Luminance and chromaticity control of an LCD backlight

• US 7,002,546 B1
• Filed: 05/15/2002
• Issued: 02/21/2006
• Est. Priority Date: 05/15/2002
• Status: Active Grant

• Current Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Mosier, Donald E., Johnson, Rick J., Perreault, William G., Stuppi, Albert N., Briley, Joseph H.
• Primary Examiner(s): Tran, Henry N.
• Application Number:
  US10/146,510
• Time in Patent Office: 1,378 Days
• Field of Search: 345/102, 345/82, 345/83, 345/46, 345/48, 345/39, 345/87, 345/88, 345/207, 362/30, 362/246, 362/800, 349/30, 349/61
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: Y10S 362/80 Light emitting diode

Abstract

A variably controlled LCD backlight is disclosed. The backlight includes a first light source that emits light within a first spectral power distribution and has a first radiant power output. A second light source emits light within a second spectral power distribution and has a second radiant power output. A detector detects the first and second radiant power outputs. A processor is connected to the detector and calculates chromaticity and luminance values of the emitted light based on the first and second radiant power outputs. The processor compares the calculated chromaticity and luminance values with desired chromaticity and luminance values, respectively. A controller is operationally connected to the processor and adjusts one or more of the first radiant power output and the second radiant power output in response to a difference between the calculated chromaticity and luminance values and the desired chromaticity and luminance values.

Claims

1. A variably controlled LCD backlight, comprising:

a first light source emitting light within a first spectral power distribution and having a first radiant power output;

a second light source emitting light within a second spectral power distribution and having a second radiant power output;

a detector configured to detect the first and second radiant power outputs;

a processor, connected to the detector, that calculates chromaticity and luminance values of the emitted light based on the first and second radiant power outputs, the processor further configured to compare the calculated chromaticity and luminance values with desired chromaticity and luminance values, respectively; and

a controller, operationally connected to the processor, that is configured to adjust one or more of the first radiant power output and the second radiant power output in response to a difference between the calculated chromaticity and luminance values and the desired chromaticity and luminance values.

2. The backlight of claim 1, wherein the first light source is a first array of light-emitting diodes, and wherein the second light source is a second array of light-emitting diodes.

3. The backlight of claim 2, wherein the first array of light-emitting diodes emits red light, the second array of light-emitting diodes emits green light, and further including a third array of light-emitting diodes that emits blue light at a third radiant power output;

wherein the detector is configured to detect the radiant power outputs of the first, second, and third arrays of light-emitting diodes.

4. The backlight of claim 2, wherein the first and second arrays of light-emitting diodes are selectively activated by the controller such that

for a first predetermined time, the first array is activated and the second array is not activated;

for a second predetermined time, the second array is activated and the first array is not activated; and

for a third predetermined time, the first array and the second array are activated.

5. The backlight of claim 4, wherein the detector is configured to detect the first radiant power output during the first predetermined time, and wherein the detector is configured to detect the second radiant power output during the second predetermined time.

6. The backlight of claim 4, wherein for a fourth predetermined time, neither the first array nor the second array are activated.

7. The backlight of claim 6, wherein an ambient luminance is measured during the fourth predetermined time, and wherein the measured ambient luminance is subtracted from the luminance of light detected during at least one of the first and second predetermined times.

8. The backlight of claim 1, wherein the first light source includes a first fluorescent light, and wherein the second light source includes a second fluorescent light.

9. The backlight of claim 1, wherein the detector is a first detector further configured to detect a first predetermined tri-stimulus value of light emitted by the first and second light sources, the backlight further comprising:

a second detector configured to detect a second predetermined tri-stimulus value of light emitted by the first and second light sources; and

a third detector configured to detect a third predetermined tri-stimulus value of light emitted by the first and second light sources,

wherein the processor is further connected to the second detector and the third detector and is configured to calculate chromaticity and luminance values of emitted light based on the first, second, and third predetermined tri-stimulus values detected by the first, second, and third detectors.

10. The backlight of claim 1, wherein the controller selectively adjusts the first and second radiant power outputs by varying electrical current to the first and second light sources, respectively.

11. The backlight of claim 1, wherein the controller is configured to control current to the first and second light sources using pulse-width modulation, and further wherein the first and second radiant power outputs are selectively adjusted by altering a pulse-width modulation pattern to one of the first and second light sources.

12. A method of controlling chromaticity and luminance levels of

an LCD backlight, comprising:

providing a first light source that emits light within a first spectral power distribution;

providing a second light source that emits light within a second spectral power distribution;

detecting a predetermined tri-stimulus value of light emitted by the first and second light sources;

calculating chromaticity and luminance values of the emitted light based on the predetermined tri-stimulus value;

comparing the calculated chromaticity and luminance values with desired chromaticity and luminance values, respectively; and

adjusting one or more of an intensity of the first light source and an intensity of the second light source in response to a difference between the calculated chromaticity and luminance values and the desired chromaticity and luminance values.

13. The method of claim 12 wherein the first light source and the second light source emit light such that

for a first predetermined time, the first light source is activated and the second light source is not activated;

for a second predetermined time, the second light source is activated and the first light source is not activated; and

for a third predetermined time, the first light source and the second light source are activated;

wherein the predetermined tri-stimulus value of the first light source is detected during the first predetermined time, and the predetermined tri-stimulus value of the second light source is detected during the second predetermined time.

14. The method of claim 13, further including measuring an ambient luminance during a fourth predetermined time when neither the first light source nor the second light source are activated.

15. The method of claim 12, wherein the adjusting is accomplished by adjusting an amount of electrical current powering at least one of the first light source and the second light source.

16. An optical feedback and control system for an LCD backlight having a first light source and a second light source, each of the light sources emitting light having a different spectral power distribution, the system comprising:

a detector configured to detect radiant power of light emitted by the first and second light sources;

a processor, connected to the detector, that calculates chromaticity and luminance values of the emitted light based on the detected radiant power and the spectral power distribution of each of the first and second light sources, the processor further configured to compare the calculated chromaticity and luminance values with desired chromaticity and luminance values, respectively;

a controller, operationally connected to the processor, that is configured to adjust one or more of the radiant power of the first light source and the radiant power of the second light source in response to a difference between the calculated chromaticity and luminance values and the desired chromaticity and luminance values.

17. The optical feedback and control system of claim 16, wherein the first and second light sources are selectively activated by the controller such that

for a first predetermined time, the first light source is activated and the second light source is not activated;

for a second predetermined time, the second light source is activated and the first light source is not activated; and

for a third predetermined time, the first light source and the second light source are activated.

18. The optical feedback and control system of claim 17, wherein the detector is configured to detect the radiant power of the first light source during the first predetermined time, and wherein the detector is configured to detect the radiant power of the second light source during the second predetermined time.

19. The optical feedback and control system of claim 17, wherein for a fourth predetermined time, neither the first light source nor the second light source are activated, and wherein an ambient luminance is measured during the fourth predetermined time.