LED backlight luminance sensing for LCDs

• US 20030043107A1
• Filed: 09/05/2001
• Published: 03/06/2003
• Est. Priority Date: 09/05/2001
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Feldman, Alan S., Ruby, Joseph H.
• Granted Patent: US 7,855,708 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A liquid crystal display (LCD) system having LED backlight luminance sensing is disclosed. An array of LEDs in a backlighting position includes a plurality of LED strings. At least one LED from at least one string is identified as a sampling LED. The light emitted from the sampling LED is detected via an optical path using a light sensor. The reading from the sensor is contrast with a command, which results in a power compensation to the array accordingly. In one embodiment, the system includes a sampling enclosure encasing the sampling LED and light sensor. The sampling LED'"'"'s direction of emission is altered from the string and reflected from the inside of the enclosure. In another embodiment, the system includes a direct sensing optical path between the light sensor and the sampling LED.

Claims

1. An LED luminance sensing system comprising:

a string of LEDs having a sampling LED, said string coupled to a power source such that each LED of said string receives substantially the same current;

a light sensor configured to detect light from said sampling LED;

an optical path between said sampling LED and said light sensor, said optical path configured to prevent intrusion of light not emitted from said sampling LED; and

a control mechanism in communication with said light sensor and said power source, said control mechanism configured to adjust the current to said string in accordance with the light detected from said sampling LED.

2. The LED luminance sensing system of claim 1, wherein said light sensor directly detects the light from said sampling LED.

3. The LED luminance sensing system of claim 1, further comprising a sampling enclosure surrounding said sampling LED and said light sensor.

4. The LED luminance sensing system of claim 3, wherein said optical path comprises directly sensed light from said sampling LED and light reflected from an inside wall of said sampling enclosure.

5. The LED luminance sensing system of claim 1, wherein a direction of light emission from said sampling LED is altered from the remaining LEDs of said string.

6. The LED luminance sensing system of claim 1, wherein said control mechanism configured to receive a reference point and to compare said reference point with said light detected from said sampling LED to determine whether to increase or decrease the current to said string.

7. The LED luminance sensing system of claim 1, further comprising a second sampling LED from said string.

8. The LED luminance sensing system of claim 1, further comprising a plurality of strings wherein some of said strings have a sampling LED.

9. The LED luminance sensing system of claim 8, comprising a string of red LEDs, a string of blue LEDs, and a string of green LEDs.

10. The LED luminance sensing system of claim 9, comprising a sampling LED from said string of red LEDs, a sampling LED from said string of blue LEDs, and a sampling LED from said string of green LEDs.

11. An LED luminance sensing system comprising:

at least one sampling LED in connection with a string of LEDs, said sampling LED positioned to emit light in a direction different from said string;

a sampling enclosure substantially encasing said sampling LED;

a light sensing device within said sampling enclosure, said light sensing device configured to detect light emitting from said sampling LED; and

a feedback control circuit in communication with said light sensing device, said control circuit configured to generate a command to adjust the luminance of said string in response to said light sensing device detected light.

12. The LED luminance sensing system of claim 11, wherein said sampling LED is positioned to emit light in a direction approximately 180 degrees from the remaining LEDs of said string.

13. The LED luminance sensing system of claim 11, further comprising a second sampling LED.

14. A method for sensing LED luminance, said method comprising the steps of:

providing a plurality of LEDs connected in series such that each of the LEDs receives substantially the same current and emits light at substantially the same intensity;

forming an optical path for light detection from at least one LED, said optical path positioned to substantially prevent intrusion of light not emitted from said at least one LED;

detecting the light emitted from said LED along said optical path; and

adjusting the intensity of said LED and said plurality of LEDs in response to said detecting step.

15. The method of claim 14, wherein said forming step comprises enclosing said LED in a light sampling enclosure.

16. The method of claim 15, further comprising the step of altering the emission direction of said LED in relation to said plurality of LEDs.

17. The method of claim 14, wherein said forming step comprises forming an aperture.

18. A luminance adjusting method for LED backlighting in a LCD system, said method comprising the steps of:

positioning an array of LEDs in backlighting relationship to a LCD panel, said array comprising a plurality of LED strings, each of said strings comprising a plurality of LEDs electrically connected in series;

identifying a sampling LED from one of said strings;

detecting an illumination of said sampling LED;

comparing said illumination to a reference; and

adjusting a luminance of said LCD system in response to said comparing step.

19. The method of claim 18, further comprising the step of identifying a sampling LED from a second of said strings.

20. The method of claim 19, further comprising the step of averaging the illumination of said sampling LEDs.

21. The method of claim 18, further comprising the step of enclosing said sampling LED in a sampling enclosure.

22. The method of claim 18, further comprising the step of forming an optical path for detecting an illumination of said sampling LED.

23. The method of claim 22, wherein said forming step comprises positioning said optical path to substantially prevent intrusion of light not emitted from said sampling LED.

24. The method of claim 22, wherein said step of forming an optical path comprises encasing said sampling LED in a light-reflective sampling enclosure.

25. The method of claim 22, wherein said step of forming an optical path comprises forming an aperture in a backplate of said LCD system.

26. A liquid crystal display illuminated using a plurality of LEDs, the display comprising:

an array of LED devices, said array comprising;

a plurality of individual LED devices connected in series to form a string;

and a plurality of said strings connected in parallel to form said array,

wherein one of said LED devices is a sampling LED;

a light sensing device in optical communication with said sampling LED;

a control circuit coupled between said light sensing device and a power source, said control circuit comprising;

a command input adapted to receive a command;

a sensing input adapted to receive a luminance signal from said light sensing device; and

a summer adapted to combine said command and said luminance signal; and

an output coupled to said power supply, wherein said control circuit generates a signal to said power supply adjusting the intensity of said array in accordance with the comparison.

27. The display of claim 26, further comprising a sampling enclosure encasing said light sensing device and said sampling LED.

28. The display of claim 26, further comprising a second of said LED devices identified as a second sampling LED.

29. The display of claim 28, wherein said first and second sampling LEDs comprise the same string.

30. The display of claim 26, wherein said first sampling LED is taken from a first string and said second sampling LED is taken from a second string.