LCD backlight using two-dimensional array LEDs

• US 20050073495A1
• Filed: 10/03/2003
• Published: 04/07/2005
• Est. Priority Date: 10/03/2003
• Status: Active Grant

• Current Assignee: Philips North America LLC (Koninklijke Philips N.V.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Harbers, Gerard, Collins, William D. III
• Granted Patent: US 7,052,152 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133609 including means for improving the color mixing, e.g. white
• CPC Class Codes: G02F 1/133614 using photoluminescence, e.g. phosphors illuminated by UV or blue light
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

One embodiment of the invention provides a backlight for an LCD display. The backlight uses a two-dimensional array of single color or white LEDs and a diffusing or phosphor coated cover plate. Various electrical connections of the LEDs and various phosphor color-conversion techniques are described.

Claims

1. A display device comprising:

a housing comprising reflective surfaces and a top opening through which light is emitted for backlighting a liquid crystal display (LCD) panel;

an array of substantially identical light emitting diodes (LEDs) supported on a reflective bottom surface in the housing, each LED emitting light through top and side portions of the LED, the LEDs being separated from one another by a distance greater that the width of a single LED; and

a diffuser above the LEDs for providing diffused light to an LCD panel.

2. The device of claim 1 further comprising an LCD panel over the diffuser.

3. The device of claim 1 wherein the housing has a height, and wherein a ratio of the height to the pitch of the LEDs is between approximately 0.3 to 1.2.

4. The device of claim 1 wherein a pitch of the LEDs is greater than 20 mm.

5. The device of claim 1 wherein each of the LEDs output light having red, green, and blue components.

6. The device of claim 1 wherein the LEDs comprise only blue LEDs.

7. The device of claim 1 wherein the LEDs comprise only UV or near-UV LEDs.

8. The device of claim 1 further comprising phosphor over the LEDs to convert light output by the LEDs into at least red and green light.

9. The device of claim 1 further comprising phosphor over the LEDs to convert light output by the LEDs into red, green, and blue light.

10. The device of claim 1 further comprising a phosphor layer beneath the diffuser.

11. The device of claim 1 further comprising a phosphor layer deposited on the diffuser.

12. The device of claim 1 further comprising phosphor surrounding top and side portions of each LED for color-converting light emitted by the LEDs.

13. The device of claim 1 wherein the diffuser comprises a phosphor, and the phosphor performs a diffusing function.

14. The device of claim 1 wherein a number of LEDs are connected in series, a total voltage drop across the serially connected LEDs approximately equaling a publicly supplied standard voltage.

15. The device of claim 1 wherein a number of LEDs are connected in series, a total voltage drop across the serially connected LEDs approximately equaling a publicly supplied standard AC supply voltage that has been rectified and filtered to be DC.

16. The device of claim 1 wherein a number of LEDs are connected in series, a total voltage drop across the serially connected LEDs approximately equaling a publicly supplied standard AC supply voltage that has been rectified and filtered to be DC, wherein LEDs in the array are connected to perform a rectification of the AC supply voltage.

17. The device of claim 1 wherein the LEDs are arranged in a rectangular grid.

18. The device of claim 1 wherein the LEDs are arranged in a hexagonal grid.

19. The device of claim 1 wherein the LEDs are connected in groups of series-connected LEDs.

20. The device of claim 1 wherein the LEDs are connected such that a light output of individual LEDs or a portion of the LED array can be independently controlled to adjust the light output to improve uniformity of the light applied to the LCD panel.

21. The device of claim 1 further comprising a plurality of light sensors in the housing for detecting an intensity of light, the sensors being coupled to a controller for controlling a brightness of LEDs associated with a sensor.

22. The device of claim 1 further comprising a plurality of light sensors in the housing for detecting an intensity of light, the sensors being coupled to a controller for controlling a gray scale level of pixels in the LCD panel.

23. The device of claim 1 further comprising:

a first type of phosphor above the LEDs for converting light emitted by the LEDs to a first color; and

a second type of phosphor on the bottom surface in the housing for converting light emitted by the LEDs to a second color.

24. The device of claim 23 wherein a combination of the light emitted by the LEDs, the first type of phosphor, and the second type of phosphor produces a substantially white light for backlighting the LCD panel.

25. The device of claim 23 wherein the first type of phosphor is in the form of dots.

26. The device of claim 25 wherein the dots are deposited on the diffuser.

27. The device of claim 23 wherein the first type of phosphor converts blue light to one of red light or green light, and the second type of phosphor converts blue light to the other of red light and green light.

28. The device of claim 1 further comprising a phosphor layer for converting light from the LEDs to one or more other colors, the phosphor layer being formed on the LCD panel.

29. The device of claim 28 wherein the phosphor layer is formed on a thin film transistor transparent layer in the LCD panel

30. The device of claim 1 wherein the reflective bottom surface in the housing comprises a bottom surface forming the housing.

31. A method for constructing a display comprising:

providing a housing comprising reflective surfaces and a top opening through which light is emitted for backlighting a liquid crystal display (LCD) panel;

providing an array of substantially identical light emitting diodes (LEDs) supported on a reflective bottom surface in the housing, each LED emitting light through top and side portions of the LED, the LEDs being separated from one another by a distance greater that the width of a single LED; and

providing a diffuser above the LEDs for providing diffused light to an LCD panel.

32. The method of claim 31 further comprising an LCD panel over the diffuser.