Illumination devices and related systems and methods

• US 8,773,336 B2
• Filed: 08/05/2010
• Issued: 07/08/2014
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Ketra, Inc. (Lutron Electronics)
• Inventors: Knapp, David J.
• Primary Examiner(s): Pappas, Claire X
• Assistant Examiner(s): PHAM LU, NGAN T
• Application Number:
  US12/806,118
• Publication Number:
  US 20110069094A1
• Time in Patent Office: 1,433 Days
• Field of Search: None
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: H04L 12/40013 Details regarding a bus controller
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback

Abstract

Illumination devices and related systems and methods are closed that can be used for LCD (Liquid Crystal Display) backlights, LED lamps, or other applications. The illumination devices can include a photo detector, such as a photodiode or an LED or other light detecting device, and one or more LEDs of different colors. A related method can be implemented using these illumination devices to maintain precise color produced by the blended emissions from such LEDs. One application for the illumination devices is backlighting for FSC (Field Sequential Color) LCDs (Liquid Crystal Displays). FSC LCDs temporally mix the colors in an image by sequentially loading the red, green, and blue pixel data of an image in the panel and flashing the different colors of an RGB backlight. Precise and uniform color temperature across such a display can be advantageously maintained by continually monitoring ratios of photodiode currents induced by the different colored LEDs in each illumination device as each color is flashed.

Claims

1. A device, comprising:

at least a first LED and a second LED, wherein the first and second LEDs are configured to emit different wavelength light from each other;

a controller configured to drive the first LED to emit light during a first time period when the second LED does not emit light, and to drive the second LED to emit light during a second time period when the first LED does not emit light; and

a light detector configured to detect an intensity of light produced by the first LED during the first time period and to detect an intensity of light produced by the second LED during the second time period;

wherein the controller is further configured to use the light detector to measure a temperature of the device by;

supplying two different currents to the light detector during a third time period when the first and second LEDs are not emitting light; and

measuring a difference between voltages developed across the light detector when supplied with the two different currents, wherein the difference in the voltages is proportion to the temperature; and

wherein the controller is further configured to use a ratio of signals induced in the light detector by the first and second LEDs during the first and second time periods and the temperature measured during the third time period to adjust the intensity of light produced by at least one of the LEDs.

2. The device as recited in claim 1, wherein the controller is configured to compare a ratio of currents induced in the light detector by the first and second LEDs to a desired ratio of currents to determine if the intensity of light produced by at least one of the LEDs should be adjusted.

3. The device as recited in claim 2, wherein the controller is further configured to adjust a drive current supplied to the at least one of the LEDs based upon the comparison.

4. The device as recited in claim 2, further comprising at least three LEDs, wherein the LEDs comprise at least one red LED, at least one green LED and at least one blue LED.

5. The device as recited in claim 1, wherein the LEDs are configured to provide a light source for an LED lamp.

6. The device as recited in claim 1, wherein the LEDs are configured to provide a light source for a projector.

7. The device as recited in claim 1, wherein the LEDs are configured to provide a light source for a digital billboard.

8. The device as recited in claim 1, wherein the LEDs comprise organic LEDs.

9. The device as recited in claim 8, wherein the LEDs are configured to provide a light source for a active matrix organic LED display.

10. The device as recited in claim 1, wherein the LEDs are configured to provide a backlight for a liquid crystal display (LCD).

11. The device as recited in claim 1, wherein the LEDs are configured to provide a backlight for a LCD configured to mix color temporally.

12. The device as recited in claim 1, wherein the LEDs are configured to provide a backlight for a LCD configured to sequence colors in fields of red, green, and blue image data.

13. The device as recited in claim 1, wherein the LEDs are configured to provide a backlight for a LCD not having a color filter.

14. The device as recited in claim 1, wherein the light detector is comprised of a silicon photodiode.

15. The device as recited in claim 14, wherein the silicon photodiode is part of an integrated circuit comprising the controller.

16. The device as recited in claim 15, wherein the silicon photodiode comprises a diffused junction between a P-type substrate and an N-type diffusion layer.

17. The device as recited in claim 15, wherein the silicon photodiode comprises a diffused junction between an N-type substrate and a P-type diffusion later.

18. The device as recited in claim 15, wherein the controller is configured to produce drive current for the first and second LEDs.

19. The device as recited in claim 15, wherein the controller is configured to measure a current induced in the silicon photodiode.

20. The device as recited in claim 19, wherein the controller is further configured to measure a current induced in the silicon photodiode when the first and second LEDs are not emitting light.

21. The device as recited in claim 19, wherein the controller is further configured to measure a current induced in the silicon photodiode when the first and second LEDs are not emitting light and to determine a difference as compared to a current measured when only the first LED or the second LED is emitting light.

22. The device as recited in claim 15, wherein the controller is configured to produce drive current for the first and second LEDs and to measure a current induced in the silicon photodiode.

23. The device as recited in claim 14, wherein the silicon photodiode is connected to an integrated circuit comprising the controller through PCB traces or bond wires.

24. The device as recited in claim 14, wherein the controller is further configured to compare a ratio of current induced in the silicon photodiode by the first and second LEDs to a desired ratio of currents stored within the controller.

25. The device as recited in claim 24, wherein the controller makes a determination to adjust an intensity of light produced by an LED in part based on a difference between the ratio of induced currents and the desired ratio of currents.

26. The device as recited in claim 1, wherein the first and second LEDs are included within a package.

27. The device as recited in claim 26, wherein the package is further configured only to allow light to enter or leave the package from one surface of the package.

28. The device as recited in claim 1, further comprising a device package surrounding the first and second LEDs, and wherein cathodes of the first and second LEDs are connected together and to one pin of the package.

29. The device as recited in claim 1, further comprising a device package surrounding the first and second LEDs, and wherein anodes of the first and second LEDs are each connected to at least one pin of the package.

30. The device as recited in claim 1, wherein the light detector comprises an LED.

31. The device as recited in claim 30, wherein the light detecting LED is integrated on a same die with at least the first LED or the second LED.

32. A method for controlling color of light produced by at least two LEDs that emit light at different wavelengths, comprising:

emitting light from a first LED having a first wavelength;

emitting light from a second LED having a second wavelength different from the first wavelength;

generating a first signal from a detector responsive to light emitted by the first LED;

generating a second signal from a detector responsive to light emitted by the second LED;

determining a ratio of the first and second signals;

determining a temperature by measuring a difference between voltages developed across the detector when the detector is supplied with the two different currents, wherein the difference in the voltages is proportional to the temperature; and

adjusting an average drive current supplied to at least one of the first and second LEDs based in part on the ratio and the temperature.

33. The method as recited in claim 32, wherein the light detector and the first and second LEDs are included in a same package.

34. The method as recited in claim 33, further comprising emitting light with the first LED during a time when the second LED is not emitting light and emitting light with the second LED during a time when the first LED is not emitting light.

35. The method as recited in claim 34, further comprising comparing the ratio to a desired ratio prior to adjusting the average drive current and performing the adjusting step based upon a result of the comparing step.

36. A system for controlling color of light produced by at least two LEDs that emit light at different wavelengths, comprising:

a first LED and a second LED configured to emit light at different wavelengths;

a detector configured to receive light from the first LED and the second LED and to generate a first signal based upon the light emitted by the first LED and a second signal based upon the light emitted by the second LED; and

control circuitry configured to use the light detector to determinie a temperature by measuring a difference between voltages developed across the detector when the detector is supplied with the two different currents, wherein the difference in the voltages is proportional to the temperature, and wherein the controller is further configured to determine a ratio of the first and second signals and to adjust an average drive current to at least one of the LEDs based in part on the ratio and the temperature.

37. The system as recited in claim 36, wherein the light detector and the LEDs are included in a same package.

38. The system as recited in claim 37, wherein the first LED is configured to emit light during a time when the second LED is not emitting light and wherein the second LED is configured to emit light during a time when the first LED is not emitting light.

39. The system as recited in claim 38, wherein the control circuitry is further configured to compare the ratio to a desired ratio to determine an adjustment for the average drive current.

40. A controller to control light emitted from a device, comprising:

control circuitry configured to drive a first LED to emit light during a first time period when a second LED does not emit light, and to drive a second LED to emit light during a second time period when the first LED does not emit light;

measurement circuitry coupled to a light detector for detecting a first signal induced on the light detector by light from the first LED during the first time period, for detecting a second signal induced on the light detector by light from the second LED during the second time period, and for detecting a temperature of the light detector by measuring a difference between voltages developed across the detector when the detector is supplied with the two different currents, wherein the difference in the voltages is proportional to the temperature; and

wherein the control circuitry is further configured to compare a ratio of the first and second signals to a desired ratio and to adjust an intensity of light produced by at least one of the LEDs based on the comparison and the temperature.

41. The controller as recited in claim 40, wherein the ratio of the first and second signals and the temperature is used to determine an intensity of light produced by each LED.

42. The controller as recited in claim 40, further comprising the light detector coupled to the measurement circuitry.

43. The controller as recited in claim 42, wherein the light detector comprises a silicon photodiode.

44. The controller as recited in claim 43, wherein the silicon photodiode is also used to measure temperature.

45. The controller as recited in claim 44, wherein the control circuitry, the measurement circuitry and silicon photodiode are included in a same integrated circuit.

46. The controller of claim 42, wherein the light detector comprises an LED.

47. A device, comprising:

a first LED configured to emit light at a first wavelength;

a second LED configured to emit light at a second wavelength different from the first wavelength;

a light detector comprising a light detecting LED integrated on a same die with the first LED; and

a controller configured to determine a ratio of signals induced in the light detector by the first and second LEDs when the first and second LEDs are configured to emit light, and wherein the controller is further configured to determine a temperature of the device by supplying two different currents to the light detector when the first and second LEDs are not emitting light, and measuring a difference between voltages developed across the light detector when supplied with the two different currents, wherein the difference in the voltages is proportional to the temperature.

48. The device as recited in claim 47, wherein the controller is further configured to:

drive the first LED to emit light during a first time period when the second LED does not emit light;

drive the second LED to emit light during a second time period when the first LED does not emit light;

use the light detector to detect an intensity of light produced by the first LED during the first time period, and an intensity of light produced by the second LED during the second time period; and

use the light detector to determine the temperature of the device during a third time period when the first and second LEDs are not emitting light.

49. The device as recited in claim 48, wherein the LED is configured to reside in a backlight for a liquid crystal display (LCD).

50. The device as recited in claim 48, wherein the LED is configured to reside in a backlight for a LCD configured to mix color temporally.

51. The device as recited in claim 48, wherein the LED is configured to reside in a backlight for a LCD configured to sequence colors in fields of red, green, and blue image data.

52. The device as recited in claim 48, wherein the LED is configured to reside in a backlight for a LCD not having a color filter.

53. The device as recited in claim 47, wherein the controller is configured to use the ratio of signals induced in the light detector by the first and second LEDs to determine the intensity of light produced by each LED.

54. The device as recited in claim 53, further comprising at least three LEDs, wherein the LEDs comprise a least one red LED, at least one green LED and at least one blue LED.