Multi-colored LED array with improved brightness profile and color uniformity

• US 20050001537A1
• Filed: 05/07/2004
• Published: 01/06/2005
• Est. Priority Date: 03/28/2003
• Status: Active Grant

• Current Assignee: Philips Lighting North America Corporation (Signify N.V.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: West, Robert S., Martynov, Yourii, Pfeffer, Nicola, Schrama, Charles, Konijn, Huub, Kuppens, Simon
• Granted Patent: US 7,320,531 B2
• Time in Patent Office: Days
• US Class Current: 313/500
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133611 including means for improving the brightness uniformity
• CPC Class Codes: G02F 1/133613 characterized by the sequence of light sources
• CPC Class Codes: G02F 2201/52 RGB geometrical arrangements
• CPC Class Codes: H01L 33/58 Optical field-shaping elements
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

A backlight uses an array of red, green, and blue LEDs in a mixing chamber. The mixing chamber has reflecting surfaces and a top opening for illuminating LCD layers. A desired brightness profile and better color uniformity are obtained by using techniques including arranging the LEDs in certain sequences and patterns, providing a specular ring at the base of each LED, attenuating the brightness of the LEDs at the edges, and using widely separated diffusers in the mixing chamber. The arrangement, selection, and control of the multicolored LEDs may be tailored to achieve any desired white point specified by the display manufacturer.

Claims

1. A light emitting device comprising:

a light mixing cavity having reflective side walls and a reflective bottom surface;

a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface;

a first diffuser substantially parallel with the bottom surface and located above the LEDs a first distance; and

a second diffuser substantially parallel with the first diffuser and located above the LEDs a second distance, wherein the first distance is between approximately 25%-75% of the second distance.

2. The device of claim 1 wherein each LED in the plurality of LED comprises an LED semiconductor chip with a side-emitting lens.

3. The device of claim 1 further comprising a substantially circular reflector over each LED to reflect light back toward the bottom surface of the mixing cavity.

4. The device of claim 1 further comprising a brightness enhancement film above the second diffuser.

5. The device of claim 1 further comprising one or more liquid crystal display layers above the second diffuser.

6. The device of claim 1 wherein the first distance is between approximately 25%-33% of the second distance.

7. The device of claim 1 wherein the first distance is between approximately 33%-50% of the second distance.

8. The device of claim 1 wherein the first distance is between approximately 50%-75% of the second distance.

9. A method of backlighting a display comprising:

energizing a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface of a light mixing cavity having reflective side walls and a reflective bottom surface, each LED including a side emitting lens to cause a majority of light emitted by each LED to be substantially parallel to the bottom surface;

reflecting light emitted by the LEDs generally normal to the bottom surface so that the light emitted by the LEDs generally normal to the bottom surface is mixed in the mixing cavity;

diffusing light by a first diffuser located substantially parallel with the bottom surface and located above the LEDs a first distance; and

diffusing light by a second diffuser located substantially parallel with the first diffuser and located above the LEDs a second distance, wherein the first distance is between approximately 25%-75% of the second distance.

10. The method of claim 9 wherein the first distance is between approximately 25%-33% of the second distance.

11. The method of claim 9 wherein the first distance is between approximately 33%-50% of the second distance.

12. The method of claim 9 wherein the first distance is between approximately 50%-75% of the second distance.

13. A light emitting device comprising:

a light mixing cavity having reflective walls and a reflective bottom surface; and

a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface in parallel rows, each row having two ends,

one or more LEDs at the ends of the rows having a reduced brightness compared to the same color LEDs toward a middle of the rows to improve color uniformity.

14. The device of claim 13 wherein the one or more LEDs at the ends of the rows having a reduced brightness comprise any of the last 1-5 LEDs at the ends of the rows.

15. The device of claim 13 wherein the one or more LEDs at the ends of the rows having a reduced brightness comprise one or more LEDs having a brightness of less than 75% of the brightness of a same color LED toward the middle of a row.

16. The device of claim 13 further comprising a shunting device coupled to the one or more LEDs at the ends of the rows for reducing the brightness of the one or more LEDs.

17. The device of claim 13 wherein the one or more LEDs at the ends of the rows are LEDs that have been tested to determine their relative brightness levels and have been determined to have a low relative brightness level.

18. The device of claim 13 further comprising LED driver circuitry, the driver circuitry driving the one or more LEDs at the ends of the rows with a current that is less than the current driving the same color LEDs toward the middle of the rows.

19. The device of claim 13 further comprising one or more liquid crystal display layers above the LEDs.

20. A method of backlighting a display comprising:

energizing a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near a bottom surface of a light mixing cavity having reflective walls and a reflective bottom surface, the LEDs being arranged in parallel rows, each row having two ends; and

causing one or more LEDs at the ends of the rows to have a reduced brightness compared to the same color LEDs toward a middle of the rows to improve color uniformity.

21. A light emitting device comprising:

a light mixing cavity having reflective walls and a reflective bottom surface;

a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface in parallel rows, each row having two ends; and

one or more LEDs located near the ends of two adjacent rows to form substantially rectangular arrangements of LEDs for improving color uniformity.

22. The device of claim 21 wherein the one or more LEDs comprise a plurality of LEDs arranged in a line perpendicular to the rows.

23. The device of claim 22 wherein the plurality of LEDs comprises 2-4 LEDs arranged in a line perpendicular to the rows.

24. A light emitting device comprising:

a light mixing cavity having reflective walls and a reflective bottom surface; and

substantially circular clusters of red, green, and blue light emitting diodes (LEDs) arranged on the bottom surface.

25. The device of claim 24 wherein at least some of the circular clusters include a center LED.

26. The device of claim 24 wherein each circular cluster has 7-9 LEDs.

27. A light emitting device comprising:

a light mixing cavity having reflective side walls and a reflective bottom surface;

a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface; and

a specular ring surrounding individual LEDs for reducing Lambertian reflections off the bottom surface in the vicinity of the LEDs.

28. The device of claim 27 wherein each LED in the plurality of LEDs comprises an LED semiconductor chip with a side-emitting lens to cause a majority of light emitted by each LED to be substantially parallel to the bottom surface.

29. The device of claim 27 wherein the mixing cavity further comprises at least one diffuser above the LEDs.

30. A light emitting device comprising:

a light mixing cavity having reflective walls and a reflective bottom surface; and

a plurality of red, green, and blue light emitting diodes (LEDs) arranged on or near the bottom surface in a plurality of parallel rows, the red, green, and blue LEDs being arranged in each row to have a repeating sequence of one of GRBG, GRBRG, RGBGR, GRBBRG, RGBBGR, GRBGGBRG; and

GRBBRGGRB.

31. The device of claim 30 wherein the repeating sequence is GRBRG.

32. The device of claim 30 wherein the sequence in adjacent rows is reversed.