RGB led based white light control system with quasi-uniform color metric

• US 20030111533A1
• Filed: 12/19/2001
• Published: 06/19/2003
• Est. Priority Date: 12/19/2001
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Chang, Chin
• Application Number:
  US10/024,738
• Publication Number:
  US 20030111533A1
• Time in Patent Office: Days
• US Class Current: 235/454
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The present invention is directed to a color control system for generating a desired white light by a plurality of Red, Green and Blue light emitting diodes (LEDs) comprised of a sensor responsive to a white light generated by the plurality of LEDs to measure the color coordinates of the white light, where the color coordinates are defined in a first color space. A transformation module is provided coupled to the sensor to transform the coordinates of the generated white light to a second color space. A reference module configured to provide reference color coordinates corresponding to the desired white light, where the reference color coordinates are expressed in the second color space. An adder is provided coupled to the transformation module and the reference module configured to generate an error color coordinate corresponding to a difference between the desired white light color coordinates and the generated white light color coordinates. A driver module is provided coupled to the adder and configured to generate a drive signal for driving the LEDs.

Claims

1. A color control system for generating a desired white light by a plurality of Red, Green and Blue light emitting diodes (LEDs) comprising:

a sensor responsive to a white light generated by said plurality of LEDs to measure the color coordinates of said white light, wherein said color coordinates are defined in a first color space;

a transformation module coupled to said sensor to transform said coordinates of said generated white light to a second color space;

a reference module configured to provide reference color coordinates corresponding to said desired white light, wherein said reference color coordinates are expressed in said second color space;

an adder coupled to said transformation module and said reference module configured to generate an error color coordinate corresponding to a difference between said desired white light color coordinates and said generated white light color coordinates; and

a driver module coupled to said adder and configured to generate a drive signal for driving said LEDs.

2. The system in accordance with claim 1 wherein said first color space is an X,Y.Z color space.

3. The system in accordance with claim 2, wherein said second color space is a uLv color space.

4. The system in accordance with claim 1 further comprising a controller coupled to said adder, wherein said controller generates control voltage signals corresponding to said Red, Green and Blue LEDs respectively.

5. The system in accordance with claim 3 wherein said sensor is a tristimulus filter.

6. The system in accordance with claim 5 wherein said transformation module transforms said X,Y,Z color coordinates such that

L=683Y u=4X/(X+15Y+3Z) v=6Y/(X+15Y+3Z)

7. A feedback control system for controlling a plant operation comprising:

a controller portion for providing a control signal in response to an error signal, said controller portion having a first response bandwidth and a transfer function C(s) defined as C(s)=K_p+K_I/s, wherein K_p and K_I, are constant real matrices;

a plant portion for receiving said control signal and generating an output signal, said plant portion having a second response bandwidth, and a DC gain matrix defined as G, wherein said first response bandwidth is smaller than said second response bandwidth;

a feedback portion for measuring said desired output signal having a DC gain matrix defined as Q; and

an adder coupled to said feedback portion configured to measure said error signal based on said measured output signal and a desired input signal such that

Re{(eig((I−

GK_pQ)<sup>−

1</sup>GK_IQ)}<

0,

wherein Re {eig . . . } stands for the real part of the eigen value of the matrix, and I is the identity matrix.

8. The system in accordance with claim 7, wherein said plant portion comprises an RGB LED driver module coupled to an RGB luminary module.

9. The system in accordance with claim 8, wherein said feedback portion comprises a sensor coupled to said luminary module;

a color point identification module for transforming values received form said filter to a first color space value system; and

a transformation module for transforming signals received by said identification module to a second color space value system.

10. The system in accordance with claim 9 wherein said first color space is an X,Y.Z color space.

11. The system in accordance with claim 10, wherein said second color space is a uLv current space.

12. The system in accordance with claim 9, wherein said controller portion generates control voltage signals corresponding to said Red, Green and Blue LEDs respectively.

13. The system in accordance with claim 12 wherein said sensor is a tristimulus filter.

14. The system in accordance with claim 13 wherein said transformation module transforms said X,Y,Z color coordinates such that

L=683Y u=4X/(X+15Y+3Z) v=6Y/(X+15Y+3Z).

15. A method in a control system for generating a desired white light by a plurality of Red, Green and Blue light emitting diodes (LEDs) comprising the steps of:

sensing a white light generated by said plurality of LEDs to measure the color coordinates of said white light, wherein said color coordinates are defined in a first color space;

transforming said coordinates of said generated white light to a second color space;

providing reference color coordinates corresponding to said desired white light, wherein said reference color coordinates are expressed in said second color space;

generating an error color coordinate corresponding to a difference between said desired white light color coordinates and said generated white light color coordinates; and

generating a drive signal for driving said LEDs.

16. The method in accordance with claim 15 further comprising the step of defining said first color space as an X,Y.Z color space.

17. The method in accordance with claim 15, further comprising the step of defining said second color space as a uLv current space.

18. The method in accordance with claim 15 further comprising the step of generating control voltage signals corresponding to said Red, Green and Blue LEDs respectively.

19. The method in accordance with claim 18 wherein said step of transforming said X,Y,Z color coordinates further comprises the step of assigning values in accordance with

L=683Y u=4X/(X+15Y+3Z) v=6Y/(X+15Y+3Z)