Method and apparatus for sensing the color point of an RGB LED white luminary using photodiodes
First Claim
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1. A method of controlling an LED luminary including red, green and blue (RGB) light emitting diodes (LEDs) driven by forward currents to produce a mixed color light comprising the steps of:
- measuring an output signal of a filtered photodiode for each of the red, green and blue LEDs of the LED luminary;
measuring an output signal of an unfiltered photodiode for each of the red, green and blue LEDs of the LED luminary;
calculating a photodiode output signal ratio by dividing the output signal for the filtered photodiode with the output signal of the unfiltered photodiode for each of the red, green and blue LEDs;
utilizing the photodiode output signal ratio to determine chromaticity coordinates for each of the red, green and blue LEDs; and
adjusting the forward currents for each of the red, green and blue LEDs to produce a desired color light.
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Abstract
Method and apparatus for controlling an RBG based LED luminary which measures the output signals of filtered photodiodes and unfiltered photodiodes and correlates these values to chromaticity coordinates for each of the red, green and blue LEDs of the luminary. Forward currents driving the LED luminary are adjusted in accordance with differences between the chromaticity coordinates of each of the red, green and blue LEDs and chromaticity coordinates of a desired mixed color light.
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Citations
29 Claims
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1. A method of controlling an LED luminary including red, green and blue (RGB) light emitting diodes (LEDs) driven by forward currents to produce a mixed color light comprising the steps of:
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measuring an output signal of a filtered photodiode for each of the red, green and blue LEDs of the LED luminary;
measuring an output signal of an unfiltered photodiode for each of the red, green and blue LEDs of the LED luminary;
calculating a photodiode output signal ratio by dividing the output signal for the filtered photodiode with the output signal of the unfiltered photodiode for each of the red, green and blue LEDs;
utilizing the photodiode output signal ratio to determine chromaticity coordinates for each of the red, green and blue LEDs; and
adjusting the forward currents for each of the red, green and blue LEDs to produce a desired color light. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
accessing a look-up table (LUT) which includes a correlation between the photodiode output signal ratio and chromaticity coordinates for each of the red, green and blue LEDs.
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3. The method of controlling an LED luminary according to claim 2 further comprising a step of generating a LUT for each of the red, green and blue LEDs by:
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calculating a photodiode output signal ratio for each of a plurality of red, green and blue LEDs;
measuring chromaticity coordinates for each of the plurality of red, green and blue LEDs; and
determining a relationship between the calculated photodiode output signal ratio and the chromaticity coordinates for each of the red, green and blue LEDs.
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4. The method of controlling an LED luminary according to claim 1 wherein the chromaticity coordinates correspond to a CIE 1931 chromaticity coordinate system.
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5. The method of controlling an LED luminary according to claim 1 wherein the chromaticity coordinates correspond to a new RGB colorimetric system.
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6. The method of controlling an LED luminary according to claim 1 further comprising the step of:
selecting said desired color light.
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7. The method of controlling an LED luminary according to claim 6 wherein said step of selecting said desired color light includes selecting a desired color point of the LED luminary.
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8. The method of controlling an LED luminary according to claim 7 further comprising the steps of:
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pre-storing a plurality of desired color points of the LED luminary in a memory; and
selecting one of the plurality of desired color points as the desired color light.
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9. The method of controlling an LED luminary according to claim 1 wherein said adjusting step comprises the steps of:
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generating control voltages for each of the red, green and blue LEDs based on said chromaticity coordinates for each of the red, green and blue LEDs and chromaticity coordinates for the desired color light; and
applying said control voltages to LED drivers for each of the red, green and blue LEDs so as to adjust forward currents for each of the red, green and blue LEDs to produce the desired color light.
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10. The method of controlling an LED luminary according to claim 1 wherein said steps are implemented by analog circuitry.
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11. The method of controlling an LED luminary according to claim 1 wherein said steps are implemented by digital circuitry.
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12. The method of controlling an LED luminary according to claim 1 wherein the steps of measuring the output signal of a filtered photodiode and measuring the output signal of an unfiltered photodiode are carried out in predetermined time intervals.
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13. A control system for an LED luminary including red, green and blue (RGB) light emitting diodes (LEDs) driven by forward currents to produce a mixed color light, comprising:
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a feedback unit which generates feedback values representative of the mixed color light produced by said LED luminary, said feedback values corresponding to output signals of a photodiode; and
a controller operatively coupled to said feedback unit which determines a difference between said feedback values and reference values representative of a desired mixed color light, said controller adjusting at least one of control voltages and forward currents in accordance with said difference. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
said controller calculates a photodiode output signal ratio by dividing filtered photodiode output signals for said red, green and blue LEDs with unfiltered photodiode output signals for said red, green and blue LEDs respectively, utilizes the photodiode output signal ratio to determine chromaticity coordinates for each of the red, green and blue LEDs, and adjusts forward currents for each of the red, green and blue LEDs to produce the desired mixed color light.
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29. The control system for an LED luminary according to claim 28 wherein said controller determines the chromaticity coordinates for each of the red, green and blue LEDs by accessing a look-up table which includes a relationship between the photodiode output signal ratio and the chromaticity coordinates for each of the red, green and blue LEDs.
Specification