IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
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출원번호 |
US-0471081
(2014-08-28)
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등록번호 |
US-9510416
(2016-11-29)
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발명자
/ 주소 |
- Dias, Alcides Jose
- Lewis, Jason E.
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출원인 / 주소 |
|
대리인 / 주소 |
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인용정보 |
피인용 횟수 :
1 인용 특허 :
132 |
초록
▼
An illumination device and method is provided herein for controlling an LED illumination device, so that a desired luminous flux and a desired chromaticity of the device can be maintained over time as the LEDs age. According to one embodiment, the method determines an expected wavelength value and a
An illumination device and method is provided herein for controlling an LED illumination device, so that a desired luminous flux and a desired chromaticity of the device can be maintained over time as the LEDs age. According to one embodiment, the method determines an expected wavelength value and an expected intensity value for each emission LED included within the illumination device at the drive current currently applied to the emission LED and the present emitter forward voltage. In addition, the method determines a photodetector responsivity for each emission LED at the expected wavelength value and the present photodetector forward voltage. The photodetector responsivity calculated for each emission LED is used as a reference for adjusting the lumen output of the emission LED to account for LED aging affects.
대표청구항
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1. A method for controlling an illumination device comprising a plurality of emission light emitting diodes (LEDs) and a photodetector, wherein the method comprises: applying respective drive currents to the plurality of emission LEDs to drive the plurality of emission LEDs substantially continuousl
1. A method for controlling an illumination device comprising a plurality of emission light emitting diodes (LEDs) and a photodetector, wherein the method comprises: applying respective drive currents to the plurality of emission LEDs to drive the plurality of emission LEDs substantially continuously to produce illumination;periodically turning the plurality of emission LEDs off for short durations of time to produce periodic intervals;measuring a forward voltage presently developed across each emission LED, one LED at a time, during a first portion of the periodic intervals; anddetermining, for each emission LED, an expected wavelength value and an expected intensity value corresponding to the forward voltage measured across the emission LED and the drive current currently applied to the emission LED by applying one or more interpolation techniques to a table of stored calibration values correlating wavelength and intensity to drive current at a plurality of different temperatures. 2. The method as recited in claim 1, wherein for each emission LED, the table of stored calibration values comprises: a first plurality of stored wavelength values, which were previously detected from the emission LED upon applying a plurality of different drive currents to the emission LED during a calibration phase when the emission LED was subjected to a first ambient temperature;a second plurality of stored wavelength values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to a second temperature, which is different than the first ambient temperature;a first plurality of stored forward voltages, which were previously measured across the emission LED before or after each of the different drive currents was applied to the emission LED during the calibration phase when the emission LED was subjected to the first ambient temperature; anda second plurality of stored forward voltages, which were previously measured across the emission LED before or after each of the different drive currents was applied to the emission LED during the calibration phase when the emission LED was subjected the second temperature. 3. The method as recited in claim 2, wherein the step of determining an expected wavelength value for each emission LED comprises: calculating a third plurality of wavelength values corresponding to the forward voltage presently measured across the emission LED by interpolating between the first plurality of stored wavelength values and the second plurality of wavelength values corresponding to the emission LED;generating a relationship between the third plurality of wavelength values; andselecting the expected wavelength value from the generated relationship that corresponds to the drive current currently applied to the emission LED. 4. The method as recited in claim 3, wherein the step of calculating the third plurality of wavelength values comprises using a linear interpolation technique to interpolate between the first and second plurality of stored wavelength values corresponding to the emission LED. 5. The method as recited in claim 3, wherein the step of generating the relationship comprises applying a linear interpolation or a non-linear interpolation to the third plurality of wavelength values to generate a linear relationship or a non-linear relationship between wavelength and drive current for the emission LED, wherein application of the linear interpolation or the non-linear interpolation is based on a color of the emission LED. 6. The method as recited in claim 3, wherein the step of generating the relationship comprises applying a piece-wise linear interpolation to the third plurality of wavelength values to approximate a non-linear relationship between wavelength and drive current for the emission LED. 7. The method as recited in claim 1, wherein for each emission LED, the table of stored calibration values further comprises: a first plurality of stored intensity values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to the first ambient temperature; anda second plurality of stored intensity values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to the second ambient temperature. 8. The method as recited in claim 7, wherein the step of determining an expected intensity value for each emission LED comprises: calculating a third plurality of intensity values corresponding to the forward voltage presently measured across the emission LED by interpolating between the first plurality of stored intensity values and the second plurality of intensity values corresponding to the emission LED;generating a relationship between the third plurality of intensity values; andselecting the expected intensity value from the generated relationship that corresponds to the drive current currently applied to the emission LED. 9. The method as recited in claim 8, wherein the step of calculating the third plurality of intensity values comprises using a linear interpolation technique to interpolate between the first and second plurality of stored intensity values corresponding to the emission LED. 10. The method as recited in claim 8, wherein the step of generating the relationship comprises applying a linear interpolation to the third plurality of intensity values to generate a linear relationship between intensity and drive current for the emission LED. 11. The method as recited in claim 8, wherein the step of generating the relationship comprises applying a piece-wise linear interpolation to the third plurality of intensity values to approximate a non-linear relationship between intensity and drive current for the emission LED. 12. The method as recited in claim 8, wherein the first, second and third plurality of intensity values comprise radiance values, and wherein the expected intensity value is an expected radiance value. 13. The method as recited in claim 8, wherein the first, second and third plurality of intensity values comprise luminance values, and wherein the expected intensity value is an expected luminance value. 14. The method as recited in claim 1, further comprising: measuring a photocurrent induced on the photodetector in response to the illumination produced by each emission LED, one emission LED at a time, and received by the photodetector during a second portion of the periodic intervals;measuring a forward voltage presently developed across the photodetector by applying a non-operative drive current to the photodetector during a third portion of the periodic intervals; andcalculating, for each emission LED, a responsivity of the photodetector using the expected wavelength value determined for the emission LED, the forward voltage presently measured across the photodetector, and a plurality of coefficient values that were generated during a calibration phase and stored within the illumination device to characterize a change in the photodetector responsivity over emitter wavelength and photodetector forward voltage. 15. The method as recited in claim 14, wherein for each emission LED, the method further comprises: calculating an intensity value for the emission LED by dividing the induced photocurrent measured during the measuring step by the photodetector responsivity calculated during the calculating step;calculating a scale factor by dividing the expected intensity value determined for the emission LED by the intensity value calculated for the emission LED;applying the scale factor to a desired luminous flux value for the emission LED to obtain an adjusted luminous flux value for the emission LED; andadjusting the drive current currently applied to the emission LED to achieve the adjusted luminous flux value. 16. An illumination device, comprising: a plurality of emission light emitting diodes (LEDs);a storage medium configured for storing a table of calibration values correlating wavelength and intensity to drive current at a plurality of different temperatures for each of the plurality of emission LEDs;an LED driver and receiver circuit configured for applying respective drive currents to the plurality of emission LEDs to drive the plurality of emission LEDs substantially continuously to produce illumination, periodically turning the plurality of emission LEDs off for short durations of time to produce periodic intervals, and applying a non-operative drive current to each emission LED, one LED at a time, during the a first portion of the periodic intervals to measure a forward voltage presently developed across each emission LED; anda control circuit configured for determining, for each emission LED, an expected wavelength value and an expected intensity value corresponding to the forward voltage presently measured across the emission LED and the drive current currently applied to the emission LED by applying one or more interpolation techniques to the table of stored calibration values. 17. The illumination device as recited in claim 16, wherein for each emission LED, the table of stored calibration values comprises: a first plurality of stored wavelength values, which were previously detected from the emission LED upon applying a plurality of different drive currents to the emission LED during a calibration phase when the emission LED was subjected to a first ambient temperature;a second plurality of stored wavelength values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to a second temperature, which is different than the first ambient temperature;a first plurality of stored forward voltages, which were previously measured across the emission LED before or after each of the different drive currents was applied to the emission LED during the calibration phase when the emission LED was subjected to the first ambient temperature; anda second plurality of stored forward voltages, which were previously measured across the emission LED before or after each of the different drive currents was applied to the emission LED during the calibration phase when the emission LED was subjected the second temperature. 18. The illumination device as recited in claim 17, wherein for each emission LED, the control circuit is configured for determining the expected wavelength value by: calculating a third plurality of wavelength values corresponding to the forward voltage presently measured across the emission LED by interpolating between the first plurality of stored wavelength values and the second plurality of wavelength values corresponding to the emission LED;generating a relationship between the third plurality of wavelength values; andselecting the expected wavelength value from the generated relationship that corresponds to the drive current currently applied to the emission LED. 19. The illumination device as recited in claim 18, wherein the control circuit is configured for calculating the third plurality of wavelength values by using a linear interpolation technique to interpolate between the first and second plurality of stored wavelength values corresponding to the emission LED. 20. The illumination device as recited in claim 18, wherein the control circuit is configured for generating the relationship by applying a linear interpolation or a non-linear interpolation to the third plurality of wavelength values to respectively generate a linear relationship or a non-linear relationship between wavelength and drive current for the emission LED, wherein application of the linear interpolation or the non-linear interpolation is based on a color of the emission LED. 21. The illumination device as recited in claim 18, wherein the control circuit is configured for generating the relationship by applying a piece-wise linear interpolation to the third plurality of wavelength values to approximate a non-linear relationship between wavelength and drive current for the emission LED. 22. The illumination device as recited in claim 1, wherein for each emission LED, the table of stored calibration values further comprises: a first plurality of stored intensity values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to the first ambient temperature; anda second plurality of stored intensity values, which were previously detected from the emission LED upon applying the plurality of different drive currents to the emission LED during the calibration phase when the emission LED was subjected to the second ambient temperature. 23. The illumination device as recited in claim 22, wherein for each emission LED, the control circuit is configured for determining the expected intensity value by: calculating a third plurality of intensity values corresponding to the forward voltage presently measured across the emission LED by interpolating between the first plurality of stored intensity values and the second plurality of intensity values corresponding to the emission LED;generating a relationship between the third plurality of intensity values; andselecting the expected intensity value from the generated relationship that corresponds to the drive current currently applied to the emission LED. 24. The illumination device as recited in claim 23, wherein the control circuit is configured for calculating the third plurality of intensity values comprises using a linear interpolation technique to interpolate between the first and second plurality of stored intensity values corresponding to the emission LED. 25. The illumination device as recited in claim 23, wherein the control circuit is configured for generating the relationship by applying a linear interpolation to the third plurality of intensity values to generate a linear relationship between intensity and drive current for the emission LED. 26. The illumination device as recited in claim 23, wherein the control circuit is configured for generating the relationship by applying a piece-wise linear interpolation to the third plurality of intensity values to approximate a non-linear relationship between intensity and drive current for the emission LED. 27. The illumination device as recited in claim 23, wherein the first, second and third plurality of intensity values comprise radiance values, and wherein the expected intensity value is an expected radiance value. 28. The illumination device as recited in claim 23, wherein the first, second and third plurality of intensity values comprise luminance values, and wherein the expected intensity value is an expected luminance value. 29. The illumination device as recited in claim 16, wherein the LED driver and receiver circuit is further configured for: measuring a photocurrent induced on the photodetector in response to the illumination produced by each emission LED, one emission LED at a time, and received by the photodetector during a second portion of the periodic intervals; andmeasuring a forward voltage presently developed across the photodetector by applying a non-operative drive current to the photodetector during a third portion of the periodic intervals. 30. The illumination device as recited in claim 29, wherein the control circuit is further configured for: calculating, for each emission LED, a responsivity of the photodetector using the expected wavelength value determined for the emission LED, the forward voltage presently measured across the photodetector, and a plurality of coefficient values that were generated during a calibration phase and stored within the illumination device to characterize a change in the photodetector responsivity over emitter wavelength and photodetector forward voltage. 31. The illumination device as recited in claim 30, wherein for each emission LED, the control circuit is further configured for: calculating an intensity value for the emission LED as a ratio of the induced photocurrent measured by the LED driver and receiver circuit over the photodetector responsivity calculated by the control circuit;calculating a scale factor by dividing the expected intensity value determined for the emission LED by the intensity value calculated for the emission LED; andapplying the scale factor to a desired luminous flux value for the emission LED to obtain an adjusted luminous flux value for the emission LED; andadjusting the drive current currently applied to the emission LED to achieve the adjusted luminous flux value.
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