LED light engine for backlighting a liquid crystal display

• US 20060104090A1
• Filed: 11/12/2004
• Published: 05/18/2006
• Est. Priority Date: 11/12/2004
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Holmes, Jonathan Frank, Lengyel, John Michael
• Granted Patent: US 7,220,040 B2
• Time in Patent Office: Days
• US Class Current: 362/612
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

An edge-lit backlighting system for liquid crystal displays employs a number of light strips in the form of thin, light weight sections of a thermally conductive substrate each of which mounts a plurality of light engines having an array of densely packed, primary color light emitting diodes, which, when collectively illuminated, produce a white light of desired reference white chromaticity.

Claims

1. A light-strip for use in an edge-lit backlighting system employed with a liquid crystal display, comprising:

a thermally conductive substrate formed in an elongated strip;

a plurality of light engines mounted at spaced intervals along said elongated strip, each of said light engines including a plurality of primary color light emitting diodes, said light emitting diodes being selected so that when collectively illuminated a white light of desired reference white chromaticity is produced.

2. The light strip of claim 1 in which said thermally conductive substrate is a printed wiring board.

3. The light strip of claim 1 in which said elongated strip is formed with lines of weakness at intervals therealong in between said light engines, said elongated strip being breakable at each of said lines of weakness to allow for the formation of a shortened strip of desired length.

4. The light strip of claim 1 in which said light emitting diodes are arranged in an array on said elongated strip of at least two parallel legs, said light emitting diodes in each leg being connected in series.

5. The light strip of claim 4 in which said elongated strip has two parallel legs of light emitting diodes, each of said legs including six light emitting diodes connected in series.

6. The light strip of claim 5 in which said six light emitting diodes in each parallel leg includes three green, two red and one blue, said six light emitting diodes when collectively illuminated producing a desired reference white chromaticity.

7. The light strip of claim 1 in which said light emitting diodes of each light engine are arranged in three discrete arrays, one of said arrays having red light emitting diodes, another having green light emitting diodes and the third having blue light emitting diodes.

8. The light strip of claim 7 in which said light emitting diodes within at least one of said arrays are arranged in parallel legs with said light emitting diodes in each leg being connected in series.

9. The light strip of claim 7 in which a forward voltage and current is applied to each array of light emitting diodes in an independent manner to permit variation of the magnitude of light for each color primary in each array.

10. A light strip for use in an edge-lit backlighting system employed with a liquid crystal display, comprising:

a thermally conductive substrate formed in an elongated strip;

a plurality of light engines mounted at spaced intervals along said elongated strip, each of said light engines including a plurality of primary color light emitting diodes arranged in an array of at least two parallel legs, said light emitting diodes in each leg being connected in series, said light emitting diodes being selected so that when collectively illuminated a white light of desired reference white chromaticity is produced.

11. The light strip of claim 10 in which said elongated strip has two parallel legs of light emitting diodes, each of said legs including six light emitting diodes connected in series.

12. The light strip of claim 11 in which said six light emitting diodes in each parallel leg includes three green, two red and one blue, said six light emitting diodes when collectively illuminated producing a desired reference white chromaticity.

13. The light strip of claim 10 in which said thermally conductive substrate is a printed wiring board.

14. The light strip of claim 10 in which said elongated strip is formed with lines of weakness at intervals therealong in between said light engines, said elongated strip being breakable at each of said lines of weakness to allow for the formation of a shortened strip of desired length.

15. A light strip for use in an edge-lit backlighting system employed with a liquid crystal display, comprising:

a thermally conductive substrate formed in an elongated strip;

a plurality of light engines mounted at spaced intervals along said elongated strip, each of said light engines including a plurality of primary color light emitting diodes arranged in three discrete arrays, a first one of said arrays having red light emitting diodes, a second one of said arrays having green light emitting diodes and a third one of said arrays having blue light emitting diodes, a voltage being applied to each of said arrays which is separately controlled to permit independent variation of the intensity of red, blue or green light produced by respective arrays, said intensity of red, green and blue light from respective arrays being selected so that when collectively illuminated a white light of desired reference white chromaticity is produced.

16. The light strip of claim 15 in which said light emitting diodes within at least one of said arrays are arranged in parallel legs with said light emitting diodes in each leg being connected in series.

17. The light strip of claim 15 in which said thermally conductive substrate is a printed wiring board.

18. The light strip of claim 15 in which said elongated strip is formed with lines of weakness at intervals therealong in between said light engines, said elongated strip being breakable at each of said lines of weakness to allow for the formation of a shortened strip of desired length.

19. An edge-lit backlighting system for use with a liquid crystal display, comprising:

a heat exchanger;

at least one light strip including a plurality of light engines mounted at spaced intervals therealong, each of said light engines including a plurality of primary color light emitting diodes, said light emitting diodes being selected so that when collectively illuminated a white light of desired reference white chromaticity is produced;

a light reflective sheet coupled to said at least one light strip, said light reflective sheet and said at least one light strip being mounted to said heat exchanger;

a light guide mounted in position to receive said white light produced by said at least one light strip; and

at least one enhancement film overlying said light guide.

20. The system of claim 19 in which said at least one light strip includes a thermally conductive substrate formed in an elongated strip, said plurality of light engines being coupled to said elongated strip.

21. The system of claim 20 in which said thermally conductive substrate is a printed wiring board, said printed wiring board being formed with at least one metal heat spreader and a number of thermally conductive via in thermal communication with each of said light engines mounted thereto.

22. The system of claim 21 in which said printed wiring board is formed with lines of weakness at intervals therealong in between said light engines, said printed wiring board being breakable at each of said lines of weakness to allow for the formation of a shortened strip of desired length.

23. The system of claim 21 further including a layer of thermally conductive material connected between said printed wiring board and said heat exchanger, said layer being flexible to form a seal at said printed wiring board and at said heat exchanger.

24. The system of claim 19 in which said light emitting diodes on each light engine are collectively disposed within a protective casing which protrudes from the surface of said light engine.

25. The system of claim 24 in which said protective casing is a clear section of low temperature glass ceramic material.

26. The system of claim 24 in which said light reflective sheet has an upturned, peripheral edge formed with a plurality of spaced apertures, each of said apertures receiving one of said protective casings of a light engine to permit the transmission of white light to said light guide while said space along said at least one light strip between adjacent light engines is covered by said reflective sheet.