Illumination device and method for calibrating an illumination device over changes in temperature, drive current, and time
First Claim
1. An illumination device, comprising:
- a plurality of light emitting diode (LED) chains configured to produce illumination for the illumination device;
a photodetector configured for detecting the illumination produced by each of the plurality of LED chains;
an LED driver and receiver circuit configured for;
successively applying at least three different drive currents to each of the plurality of LED chains, one LED chain at a time, to produce illumination at different levels of brightness when the LED chains are subjected to a first ambient temperature;
measuring photocurrents induced on the photodetector by the illumination produced by each of the plurality of LED chains at each of the at least three different drive currents;
measuring forward voltages that develop across the photodetector before, during or after each induced photocurrent is measured; and
repeating the steps of successively applying at least three different drive currents to each of the LED chains, measuring photocurrents induced on the photodetector, and measuring forward voltages that develop across the photodetector when the LED chains are subjected to a second ambient temperature, which is different from the first ambient temperature;
an interface configured for receiving luminous flux and chromaticity measurements, which are measured by an external calibration tool upon receiving the illumination produced by each of the plurality of LED chains at each of the at least three different drive currents when the LED chains are subjected to the first and second ambient temperatures; and
a storage medium configured for storing the photocurrent, forward voltage, luminous flux, and chromaticity measurements obtained for each of the plurality of LED chains within a table of calibration values.
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Accused Products
Abstract
An illumination device and method is provided herein for calibrating individual LEDs in the illumination device, so as to obtain a desired luminous flux and a desired chromaticity of the device over changes in drive current, temperature, and over time as the LEDs age. The calibration method may include subjecting the illumination device to a first ambient temperature, successively applying at least three different drive currents to a first LED to produce illumination at three or more different levels of brightness, obtaining a plurality of optical measurements from the illumination produced by the first LED at each of the at least three different drive currents, obtaining a plurality of electrical measurements from the photodetector and storing results of the obtaining steps within the illumination device to calibrate the first LED at the first ambient temperature. The plurality of optical measurements may generally include luminous flux and chromaticity, the plurality of electrical measurements may generally include induced photocurrents and forward voltages, and the calibration method steps may be repeated for each LED included within the illumination device and upon subjecting the illumination device to a second ambient temperature.
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Citations
17 Claims
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1. An illumination device, comprising:
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a plurality of light emitting diode (LED) chains configured to produce illumination for the illumination device; a photodetector configured for detecting the illumination produced by each of the plurality of LED chains; an LED driver and receiver circuit configured for; successively applying at least three different drive currents to each of the plurality of LED chains, one LED chain at a time, to produce illumination at different levels of brightness when the LED chains are subjected to a first ambient temperature; measuring photocurrents induced on the photodetector by the illumination produced by each of the plurality of LED chains at each of the at least three different drive currents; measuring forward voltages that develop across the photodetector before, during or after each induced photocurrent is measured; and repeating the steps of successively applying at least three different drive currents to each of the LED chains, measuring photocurrents induced on the photodetector, and measuring forward voltages that develop across the photodetector when the LED chains are subjected to a second ambient temperature, which is different from the first ambient temperature; an interface configured for receiving luminous flux and chromaticity measurements, which are measured by an external calibration tool upon receiving the illumination produced by each of the plurality of LED chains at each of the at least three different drive currents when the LED chains are subjected to the first and second ambient temperatures; and a storage medium configured for storing the photocurrent, forward voltage, luminous flux, and chromaticity measurements obtained for each of the plurality of LED chains within a table of calibration values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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Specification