively. Each of the switches 6, 7, 8 can be controlled by a controller with a pulse width modulation (PWM) signal. The above enables the controller to emit a plurality of secondary colors by emitting three different primary colors, for example, red, green, and blue, and mixing the channels with each other using a specific color ratio.

[0043] Accordingly, the color ratio may define the period for which each of the switches is operated relative to each other. Accordingly, the color ratio can mix the colors emitted by each of the channels.

[0044] A current source 2 for supplying an LED current to the LED current divider is shown. Note that the current source 2 can be implemented in various ways. For example, the current source 2 may be implemented as an LED driver.

[0045] The inventor notes that the LEDs in the first channel 3 may have different aging degradation characteristics 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 degradation characteristics compared to the LEDs in the third channel 5.

[0046] Aging degradation can be directed, for example, to the lumen amount emitted by each LED over time. The lumen amount can decrease over time due to aging degradation factors.

[0047] Another possibility is that color shift occurs over time. According to the present disclosure, this is also included in the aging degradation process.

[0048] In that case, a controller may be provided that is configured to correct the color ratio based on the aging degradation of the at least one LED in the first LED channel and the at least one LED in the second LED channel, thereby ensuring color consistency over time of the specific color of the LED-based lighting device.

[0049] FIG. 1 shows an example where three LED strings are used. An LED current divider with two LED strings can also be used. In this example, the first channel may be for warm white light emission, and the second channel may be for cool white light emission.

[0050] For example, in order to emit light of a specific color, a switch as indicated by reference numeral 6 may have a duty cycle of 50%, and a switch as indicated by reference numeral 7 may also have a duty cycle of 50%. In other words, since each of the switches is operated for the same period of time, the color ratio is 1:1. Due to the different characteristics of the LEDs with reference numerals 6 and 7, and for the sake of color consistency, the color ratio can be adapted over time to ensure color consistency. This ratio can be corrected, for example, to 1:1.02 or the like.

[0051] The aging degradation characteristics of each LED may be stored in the LED-based lighting device itself, for example, in a memory coupled to the controller. The controller may record the amount of on-time of each LED and calculate the color ratio in the ongoing process.

[0052] FIG. 2 shows a general example of the aging degradation of two different LEDs over time.

[0053] Here, the vertical axis 23 shows the lumen amount as a percentage compared to the initial lumen amount emitted by each LED. The horizontal axis 24 shows the actual on-time of each LED.

[0054] The first LED, such as that indicated by reference numeral 21, has been shown to degrade over time in a manner different from that of the second LED, such as that indicated by reference numeral 22.

[0055] FIG. 3 shows a flowchart 31 of a method according to the present disclosure.

[0056] Method 31 is directed to operating an LED-based lighting device according to any one of claims 1 to 5, the method comprising: - Step 32 of operating the first LED channel and the second LED channel by the controller based on the color ratio such that the LED-based lighting device emits light having a specific color; - Step 33 of correcting the color ratio by the controller based on the aging degradation of the at least one LED in the first LED channel and the aging degradation of the at least one LED in the second LED channel, thereby ensuring color consistency of the LED-based lighting device over time.

[0057] A person skilled in the art can understand and achieve other modifications to the disclosed embodiments from the study of the drawings, the description, and the appended claims when implementing the invention described in the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the singular form does not exclude a plurality. A single processor or other unit may perform the functions of a plurality of items recited in the claims. Merely the fact that certain means are recited in mutually different dependent claims does not indicate that these means cannot be used advantageously in combination. A computer program may be stored / distributed on a suitable medium such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but may also be distributed in other forms via the Internet or other wired or wireless telecommunications systems. Any reference signs in the claims should not be construed as limiting the claims.

Claims

1. An LED-based lighting device configured to emit colored light, comprising: a first LED channel including at least one LED configured to emit light in a first color and a switch; a second LED channel including at least one LED configured to emit light in a second color different from the first color and a further switch; a memory for storing the aging degradation characteristics of each of the LEDs; a controller, wherein the first LED channel and the second LED channel are operated by controlling the switch and the further switch with a pulse width signal based on a color ratio such that the LED-based lighting device emits light having a specific color; recording the periods during which the first LED channel and the second LED channel are operated, and correcting the color ratio based on each of the aging degradation characteristics of the LEDs, the recorded period during which the first LED channel is operated, and the recorded period during which the second LED channel is operated, thereby ensuring color consistency over time of the specific color of the LED-based lighting device; and a controller configured as such. The LED-based lighting device, wherein the aging degradation of the at least one LED is based on a color shift of the at least one LED over time.

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

3. The LED-based lighting device according to claim 1 or 2, wherein each of the LED channels has a switch for operating the corresponding LED channel, and the controller is configured to control each of the switches within the LED channels based on the color ratio.

4. The LED-based lighting device according to claim 3, wherein the controller is configured to control each of the switches using a pulse width modulation signal.

5. The LED-based lighting device according to any one of claims 1 to 4, wherein the aging deterioration of the at least one LED is further based on the deterioration of the lumen amount 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, comprising: operating, by the controller, the first LED channel and the second LED channel based on the color ratio such that the LED-based lighting device emits light having a specific color; storing, in a memory, the aging deterioration characteristics of each of the LEDs; recording the periods during which the first LED channel and the second LED channel are operated; correcting, by the controller, the color ratio based on the aging deterioration characteristics of each of the LEDs, the recorded period during which the first LED channel was operated, and the recorded period during which the second LED channel was operated, thereby ensuring color consistency over time of the specific color of the LED-based lighting device.

7. The controller includes a first color measurement for indicating the aging deterioration over time of the at least one LED in the first LED channel and a second color measurement for indicating the aging deterioration over time of the at least one LED in the second LED channel, and the correcting step includes: correcting, by the controller, the color ratio based on the first color measurement and the second color measurement. A method of operating an LED-based lighting device according to claim 6.

8. The first color measurement and the second color measurement indicate the aging deterioration over time of the corresponding at least one LED in the corresponding LED channel, the period represents the period during which the corresponding LED channel is operated, and the method includes: recording, by the controller, the periods during which the first LED channel and the second LED channel are operated; A method of operating an LED-based lighting device according to claim 7, further comprising the step of correcting the color ratio by the controller based on the measurement of the first color, the measurement of the second color, the recorded period during which the first LED channel was activated, and the recorded period during which the second LED channel was activated.

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

10. Each of the LED channels has a switch for activating the corresponding LED channel, and the correcting step comprises A method of operating an LED-based lighting device according to any one of claims 6 to 9, wherein the controller controls each of the switches in the LED channel based on the color ratio.

11. The controlling step comprises A method of operating an LED-based lighting device according to claim 10, wherein the controller controls each of the switches using a pulse width modulation signal.

12. A computer-readable medium comprising instructions stored on the computer-readable medium for causing a controller of an LED-based lighting device to perform the method according to any one of claims 6 to 11 when executed by the controller of the LED-based lighting device.

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