Led luminaire with electrically adjusted color balance

• US 6,445,139 B1
• Filed: 09/15/2000
• Issued: 09/03/2002
• Est. Priority Date: 12/18/1998
• Status: Expired due to Term

• Current Assignee: Philips Lighting BV (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Pashley, Michael D., Marshall, Thomas M.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, THUY V
• Application Number:
  US09/663,050
• Time in Patent Office: 718 Days
• Field of Search: 315/291, 315/133, 315/131, 315/307, 315/360, 315/149, 315/152, 315/154, 315/158, 250/552, 250/553, 250/226, 362/800
• US Class Current: 315/291
• CPC Class Codes: F21V 23/0442 activated by means of a sensor, e.g. motion or photodetectors
• CPC Class Codes: F21V 23/0457 the sensor sensing the operating status of the lighting device, e.g. to detect failure of a light source or to provide feedback to the device
• CPC Class Codes: F21W 2111/02 for roads, paths or the like
• CPC Class Codes: F21Y 2105/10 comprising a two-dimensional array of point-like light-generating elements
• CPC Class Codes: F21Y 2113/13 comprising an assembly of point-like light sources
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: G08G 1/095 Traffic lights
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/32 Pulse-control circuits
• CPC Class Codes: H05B 45/37 Converter circuits

Abstract

A luminaire comprises an array of LEDs that include at least one LED in each of a plurality of colors. Supplied to the LEDs for each color is an electrical current that, during a measuring period, comprises a measuring drive pulse having at least a first boost portion and a turn-off portion. The LEDs relating to each color have a light output which has a nominal continuous value during ordinary operation and increases during the boost portion and is interrupted during the turn-off portion. The array has a combined light output when current is supplied to all of the LEDs in the array. A photodiode is arranged to measure the combined light output which selectively turning off the electrical current to the LEDs so that the photodiode measures the light output for each color separately in response to the measuring drive pulse. The average light output during the measuring period is substantially equal to the nominal continuous light output during the ordinary operation so as to avoid visible flickers.

Claims

1. A luminaire comprising:

an array of LEDs comprising at least one LED in each of a plurality of colors;

means for supplying electrical current to said LEDs in each said color, said electrical current having a measuring period that comprises a measuring drive pulse having at least a first boost portion and a turn-off portion, said LEDs in each said color having a light output, such that said light output has a nominal continuous value during ordinary operation and increases during said boost portion and is interrupted during said turn-off portion, and the array having a combined light output when current is supplied to all of the LEDs in the array;

a photodiode arranged to measure the light outputs of all the LEDs in the array; and

means for selectively turning off the electrical current to said LEDs so that said photodiode measures the light output for each color separately in response to said measuring drive pulse.

2. The luminaire in accordance with claim 1 wherein the average light output during the measuring period is substantially equal to the nominal continuous light output during said ordinary operation so as to avoid visible flickers.

3. The luminaire in accordance with claim 2 wherein said measuring drive pulse further comprises a second boost portion following said turn-off portion.

4. The luminaire in accordance with claim 3, wherein said first and second boost portions have the same duration and amplitude.

5. The luminaire in accordance with claim 4, wherein said first and second boost portions are 120% of said nominal continuous light value.

6. The luminaire in accordance with claim 5, wherein the duration of said first and second boost portion is approximately 5 msec and duration of said turn-off portion is approximately 2 msec.

7. The luminaire in accordance with claim 2 further comprising means for storing calibrated values associating LED drive current variations with LED light output variations.

8. A method for driving an array of LEDs comprising at least one LED in each of a plurality of colors in a luminaire comprising the steps of:

supplying electrical current to said LEDs in each said color, such that said LEDs have a light output with a nominal continuous value during ordinary operation;

boosting said electrical current during a measuring period so as to define a measuring drive pulse having at least a first boost portion;

turning-off said electrical current during said measuring period so as to define a turn-off portion, such that said light output increases during said boost portion and is interrupted during said turn-off portion, and the array having a combined light output when current is supplied to all of the LEDs in the array;

measuring the light outputs of all the LEDs in the array; and

selectively turning off the electrical current to said LEDs so as to measure the light output for each color separately in response to said measuring drive pulse.

9. The method in accordance with claim 8 further comprising the step of maintaining the average light output during the measuring period substantially equal to the nominal continuous light output during said ordinary operation so as to avoid visible flickers.

10. The method in accordance with claim 9 further comprising the step of boosting said electrical current so as to define a second boost portion following said turn-off portion.

11. The method in accordance with claim 10 further comprising the step of maintaining said first and second boost portions to have the same duration and amplitude.

12. The method in accordance with claim 11 further comprising the step of boosting said electrical current signal by 120% of said nominal continuous light value.

13. The method in accordance with claim 12 further comprising the step of maintaining the duration of said first and second boost portion to about 5 msec and maintaining the duration of said turn-off portion to about 2 msec.

14. The method in accordance with claim 9 further comprising the step of storing calibrated values associating LED drive current variations with LED light output variations.