LED calibration systems and related methods

• US 8,471,496 B2
• Filed: 08/05/2010
• Issued: 06/25/2013
• 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): CRAWFORD, JASON
• Application Number:
  US12/806,121
• Publication Number:
  US 20110062874A1
• Time in Patent Office: 1,055 Days
• Field of Search: 315149-159, 315307-308, 315/311
• US Class Current: 315/307
• CPC Class Codes: H04L 12/43 with synchronous transmission, e.g. time division multiplex [TDM], slotted rings
• CPC Class Codes: H04L 12/437 Ring fault isolation or reconfiguration for SDH/SONET ring networks H04J3/085
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 2012/40273 the transportation system being a vehicle

Abstract

LED calibration systems and related methods are disclosed that use the photo-sensitivity of LEDs to correct for variations between LEDs during initial production and over the lifetime of systems using LEDs. The disclosed systems and methods include methods to set the color or color temperature produced by a group of LEDs during the manufacturing of a device such as a lamp, an LED display, or an LCD backlight, and maintaining such color or color temperature over the operating life of such a device. The methods involve measuring the intensity and/or wavelength of light produced by each LED within a group of LEDs and adjusting an amount of light generated by the LEDs to produce precise color and intensity from the group of LEDs. Two methods that operate some of the LEDs in photovoltaic or photoconductive mode to measure the light intensity produced by other LEDs in the group are presented. The first method uses an additional light source as a reference and determines the light intensity emitted from each LED relative to such reference, while the second method determines the light intensity emitted from each LED relative to each other.

Claims

1. A method for calibrating light produced by a group of LEDs comprising at least a first LED and a second LED, the method comprising:

configuring the first LED as a photo-detector to receive light emitted from the second LED and a light source during a first time;

measuring a ratio of photocurrents induced in the first LED by the second LED and the light source during the first time to determine an emission intensity for the second LED and the light source;

comparing the ratio of photocurrents to a ratio of photocurrents of known intensities to determine a change in emission intensity;

calibrating light produced by the group of LEDs by adjusting the emission intensity of the first LED, the second LED, the light source, or any combination thereof based upon the determined change in emission intensity.

2. The method as recited in claim 1, further comprising configuring the first LED as a light emitter to emit light along with other LEDs in the group during a second time.

3. The method as recited in claim 1, further comprising adjusting the emission intensity of the second LED and the light source based upon the determined change in emission intensity.

4. The method as recited in claim 1, further comprising determining a peak emission wavelength of the first LED.

5. The method as recited in claim 4, further comprising determining a peak emission wavelength for the second LED and a peak emission wavelength for the light source based upon the determined peak emission wavelength of the first LED.

6. The method as recited in claim 4, wherein the light source is a reference light source not contained within the group of LEDs.

7. The method as recited in claim 6, further comprising measuring photocurrent induced in the first LED by the reference light source.

8. The method as recited in claim 7, further comprising using a resistor connected across the first LED to produce a voltage from the photocurrent.

9. The method as recited in claim 8, wherein a resistance of the resistor is small enough such that the photocurrent times the resistance is substantially less than a turn on voltage of the first LED.

10. The method as recited in claim 6, further comprising producing light with approximately a single wavelength with the reference light source.

11. The method as recited in claim 10, wherein the single wavelength is longer than the peak emission wavelength of the first LED.

12. The method as recited in claim 10, wherein the single wavelength is shorter than the peak emission wavelength of the first LED.

13. The method as recited in claim 6, further comprising using the reference light source to produce light with approximately a first wavelength, measuring photocurrent induced in the first LED by the first wavelength light, using the reference light source to produce light with approximately a second wavelength different from the first wavelength, measuring photocurrent induced in the first LED by the second wavelength light, and determining a ratio of photocurrents induced in the first LED by the first and second wavelength lights.

14. The method as recited in claim 13, further comprising using two or more reference light sources to produce the different wavelength lights.

15. The method as recited in claim 13, wherein the peak emission wavelength of the first LED is known.

16. The method as recited in claim 15, further comprising determining a relationship between peak emission wavelength and the ratio of photocurrents induced in the first LED by the first and second wavelength lights.

17. The method as recited in claim 15, wherein the peak emission wavelength of the second LED is unknown.

18. The method as recited in claim 17, further comprising using the reference light source to produce light with approximately the first wavelength, measuring photocurrent induced in the second LED by the first wavelength light, using the reference light source to produce light with approximately the second wavelength, measuring photocurrent induced in the second LED by the second wavelength light, and determining a ratio of photocurrents induced in the second LED by the first and second wavelength lights wherein the unknown wavelength of the second LED is determined to be equal to the known wavelength of the first LED times the ratio of photocurrents induced in the first LED by the first and second wavelength lights divided by the ratio of photocurrents induced in the second LED by the first and second wavelength lights.

19. The method as recited in claim 18, further comprising using two or more reference light sources to produce the different wavelength lights.

20. The method as recited in claim 1, wherein the light source is a third LED contained within the group of LEDs or a reference light source not contained within the group of LEDs.

21. The method as recited in claim 1, wherein the light source is a third LED contained within the group of LEDs.

24. The method as recited in claim 21, wherein emission intensities of the second and third LEDs were previously adjusted to produce desired output intensities.

25. The method as recited in claim 24, wherein the emission intensities of the second and third LEDs were previously adjusted using a separate control device having a plurality of LEDs with known output intensities.

26. The method as recited in claim 24, wherein the steps of measuring a ratio of photocurrents, comparing the ratio of photocurrents and calibrating light produced by the group of LEDs are conducted at a second time when the emission intensities for the second and third LEDs have changed to unknown intensities.

27. The method as recited in claim 21, further comprising comparing the ratio of photocurrents induced in the first LED by the second and third LEDs to a ratio of photocurrents induced on a control device by the second and third LED, wherein the ratio of photocurrents induced on the control device by the first, second and third LEDs have known output intensities.

28. The method as recited in claim 21, wherein the first, second, and third LEDs are a red LED, a red LED, and a white LED respectively.

29. The method as recited in claim 28, further comprising using the first, second, and third LEDs within an LED lamp.

30. The method as recited in claim 28, further comprising using the first, second, and third LEDs within an LCD backlight.

31. The method as recited in claim 21, wherein the first, second, and third LEDs are a first red LED, a second red LED, and a third green LED respectively.

32. The method as recited in claim 31, further comprising using a fourth blue LED as a light source, and using the first red LED to also determine an emission intensity for the fourth blue LED, wherein the second red LED, the third green LED and the fourth blue LED are located within a first pixel and wherein the first red LED is located in an adjacent pixel.

33. The method as recited in claim 1, further comprising using a resistor connected across the first LED to produce a voltage from the ratio of photocurrents induced in the first LED.

34. The method as recited in claim 33, wherein a resistance of the resistor is small enough such that the ratio of photocurrents induced in the first LED times the resistance is substantially less than a turn on voltage of the first LED.

35. The method as recited in claim 1, further comprising using the first LED within an LCD display.

36. The method as recited in claim 1, further comprising using the first LED in an organic LED display.

37. The method as recited in claim 1, further comprising using the first LED in a digital billboard.

38. The method as recited in claim 1, further comprising using the first LED in a projector.

39. The method as recited in claim 1, wherein the light source is a reference light source not contained within the group of LEDs.

40. The method as recited in claim 39, wherein the emission intensity of the second LED was previously adjusted to produce a desired output intensity.

41. The method as recited in claim 40, wherein the emission intensity of the second LED was previously adjusted using a separate control device having a plurality of LEDs with known output intensities.

42. The method as recited in claim 40, wherein the steps of measuring a ratio of photocurrents, comparing the ratio of photocurrents, and calibrating light produced by the group of LEDs are conducted a second time when the emission intensity for the second LED has changed to an unknown intensity.

43. The method as recited in claim 42, further comprising comparing a desired ratio of photocurrents with the ratio of photocurrents induced on the first LED by the second LED and the reference light source.

22. The method as recited in 21, further comprising configuring the second LED as a photo-detector to receive light emitted by the first LED during a second time, determining an intensity emission characteristic for the first LED based upon the light received by the second LED from the first LED, using the second LED to receive light emitted by the third LED, determining an intensity emission characteristic for the third LED based upon the light received by the second LED from the third LED, and adjusting an output intensity of the first LED, the second LED, the third LED or any combination of the three LEDs based upon the determined intensity emission characteristics.

23. The method as recited in claim 22, further comprising measuring a ratio of photocurrents induced in the second LED by the first and third LEDs to determine the intensity emission characteristics for the first and third LEDs.

44. A system for calibrating light produced by a group of LEDs comprising at least a first LED and a second LED, the system comprising:

the first LED, wherein the first LED is configured as a photo-detector to receive light from the second LED and a light source during a first time; and

control circuitry configured during the first time to;

compare a ratio of photocurrents, which are induced in the first LED from the light received from the second LED and the light source, to a ratio of photocurrents of known intensities to determine a change in emission intensity associated with the second LED or the light source; and

calibrate light produced by the group of LEDs by adjusting an emission characteristic of the first LED, the second LED, or the light source based upon the determined change in emission intensity.

45. The system as recited in claim 44, wherein the first LED is configured as a light emitter to emit light along with other LEDs in the group during a second time.

46. The system as recited in claim 44, wherein the control circuitry is further configured to adjust an output intensity of the first LED, the second LED, or the light source based upon the determined change in emission intensity.

47. The system as recited in claim 44, wherein the control circuit if further configured to determine a peak emission wavelength for the first LED.

48. The system as recited in claim 47, wherein the control circuitry is further configured to determine a peak emission wavelength for the second LED or a peak emission wavelength for the light source based upon the determined peak emission wavelength the first LED.

49. The system as recited in claim 47, wherein the light source comprises at least one reference light source.

50. The system as recited in claim 49, wherein the control circuitry is configured to measure the photocurrent induced in the first LED by the reference light source.

51. The system as recited in claim 50, further comprising a resistor connected across the first LED, the resistor being configured to produce a voltage from the photocurrent.

52. The system as recited in claim 51, wherein a resistance of the resistor is small enough such that the photocurrent times the resistance is substantially less than a turn on voltage of the first LED.

53. The system as recited in claim 49, wherein the at least one reference light source is configured to produce light with approximately a single wavelength.

54. The system as recited in claim 53, wherein the single wavelength is longer than an emission wavelength of the first LED.

55. The system as recited in claim 53, wherein the single wavelength is shorter than an emission wavelength of the first LED.

56. The system as recited in claim 49, wherein the at least one reference light source is configured to produce light having a first wavelength and to produce light having a second wavelength different from the first wavelength, and wherein the control circuitry is configured to measure photocurrents induced in the first LED by the first and second wavelength lights and to determine a ratio of photocurrents induced in the first LED by the first and second wavelength lights.

57. The system as recited in claim 56, wherein the emission wavelength of the first LED is known.

58. The system as recited in claim 57, wherein the control circuitry is further configured to determine a relationship between emission wavelength and the ratio of photocurrents.

59. The system as recited in claim 57, wherein an emission wavelength of the second LED is unknown.

60. The system as recited in claim 59, wherein the control circuitry is configured to measure photocurrents induced in the second LED by the first and second wavelength lights from the at least one reference light source and to determine a ratio of photocurrents induced in the second LED by the first and second wavelength lights, wherein the unknown emission wavelength of the second LED is determined to be equal to the known wavelength of the first LED times the ratio of photocurrent induced in the first LED by the first and second wavelength lights divided by the ratio of photocurrent induced in the second LED by the first and second wavelength lights.

61. The system as recited in claim 44, wherein the light source is a third LED contained within the group of LEDs or a reference light source not contained within the group of LEDs.

62. The system as recited in claim 44, wherein the light source is a third LED contained within the group of LEDs.

65. The system as recited in claim 62, further comprising a resistor connected across the first LED, the resistor being configured to produce a voltage from the ratio of photocurrents induced in the first LED.

66. The system as recited in claim 65, wherein a resistance of the resistor is small enough such that the ratio of photocurrents times the resistance is substantially less than a turn on voltage of the first LED.

67. The system as recited in claim 62, wherein the control circuitry is further configured to compare intensity emission characteristics for the second and third LEDs to desired intensity emissions characteristics that were previously determined.

68. The system as recited in claim 67, wherein the control circuitry is further configured to compare ratios of photocurrents induced on the first LED with ratios of photocurrents associated with desired intensity emission characteristics.

69. The system as recited in claim 62, wherein the first, second, and third LEDs are a red LED, a red LED, and a white LED respectively.

70. The system as recited in claim 69, wherein the first, second, and third LEDs reside in an LED lamp.

71. The system as recited in claim 62, wherein the first, second, and third LEDs reside in an LCD backlight.

72. The system as recited in claim 62, wherein the first, second, and third LEDs are a first red LED, a second red LED, and a third green LED respectively.

73. The system as recited in claim 72, further comprising a fourth blue LED, wherein the first red LED is configured to receive light from the fourth blue LED, wherein the control circuitry is further configured to determine an intensity emission characteristic for the fourth blue LED, wherein the second red LED, the third green LED and the fourth blue LED are located within a first pixel and wherein the first red LED is located in an adjacent pixel.

74. The system as recited in claim 44, wherein the first LED resides in an LCD display.

75. The system as recited in claim 44, wherein the first LED resides in an organic LED display.

76. The system as recited in claim 44, wherein the first LED resides in a digital billboard.

77. The system as recited in claim 44, wherein the first LED resides in a projector.

78. The system as recited in claim 44, wherein the light source comprises a reference light source not contained within the group of LEDs.

79. The system as recited in claim 78, wherein the control circuitry is configured to measure a ratio of photocurrents induced in the first LED by the second LED and the reference light source.

80. The system as recited in claim 79, wherein the control circuitry is configured to compare an intensity emission characteristic for the second LED to a desired intensity characteristic that was previously determined.

81. The system as recited in claim 80, wherein the control circuitry is further configured to compare a desired ratio of photocurrents with the ratio of photocurrents induced on the first LED by the second LED and the reference light source.

63. The system as recited in 62, wherein the second LED is configured as a photo-detector to receive light from the first LED and the third LED during a second time, and wherein the control circuitry is further configured during the second time to determine emission characteristics associated with the first and third LEDs based upon the light received by the second LED from the first and third LEDs, and wherein the control circuitry is further configured to adjust an output intensity of the first LED, the second LED, the third LED or any combination of the three LEDs based upon the determined intensity emission characteristics.

64. The system as recited in claim 63, wherein the control circuitry is further configured to determine a ratio of photocurrents induced in the second LED by the first and third LEDs during the second time.

82. A controller for calibration of light produced by a group of LEDs comprising at least a first LED and a second LED, the controller comprising:

control circuitry configured to be coupled to the first LED and the second LED, wherein;

the control circuitry is configured during a first time to determine an emission characteristic associated with the second LED based upon light emitted from the second LED and received by the first LED; and

the control circuitry is configured during a second time to determine an emission characteristic associated with the first LED based upon light emitted from the first LED and received by the second LED; and

output driver circuitry configured to be coupled to the first LED and the second LED and configured to calibrate light produced by the group of LEDs by adjusting an emission characteristic of the first LED or the second LED based upon at least one of the emission characteristics determined during the first and second times.

83. The controller as recited in claim 82, wherein the determined emission characteristic is intensity.

84. The controller as recited in claim 83, wherein the control circuitry is further configured to adjust an output intensity of the first LED or the second LED based upon the determined intensity emission characteristic.

85. The controller as recited in claim 84, further comprising a third LED, wherein the control circuitry is further configured to determine an emission characteristic associated with the third LED based upon light received by the first LED or the second LED from the third LED and configured to adjust an output intensity of the first LED, the second LED, the third LED or any combination of the three LEDs based upon the determined intensity emission characteristics.

86. The controller as recited in claim 85, wherein the control circuitry is further configured during the first time to determine a ratio of photocurrents induced in the first LED by the second and third LEDs to determine the intensity emissions characteristics.

87. The controller as recited in 85, wherein during the second time the second LED is configured to receive light from the first LED and the third LED, and wherein the control circuitry is further configured during the second time to determine emission characteristics associated with the first and third LEDs based upon the light received by the second LED from the first and third LEDs, and wherein the control circuitry is further configured to adjust an output intensity of the first LED, the second LED, the third LED or any combination of the three LEDs based upon the determined intensity emission characteristics.

88. The controller as recited in claim 87, wherein the control circuitry is further configured during the second time to determine a ratio of photocurrents induced in the second LED by the first and third LEDs.

89. A controller for calibration of light produced by a group of LEDs comprising at least a first LED and a second LED, the controller comprising:

control circuitry configured to be coupled to the first LED and the second LED, the control circuitry further configured to determine an emission characteristic based upon light received by the first LED from at least one of the second LED and one or more reference light sources, wherein the control circuitry is further configured to determine a ratio of photocurrents induced in the first LED based upon light having a first peak emission wavelength and based upon light having a second peak emission wavelength, the light being emitted by the one or more reference light sources and the first and second peak emissions wavelengths being different; and

output driver circuitry configured to be coupled to the first LED to calibrate light produced by the group of LEDs by adjusting an emission characteristic of the first LED or the second LED based upon the determined emission characteristic.

90. The controller as recited in claim 89, wherein the determined emission characteristic is wavelength.

91. The controller as recited in claim 90, wherein the control circuitry is configured to determine a peak emission wavelength for the second LED based upon the determined wavelength emission characteristic.