A LIGHT EMITTING DIODE, LED, BASED LIGHTING DEVICE ARRANGED TO EMIT COLORED LIGHT AS WELL AS A CORRESPONDING METHOD FOR OPERATING SUCH A LED BASED LIGHTING DEVICE

Abstract

A Light Emitting Diode, LED, based lighting device arranged to emit colored light, wherein said LED based lighting device comprises a first LED channel comprising at least one LED arranged for emitting light at a first color, a second LED channel comprising at least one LED arranged for emitting light at a second color, said second color being different to said first color, a controller arranged for activating said first LED channel and said second LED channel based on a color ratio such that said LED based lighting device emits light having a particular color, wherein said controller is further arranged for correcting said color ratio based on aging of said at least one LED in said first LED channel and on said at least one LED in said second LED channel, thereby ensuring color consistency of said particular color of said LED based lighting device over time.

Claims

1. A Light Emitting Diode (LED) based lighting device arranged to emit colored light, wherein said LED based lighting device comprises: a first LED channel comprising at least one LED arranged for emitting light at a first color and a switch; a second LED channel comprising at least one LED arranged for emitting light at a second color, said second color being different to said first color and a further switch; a memory for storing aging properties of each of the LED's; and a controller arranged for: activating said first LED channel and said second LED channel by controlling the switch and the further switch with a pulse width signal based on a color ratio such that said LED based lighting device emits light having a particular color; and keeping track of amounts of time that said first LED channel and said second LED channel are activated, and correcting said color ratio based on the aging properties of each of the LEDs and said tracked amount of time that said first LED channel has been activated and said tracked amount of time that said second LED channel has been activated, thereby ensuring color consistency of said particular color of said LED based lighting device over time.

2. The LED based lighting device in accordance with claim 1, wherein: said first LED channel comprising said at least one LED is arranged for emitting light having a color temperature of between 2000K-3000K; and said second LED channel comprising said at least one LED is arranged for emitting light having a color temperature of between 6000K-7000K.

3. The LED based lighting device in accordance with claim 1, wherein each of said LED channels comprises a switch for activating said corresponding LED channel, and wherein said controller is arranged for controlling each of said switches in said LED channels based on said color ratio.

4. The LED based lighting device in accordance with claim 3, wherein said controller is arranged for controlling each of said switches using a Pulse Width Modulation, PWM, signal.

5. The LED based lighting device in accordance with claim 1, wherein said aging of said at least one LED is based on any of: deterioration of an amount of lumen of said at least one LED over time, and/or a color shift of said at least one LED over time.

6. A method of operating an LED based lighting device in accordance with any of the previous claims, wherein said method comprises the steps of: activating, by said controller, said first LED channel and said second LED channel based on said color ratio such that said LED based lighting device emits light having a particular color; storing, in a memory, aging properties of each of the LED's: keeping track of amounts of time that said first LED channel and said second LED channel are activated; and correcting, by said controller, said color ratio based on aging properties of each of the LEDs and said tracked amount of time that said first LED channel has been activated and said tracked amount of time that said second LED channel has been activated, thereby ensuring color consistency of said particular color of said LED based lighting device over time.

7. The method of operating an LED based lighting device in accordance with claim 6, wherein said controller comprises a first color measure for indicating a deterioration of said at least one LED in said first LED channel over time and a second color measure for indicating a deterioration of said at least one LED in said second channel over time, wherein said step of correcting comprises: correcting, by said controller, said color ratio based on said first color measure and said second color measure.

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

9. The method of operating an LED based lighting device in accordance with claim 6, wherein: said first LED channel comprising said at least one LED is arranged for emitting light having a color temperature of between 2000K-3000K; said second LED channel comprising said at least one LED is arranged for emitting light having a color temperature of between 6000K-7000K.

10. The method of operating an LED based lighting device in accordance with claim 8, wherein each of said LED channels comprises a switch for activating said corresponding LED channel, and wherein said step of correcting comprises: controlling, by said controller, each of said switches in said LED channels based on said color ratio.

11. The method of operating an LED based lighting device in accordance with claim 10, wherein said step of controlling comprises: controlling, by said controller, each of said switches using a Pulse Width Modulation, PWM, signal.

12. A computer program product comprising a non-transitory computer readable medium having instructions stored there on which, when executed by a controller of a Light Emitting Diode, LED, based lighting device, cause said LED based lighting device to carry out a method in accordance with claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 shows a part of an LED based lighting device in accordance with the present disclosure;

[0060] FIG. 2 shows a typical example of LED degradation over time for two different LED's;

[0061] FIG. 3 shows a flow chart of a method in accordance with the present disclosure.

DETAILED DESCRIPTION

[0062] FIG. 1 shows a part 1 of an LED based lighting device in accordance with the present disclosure. More specifically, a current splitter is shown for splitting an LED current between multiple channels.

[0063] The LED current splitter may be comprised in a multi-channel Light Emitting Diode, LED, based lighting device. Multi-channel indicates that the LED based lighting device has a plurality of channels, wherein each channel is directed to LED's emitting a particular color. For example, a first channel may be directed to emit red colored light, a second channel may be directed to emit green colored light and a third channel may be directed to emit blue colored light.

[0064] In a typical example, a first channel may be directed to emitting Warm White colored light, a second channel may be directed to emitting Cool White colored light, and a third channel may be directed to emitting a further White colored light.

[0065] The LED current splitter of FIG. 1 has three channels as indicated with reference numerals 3, 4 and 5, respectively. Each channel comprises a switch 6, 7, 8 and a respective at least one LED 9, 10, 11. Each of the switches 6, 7, 8 may be controlled with Pulse Width Modulation, PWM, signals by a controller. The above allows the controller to emit three different primary colors, for example red, green and blue, and to emit a plurality of secondary colors by mixing the channels with one another using a particular color ratio.

[0066] The color ratio may thus define the amount of time that each of the switches is activated with respect to one another. The color ratio may thus 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. It is noted that the current 2 source may be implemented in a variety of ways. For example, the current source 2 may be implemented as an LED driver.

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

[0069] Aging may, for example, be directed to the amount of Lumens emitted by the respective LED over time. The amount of lumens may decrease over time due to the aging factors.

[0070] Another possibility is that a color shift occurs over time. This is also encompassed, in accordance with the present disclosure, by the aging process.

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

[0072] FIG. 1 shows an example where three LED strings are used. An LED current splitter with two LED strings can also be used. In this example a first channel may be directed to emitting Warm White colored light and a second channel may be directed to emitting Cool White colored light.

[0073] For example, in order to emit a particular color light, the switch as indicated with reference numeral 6 may have a 50% duty cycle and the switch as indicated with reference numeral 7 may also have a 50% duty cycle. In other words, the color ratio is 1:1 as each of the switches is activated for the same amount of time. Due to the different properties of the LED's with reference numerals 6 and 7, and having the color consistency in mind, the color ratio may be adapted, over time, to ensure the color consistency. The ratio may, for example, be amended to 1:1.02 or anything alike.

[0074] The aging properties of each of the LED's may be stored in the LED based lighting device itself, for example in a memory coupled to the controller. The controller may keep track of the amount of burning hours of each of the LED's and may calculate the color ratio in an ongoing process.

[0075] FIG. 2 shows a typical example of LED degradation over time for two different LED's.

[0076] Here, the vertical axis 23 denoted the amount of Lumen, in percentage, compared to the initial amount of Lumen emitted by the respective LED. The horizontal axis 24 denoted the actual burning hours of the respective LED.

[0077] It is shown that a first LED, for example the one as indicated with reference numeral 21, degrades differently over time compared to the second LED, for example the one as indicated with reference numeral 22.

[0078] FIG. 3 shows a flow chart 31 of a method in accordance with the present disclosure.

[0079] The method 31 is directed to the operating an LED based lighting device in accordance with any of the previous claims, wherein said method comprises the steps of: [0080] activating 32, by said controller, said first LED channel and said second LED channel based on said color ratio such that said LED based lighting device emits light having a particular color; [0081] correcting 33, by said controller, said color ratio based on aging of said at least one LED in said first LED channel and on said at least one LED in said second LED channel, thereby ensuring color consistency of said LED based lighting device over time.

[0082] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims, 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 may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 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, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope thereof.