Regulation of Wavelength Shift and Perceived Color of Solid State Lighting with Temperature Variation

• US 20090079358A1
• Filed: 10/29/2007
• Published: 03/26/2009
• Est. Priority Date: 09/21/2007
• Status: Active Grant

• Current Assignee: Chemtron Research LLC (Intellectual Ventures LLC)
• Original Assignee: Exclara, Inc. (Million Star Technology Ltd.)
• Inventors: Rodriguez, Harry, Shteynberg, Anatoly, Zhou, Dongsheng, Lehman, Bradley M.
• Granted Patent: US 8,264,448 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 45/24 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/28 using temperature feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

Exemplary embodiments of the invention provide a system, apparatus, and method of controlling an intensity and spectrum of light emitted from a solid state lighting system. The solid state lighting has a first emitted spectrum at full intensity and at a selected temperature, with a first electrical biasing for the solid state lighting producing a first wavelength shift, and a second electrical biasing for the solid state lighting producing a second, opposing wavelength shift. Exemplary embodiments provide for receiving information designating a selected intensity level or a selected temperature; and providing a combined first electrical biasing and second electrical biasing to the solid state lighting to generate emitted light having the selected intensity level and having a second emitted spectrum within a predetermined variance of the first emitted spectrum over a predetermined range of temperatures.

Claims

1. An illumination control method for solid state lighting system with compensation for spectral changes due to temperature variation, the solid state lighting having a first emitted spectrum at a selected intensity and at a selected temperature, a first electrical biasing for the solid state lighting producing a first wavelength shift, a second electrical biasing for the solid state lighting producing a second, opposing wavelength shift, the method comprising:

determining a temperature associated with the solid state lighting; and

providing a combined first electrical biasing and second electrical biasing to the solid state lighting to generate emitted light having a second emitted spectrum over a predetermined range of temperatures and within a predetermined variance of the first emitted spectrum.

2. The method of claim 1, wherein the predetermined variance is substantially zero.

3. The method of claim 1, wherein the predetermined variance is a selected tolerance level.

4. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is a superposition of the first electrical biasing and the second electrical biasing.

5. The method of claim 4, wherein the superposition of the first electrical biasing and the second electrical biasing is at least one predetermined parameter to produce the second emitted spectrum within the predetermined variance for the selected intensity level and predetermined range of temperatures.

6. The method of claim 4, wherein the combined first electrical biasing and second electrical biasing comprises a superposition of a symmetric or asymmetric AC signal on a DC signal having an average component.

7. The method of claim 4, wherein the combined first electrical biasing and second electrical biasing has a duty cycle and an average current level, and wherein the duty cycle and the average current level are parameters stored in a memory and correspond to the predetermined range of temperatures.

8. The method of claim 4, wherein the combined first electrical biasing and second electrical biasing is a superposition of or an alternation between at least two of the following types of electrical biasing:

pulse width modulation, constant current regulation, pulse frequency modulation; and

pulse amplitude modulation.

9. The method of claim 1, further comprising:

cooling the solid state lighting to maintain the second emitted spectrum within the predetermined variance.

10. The method of claim 1, further comprising:

reducing the intensity of the light emitted from the solid state lighting to maintain the second emitted spectrum within the predetermined variance.

11. The method of claim 1, wherein the determination of the temperature associated with the solid state lighting further comprises:

sensing a junction temperature associated with the solid state lighting.

12. The method of claim 1, wherein the determination of the temperature associated with the solid state lighting further comprises:

sensing a temperature of a device associated with the solid state lighting.

13. The method of claim 12, wherein the device is a heat sink or an enclosure for the solid state lighting.

14. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is an alternation of the first electrical biasing and the second electrical biasing.

15. The method of claim 14, wherein the first electrical biasing is pulse width modulation having a first duty cycle lower than a duty cycle at full intensity and the second electrical biasing is constant current regulation having a first average current level lower than a full intensity current level.

16. The method of claim 14, wherein the first electrical biasing is provided for a first modulation period and wherein the second electrical biasing is provided for a second modulation period.

17. The method of claim 16, wherein the first duty cycle, the first average current level, the first modulation period and the second modulation period are predetermined parameters to produce the second emitted spectrum within the predetermined variance for the predetermined range of temperatures.

18. The method of claim 17, wherein the first and second modulation periods are a corresponding number of clock cycles.

19. The method of claim 14, wherein the solid state lighting comprises at least one light emitting diode (“

LED”

), and wherein the alternating first electrical biasing and second electrical biasing is provided during at least one of the following;

within a single dimming cycle of a switch mode LED driver, alternately every dimming cycle of the switch mode LED driver, alternately every second dimming cycle of the switch mode LED driver, alternately every third dimming cycle of the switch mode LED driver, alternately an equal number of consecutive dimming cycle of the switch mode LED driver, or alternately an unequal number of consecutive dimming cycle of the switch mode LED driver.

20. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is predetermined from a statistical characterization of the solid state lighting in response to a plurality of temperature levels.

21. The method of claim 20, wherein the combined first electrical biasing and second electrical biasing is further predetermined from a statistical characterization of the solid state lighting in response to the first electrical biasing and the second electrical biasing at a plurality of intensity levels.

22. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is determined in real time from at least one linear equation to produce the second emitted spectrum within the predetermined variance for the predetermined range of temperatures.

23. The method of claim 1, wherein the solid state lighting comprises at least one light emitting diode (“

LED”

).

24. The method of claim 23, wherein the first electrical biasing and the second electrical biasing are a forward current or an LED bias voltage.

25. The method of claim 23, further comprising:

synchronizing the combined first electrical biasing and second electrical biasing with a switching cycle of a switch mode LED driver.

26. The method of claim 19, further comprising:

modifying the combined first electrical biasing and second electrical biasing in response to the selected intensity level.

27. The method of claim 26, further comprising:

receiving an input signal selecting the intensity level.

28. The method of claim 1, wherein the first and second wavelength shifts are determined as corresponding first and second peak wavelengths of the emitted spectrum.

29. The method of claim 1, wherein the providing of the combined first electrical biasing and second electrical biasing further comprises:

processing a plurality of operational parameters into corresponding electrical biasing control signals; and

providing the corresponding electrical biasing control signals to a driver circuit; and

operating the driver circuit with a time averaging modulation of forward current conforming to the corresponding electrical biasing control signals to provide the selected intensity level within a dimming cycle of the driver circuit.

30. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is pulse width modulation with a peak current in a high state and an average current level at a low state.

31. The method of claim 1, wherein the combined first electrical biasing and second electrical biasing is an asymmetric or symmetric AC signal with a positive average current level.

32. The method of claim 1, wherein the solid state lighting comprises a plurality of arrays of light emitting diodes, and wherein the step of providing a combined first electrical biasing and second electrical biasing to the solid state lighting further comprises:

separately providing a corresponding combined first electrical biasing and second electrical biasing to each array of the plurality of arrays of light emitting diodes to generate an overall second emitted spectrum over the predetermined range of temperatures and within the predetermined variance of the first emitted spectrum.

33. The method of claim 32, wherein each combined first electrical biasing and second electrical biasing corresponds to a type of light emitting diode comprising the corresponding array of the plurality of arrays of light emitting diodes.

34. The method of claim 32, wherein at least three arrays of the plurality of arrays of light emitting diodes have corresponding emission spectra of different colors.

35. The method of claim 32, further comprising:

modifying a temperature of a selected array of the plurality of arrays of light emitting diodes to maintain the overall second emitted spectrum within the predetermined variance of the first emitted spectrum.

36. The method of claim 1, further comprising:

predicting a spectral response of the solid state lighting in response to the combined first electrical biasing and second electrical biasing over the predetermined range of temperatures.

37. An illumination control apparatus for a solid state lighting system with compensation for spectral changes due to temperature variation, the apparatus couplable to the solid state lighting, the solid state lighting having a first emitted spectrum at a selected intensity and at a selected temperature, a first electrical biasing for the solid state lighting producing a first wavelength shift, a second electrical biasing for the solid state lighting producing a second, opposing wavelength shift, the apparatus comprising:

a memory adapted to store a plurality of parameters corresponding to a predetermined range of temperatures; and

a controller coupled to the memory, the controller adapted to determine a temperature associated with the solid state lighting, to retrieve from the memory at least one parameter of the plurality of parameters corresponding to the determined temperature, and to convert the at least one parameter into a corresponding control signal to provide a combined first electrical biasing and second electrical biasing to the solid state lighting to generate emitted light having a second emitted spectrum over the predetermined range of temperatures and within a predetermined variance of the first emitted spectrum.

38. The apparatus of claim 37, wherein the predetermined variance is substantially zero.

39. The apparatus of claim 37, wherein the predetermined variance is a selected tolerance level.

40. The apparatus of claim 37, wherein the control signal provides the combined first electrical biasing and second electrical biasing as a superposition of the first electrical biasing and the second electrical biasing.

41. The apparatus of claim 37, wherein the control signal provides the combined first electrical biasing and second electrical biasing as superposition of a symmetric or asymmetric AC signal on a DC signal having an average component.

42. The apparatus of claim 37, wherein the plurality of parameters comprise a duty cycle parameter and an average current level parameter for the combined first electrical biasing and second electrical biasing.

43. The apparatus of claim 37, wherein the combined first electrical biasing and second electrical biasing is a superposition of or an alternation between at least two of the following types of electrical biasing:

pulse width modulation, constant current regulation, pulse frequency modulation; and

pulse amplitude modulation.

44. The apparatus of claim 37, wherein the controller is further adapted to generate a second control signal to a cooling element coupled to the solid state lighting to cool the solid state lighting to maintain the second emitted spectrum within the predetermined variance.

45. The apparatus of claim 37, wherein the controller is further adapted to generate a second control signal to reduce the intensity of the light emitted from the solid state lighting to maintain the second emitted spectrum within the predetermined variance.

46. The apparatus of claim 37, wherein the controller is further adapted to determine the temperature associated with the solid state lighting in response to a temperature signal received from a junction temperature sensor associated with the solid state lighting.

47. The apparatus of claim 37, wherein the controller is further adapted to determine the temperature associated with the solid state lighting in response to a temperature signal received from a device temperature sensor associated with the solid state lighting.

48. The apparatus of claim 47, wherein the device is a heat sink or an enclosure for the solid state lighting.

49. The apparatus of claim 37, wherein the control signal provides the combined first electrical biasing and second electrical biasing as an alternation of the first electrical biasing and the second electrical biasing.

50. The apparatus of claim 49, wherein the first electrical biasing is pulse width modulation having a first duty cycle lower than a duty cycle at full intensity and the second electrical biasing is constant current regulation having a first average current level lower than a full intensity current level.

51. The apparatus of claim 50, wherein the first electrical biasing is provided for a first modulation period and wherein the second electrical biasing is provided for a second modulation period, and wherein the first duty cycle, the first average current level, the first modulation period and the second modulation period are predetermined and stored in memory as the plurality of parameters to produce the second emitted spectrum within the predetermined variance for the determined temperature.

52. The apparatus of claim 42, wherein the solid state lighting comprises at least one light emitting diode (“

LED”

), wherein the apparatus is couplable to a switch mode LED driver, and wherein the alternating first electrical biasing and second electrical biasing is provided during at least one of the following;

within a single dimming cycle of the switch mode LED driver, alternately every dimming cycle of the switch mode LED driver, alternately every second dimming cycle of the switch mode LED driver, alternately every third dimming cycle of the switch mode LED driver, alternately an equal number of consecutive dimming cycle of the switch mode LED driver, or alternately an unequal number of consecutive dimming cycle of the switch mode LED driver.

53. The apparatus of claim 37, wherein the plurality of parameters are predetermined from a statistical characterization of the solid state lighting in response to a plurality of temperature levels.

54. The apparatus of claim 53, wherein the plurality of parameters are further predetermined from a statistical characterization of the solid state lighting in response to the first electrical biasing and the second electrical biasing at a plurality of intensity levels.

55. The apparatus of claim 37, wherein the plurality of parameters comprise at least one linear equation, and wherein the controller is further adapted to generate the control signal in real time from the at least one linear equation to provide the combined first electrical biasing and second electrical biasing to produce the second emitted spectrum within the predetermined variance for the predetermined range of temperatures.

56. The apparatus of claim 37, wherein the solid state lighting comprises at least one light emitting diode (“

LED”

).

57. The apparatus of claim 56, wherein the first electrical biasing and the second electrical biasing are a forward current or an LED bias voltage.

58. The apparatus of claim 56, wherein the controller is further adapted to synchronize the control signal with a switching cycle of a switch mode LED driver.

59. The apparatus of claim 37, wherein the solid state lighting comprises a plurality of arrays of light emitting diodes, and wherein the controller is further adapted to generate separate, corresponding control signals to provide a corresponding combined first electrical biasing and second electrical biasing to each array of the plurality of arrays of light emitting diodes to generate an overall second emitted spectrum within the predetermined variance of the first emitted spectrum and over the predetermined range of temperatures.

60. The apparatus of claim 59, wherein each combined first electrical biasing and second electrical biasing corresponds to a type of light emitting diode comprising the corresponding array of the plurality of arrays of light emitting diodes.

61. The apparatus of claim 60, wherein at least three arrays of the plurality of arrays of light emitting diodes have corresponding emission spectra of different colors.

62. The apparatus of claim 60, wherein the controller is further adapted to generate a second control signal to modify a temperature of a selected array of the plurality of arrays of light emitting diodes to maintain the overall second emitted spectrum within the predetermined variance of the first emitted spectrum and over the predetermined range of temperatures.

63. The apparatus of claim 37, wherein the solid state lighting comprises a plurality of arrays of light emitting diodes coupled to a corresponding plurality of driver circuits, and wherein the apparatus further comprises:

a plurality of controllers, each controller of the plurality of controllers couplable to a corresponding driver circuit, and each controller further adapted to generate a separate, corresponding control signal to the corresponding driver circuit to provide a corresponding combined first electrical biasing and second electrical biasing to the corresponding array of the plurality of arrays of light emitting diodes to generate an overall second emitted spectrum within the predetermined variance of the first emitted spectrum over the predetermined range of temperatures.

64. The apparatus of claim 63, wherein each combined first electrical biasing and second electrical biasing corresponds to a type of light emitting diode comprising the corresponding array of the plurality of arrays of light emitting diodes.

65. The apparatus of claim 63, wherein at least three arrays of the plurality of arrays of light emitting diodes have corresponding emission spectra of different colors.

66. A solid state lighting system, comprising:

a plurality of arrays of light emitting diodes having a first emitted spectrum at a selected intensity, a first electrical biasing for at least one array of the plurality of arrays producing a first wavelength shift, a second electrical biasing for the at least one array of the plurality of arrays producing a second, opposing wavelength shift;

a temperature sensor coupled to at least one array of the plurality of arrays of light emitting diodes;

a plurality of driver circuits, each driver circuit coupled to a corresponding array of the plurality of arrays of light emitting diodes;

an interface adapted to receive information designating the selected intensity;

a memory adapted to store a plurality of parameters corresponding to a predetermined range of temperatures; and

at least one controller coupled to the memory and to a first driver circuit of the plurality of driver circuits, the controller adapted to receive a temperature signal associated with the solid state lighting, to retrieve from the memory at least one parameter of the plurality of parameters corresponding to the temperature signal, and to convert the at least one parameter into a corresponding control signal to the first driver circuit to provide a combined first electrical biasing and second electrical biasing to the solid state lighting to generate emitted light having a second emitted spectrum over the predetermined range of temperatures and within a predetermined variance of the first emitted spectrum.

67. The system of claim 66, wherein the predetermined variance is substantially zero or is a selected tolerance level.

68. The system of claim 66, wherein the control signal provides the combined first electrical biasing and second electrical biasing as a superposition of or an alternation between at least two of the following types of electrical biasing:

pulse width modulation, constant current regulation, pulse frequency modulation; and

pulse amplitude modulation.

69. The system of claim 66, wherein the plurality of parameters comprise a duty cycle parameter and an average current level parameter for the combined first electrical biasing and second electrical biasing.

70. The system of claim 66, wherein the at least one controller is further adapted to synchronize the control signal with a switching cycle of the first driver circuit.

71. The system of claim 66, wherein the at least one controller is further adapted to modify the corresponding control signal in response to the selected intensity.

72. The system of claim 66, further comprising:

a cooling element coupled to a selected array of the plurality of arrays of light emitting diodes;

and wherein the at least one controller is further adapted to generate a second control signal to the cooling element to lower a temperature of the at least one array to maintain the overall second emitted spectrum within the predetermined variance of the first emitted spectrum.

73. The system of claim 66, wherein the at least one controller is further adapted to generate a second control signal to reduce the intensity of the light emitted from at least one array of the plurality of arrays of light emitting diodes to maintain the second emitted spectrum within the predetermined variance.

74. The system of claim 66, wherein the temperature sensor is adapted to determine a junction temperature of the at least one array of the plurality of arrays of light emitting diodes.

75. The system of claim 66, wherein the temperature sensor is adapted to determine a device temperature of the at least one array of the plurality of arrays of light emitting diodes.

76. The system of claim 75, wherein the device is a heat sink or an enclosure for the solid state lighting.

77. The system of claim 66, wherein the system further comprises:

a plurality of controllers, each controller of the plurality of controllers coupled to a corresponding driver circuit, and each controller further adapted to generate a separate, corresponding control signal to the corresponding driver circuit to provide a corresponding combined first electrical biasing and second electrical biasing to the corresponding array of the plurality of arrays of light emitting diodes to generate an overall second emitted spectrum within the predetermined variance of the first emitted spectrum.

78. The system of claim 66, wherein each combined first electrical biasing and second electrical biasing corresponds to a type of light emitting diode comprising the corresponding array of the plurality of arrays of light emitting diodes.

79. The system of claim 66, wherein the plurality of arrays of light emitting diodes comprise at least one array of red light emitting diodes, at least one array of green light emitting diodes, and at least one array of blue light emitting diodes.

80. A solid state lighting system, comprising:

a plurality of arrays of light emitting diodes, a first array of the plurality of arrays having a first emitted spectrum at full intensity, a first electrical biasing for the first array of the plurality of arrays producing a first wavelength shift, a second electrical biasing for the first array of the plurality of arrays producing a second, opposing wavelength shift;

a temperature sensor coupled to the first array of the plurality of arrays of light emitting diodes;

at least one driver circuit coupled to the first array of the plurality of arrays of light emitting diodes;

an interface adapted to receive information designating a selected intensity level lower than full intensity;

a memory adapted to store a plurality of parameters corresponding to a predetermined range of temperatures; and

at least one controller coupled to the memory and to the at least one driver circuit, the controller adapted to receive a temperature signal associated with the solid state lighting, to retrieve from the memory at least one parameter of the plurality of parameters corresponding to the temperature signal, and to convert the at least one parameter into a corresponding control signal to the at least one driver circuit to provide a combined first electrical biasing and second electrical biasing to the solid state lighting to generate emitted light having a second emitted spectrum over the predetermined range of temperatures and within a predetermined variance of the first emitted spectrum.

81. The system of claim 80, wherein the predetermined variance is substantially zero or is a selected tolerance level.

82. The system of claim 80, wherein the second emitted spectrum is an overall color generated within the predetermined variance, or a sequence of a single color emitted at a given time, or a dynamic lighting effect as requested by a second signal received by the interface.

83. The system of claim 80, wherein the control signal provides the combined first electrical biasing and second electrical biasing as a superposition of or an alternation between at least two of the following types of electrical biasing:

pulse width modulation, constant current regulation, pulse frequency modulation; and

pulse amplitude modulation.

84. The system of claim 80, wherein the plurality of parameters comprise a duty cycle parameter and an average current level parameter for the combined first electrical biasing and second electrical biasing.

85. The system of claim 80, wherein the at least one controller is further adapted to synchronize the control signal with a switching cycle of the at least one driver circuit.

86. The system of claim 80, wherein the plurality of parameters further correspond to a plurality of intensity levels.

87. The system of claim 86, wherein the at least one controller is further adapted to select corresponding parameters and to provide the corresponding control signal in response to a selected intensity level of the plurality of intensity levels.

88. The system of claim 80, wherein the system further comprises:

a plurality of driver circuits, each driver circuit of the plurality of driver circuits coupled to a corresponding array of the plurality of arrays of light emitting diodes; and

wherein the at least one controller is coupled to each driver circuit, and is further adapted to generate separate, corresponding control signal to the corresponding driver circuit to provide a corresponding combined first electrical biasing and second electrical biasing to the corresponding array of the plurality of arrays of light emitting diodes to generate a corresponding second emitted spectrum over the predetermined range of temperatures and within the predetermined variance of the corresponding first emitted spectrum.

89. The system of claim 80, wherein the system further comprises:

a plurality of driver circuits, each driver circuit of the plurality of driver circuits coupled to a corresponding array of the plurality of arrays of light emitting diodes; and

a plurality of controllers, each controller of the plurality of controllers coupled to a corresponding driver circuit, and each controller further adapted to generate separate, corresponding control signal to the corresponding driver circuit to provide a corresponding combined first electrical biasing and second electrical biasing to the corresponding array of the plurality of arrays of light emitting diodes to generate a corresponding second emitted spectrum over the predetermined range of temperatures and within the predetermined variance of the corresponding first emitted spectrum.

90. The system of claim 80, wherein each combined first electrical biasing and second electrical biasing corresponds to a type of light emitting diode comprising the corresponding array of the plurality of arrays of light emitting diodes.

91. The system of claim 80, wherein the plurality of arrays of light emitting diodes comprise at least one array of red light emitting diodes, at least one array of green light emitting diodes, and at least one array of blue light emitting diodes.

92. The system of claim 80, further comprising:

a cooling element coupled to at least one array of the plurality of arrays of light emitting diodes; and

wherein the controller is further adapted to generate a second control signal to the cooling element to lower a temperature of the at least one array to maintain the overall second emitted spectrum within the predetermined variance of the first emitted spectrum.

93. The system of claim 80, wherein the at least one controller further comprises:

a dimming frame register;

an intensity register;

a programmable look up table memory;

a programmable frame counter and cycle counter;

a block of operational signal registers;

at least one analog multiplexer; and

at least one digital-to-analog converter.

94. The system of claim 93, wherein the at least one controller is further adapted to program the operational signal registers with at least two peak current amplitude values, at least two current amplitude modulation values, and two current duty cycle values to provide the at least one input operational control signal to the driver circuit to provide the combination of the first electrical biasing and the second electrical biasing for the selected intensity level and emission wavelength control specified by the user interface.

95. The system of claim 94, wherein the at least one controller is further adapted to vary the intensity of the at least one or more substantially similar light emitting diodes without substantial optical output flickering by alternatively multiplexing the at least one input operational control signal to the driver circuit from a first set of operational signal registers synchronously to an end of a current dimming frame counter while programming asynchronously a second set of operational signal registers with a second input operational control signal.

96. The system of claim 95, wherein the at least one controller is further adapted to queue the second input operational control signal to a current status at the end of the current dimming frame counter.

97. An apparatus for controlling an emitted spectrum from an array of light emitting diodes, the apparatus couplable to the array having a first emitted spectrum at a selected intensity and at a selected temperature, a first electrical biasing for the array producing a first wavelength shift, a second electrical biasing for the array producing a second, opposing wavelength shift, the apparatus comprising:

an interface adapted to receive information designating the selected intensity level lower than full intensity;

a memory adapted to store a plurality of parameters corresponding to a plurality of intensity levels and a plurality of temperatures, at least one parameter of the plurality of parameters corresponding to the selected intensity level and a sensed or determined temperature; and

a controller coupled to the memory, the controller adapted to retrieve from the memory the at least one parameter and to convert the at least one parameter into a corresponding control signal to provide a combined first electrical biasing and second electrical biasing to the array to generate emitted light having the selected intensity level and having a second emitted spectrum within a predetermined variance of the first emitted spectrum over a predetermined range of temperatures.