LED-based white-light backlighting for electronic displays

• US 20030230991A1
• Filed: 06/17/2002
• Published: 12/18/2003
• Est. Priority Date: 06/17/2002
• Status: Active Grant

• 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, Muthu, Subramanian, Gaines, James, Schuurmans, Frank J.
• Granted Patent: US 6,753,661 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• 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: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/28 using temperature feedback

Abstract

Apparatus and method for backlighting an electronic display with LEDs to control luminosity, radiometric power, and color levels by means of feedback control through a microprocessor, thereby maintaining white backlight at substantially constant levels, which can be chosen by an operator.

Claims

1. Apparatus for backlighting an electronic display with white light, which comprises:

a plurality of light-emitting diodes (LEDs), each of said LEDs effective for emitting light of a single color;

at least one light source comprised of at least three of said LEDs arranged in a combination that produces white light;

a light guide effective for illuminating said display with said white light;

circuitry effective for maintaining said white light at a substantially constant level of color and luminosity by controlling said at least one light source; and

said circuitry being controlled either automatically or manually.

2. Apparatus as in claim 1, wherein said circuitry includes a microprocessor effective for controlling current flowing to said LEDs.

3. Apparatus as in claim 2, wherein said circuitry includes at least one set of photo diodes effective for measuring luminosity of said light guide and sending a value thereof to said microprocessor.

4. Apparatus as in claim 2, wherein said circuitry includes at least one set of photo diodes effective for measuring radiometric power level in said light guide and sending a value thereof to said microprocessor.

5. Apparatus as in claim 2, wherein said circuitry includes at least one set of photo diodes effective for measuring color values of said white light in said light guide and sending said values to said microprocessor.

6. Apparatus as in claim 2, wherein said plurality of LEDs are embedded in at least one heat sink, said heat sink being fitted with at least one sensor effective for measuring a temperature of said LEDs and forwarding said temperature to said microprocessor.

7. Apparatus as in claim 6, wherein said sensor and at least one set of photo diodes effective for measuring luminosity of said light guide send outputs simultaneously to said microprocessor.

8. Apparatus as in claim 6, wherein said sensor and at least one set of photo diodes effective for measuring radiometric power level in said light guide send outputs simultaneously to said microprocessor.

9. Apparatus as in claim 6, wherein said sensor and at least one set of photo diodes effective for measuring tristimulus values of said white light in said light guide send outputs simultaneously to said microprocessor.

10. Apparatus as in claim 1, wherein said at least one set of photo diodes contains three diodes placed an effective distance from each other in a row along an end of said light guide opposite a single at least one light source, a middle member of said set being placed substantially at the center of said end.

11. Apparatus as in claim 1, wherein said at least one set of photo diodes contains three diodes placed an effective distance from each other in a horizontal row substantially at the middle of said light guide, a middle member of said set being placed substantially at the center of said light guide and said at least one light source being a pair of light sources at respective ends of said light guide.

12. A method for backlighting an electronic display with white light, which comprises the steps of:

driving a plurality of LEDs, each of said LEDs emitting light of a single color;

combining light emitted from at least three of said LEDs to form white light;

illuminating said display with said white light; and

controlling the color and brightness of said white light by means of feedback circuitry.

13. The method of claim 12, wherein said step of controlling includes a further step of sensing the temperature of said LEDs.

14. The method of claim 12, wherein said step of controlling includes a further step of sensing the radiometric power level of said white light by means of at least one set of photo diodes.

15. The method of claim 12, wherein said step of controlling includes a further step of sensing the luminosity of said white light by means of at least one set of photo diodes.

16. The method of claim 12, wherein said step of controlling includes a further step of sensing the color values of said white light by means of at least one set of photo diodes.

17. The method of claim 12, wherein said step of controlling includes a further step of combining the sensed tristimulus values of said white light with the sensed temperature of said LEDs.

18. The method of claim 12, wherein said step of controlling includes a step of combining the sensed luminosity of said white light with the sensed temperature of said LEDs.

19. The method of claim 12, wherein said step of controlling includes a further step of combining the sensed radiometric power level of said white light with the sensed temperature of said LEDs.

20. Apparatus for backlighting an electronic display with white light, which comprises:

means for driving a plurality of LEDs, each of said LEDs emitting light of a single color;

means for combining light emitted from at least three of said LEDs to form white light;

means for illuminating said display with said white light;

means for controlling the color and brightness of said white light by feedback circuitry; and

said means for controlling being subject to an operator'"'"'s direction.