THIN HOLLOW BACKLIGHTS WITH BENEFICIAL DESIGN CHARACTERISTICS

• US 20100156953A1
• Filed: 05/19/2008
• Published: 06/24/2010
• Est. Priority Date: 05/20/2007
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hebrink, Timothy J., Wheatley, John A., Freier, David G., Weber, Michael F., Ouderkirk, Andrew J., Biernath, Rolf W., Nevitt, Timothy J., Derks, Kristopher J., Hoyle, Charles D.
• Granted Patent: US 8,523,419 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: F21V 7/04 Optical design
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A backlight unit (10) has a hollow cavity (16) instead of employing a light guide. One or more light sources (24a-c), such as LEDs, are arranged to emit light into the cavity, which is formed by a front (12) and a back reflector (14). The backlight is typically of the edge-lit type. The backlight can have a large area, is thin and consists of fewer components than conventional devices. Its design permits light recycling. The unit emits light of a predefined polarisation and can be arranged to have desired horizontal/vertical viewing angle properties. Light is uniformly distributed within the guide and the light output (20b, 2Od) is substantially collimated. Such backlights occupy a specific region in a parameter space defined by two parameters: first, the ratio of the output emission area to the total source emission area should lie in the range 0.0001 to 0.1; and second, the ratio of the SEP to the height of the cavity (H) should be in the range 3 to 10, where the SEP is an average plan view source separation, a special measure of the average spacing of light sources in the plane of the unit. There is also a discussion on the required number of light sources N, their arrangement near the periphery of the cavity, as well as the shape and size of the output emission area. A required minimum brightness uniformity (VESA) value to be maintained, when a subset of Madjacent sources is switched off (where M is at least 0.1 N or M>2 or both), is also disclosed. The backlight can be used for a display or for general lighting purposes.

Claims

1. An edge-lit backlight, comprising:

a front and back reflector forming a hollow light recycling cavity having a cavity depth H and an output region of area Aout; and

one or more light sources disposed proximate a periphery of the backlight to emit light into the light recycling cavity, the light sources having an average plan view source separation of SEP and collectively having an active emitting area Aemit;

wherein a first parameter equals Aemit/Aout;

wherein a second parameter equals SEP/H; and

wherein the backlight is characterized by the first parameter being in a range from 0.0001 to 0.1, and by the second parameter being in a range from 3 to 10.

2. The backlight of claim 1, wherein the one or more light sources comprise one or more LEDs.

3. The backlight of claim 1, wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^f_hemi*R^b_hemi is at least 0.70.

4. The backlight of claim 3, wherein R^f_nemi*R^b_hemi is at least 0.80.

5. The backlight of claim 1, wherein the backlight exhibits a VESA 9 uniformity value of at least 50% over the output region.

6. The backlight of claim 5, wherein the backlight exhibits a VESA 9 uniformity value of at least 60%.

7. The backlight of claim 6, wherein the backlight exhibits a VESA 9 uniformity value of at least 70%.

8. The backlight of claim 6, wherein the backlight exhibits a VESA 9 uniformity value of at least 80%.

9. The backlight of claim 1, wherein the output region is generally rectangular and has a diagonal measure of at least 12 inches.

10. The backlight of claim 9, wherein the diagonal measure is at least 23 inches.

11. The backlight of claim 10, wherein the diagonal measure is at least 40 inches.

12. An edge-lit backlight, comprising:

a front and back reflector forming a hollow light recycling cavity having a cavity depth H and an output region of area Aout; and

a number N of one or more light sources disposed proximate a periphery of the light recycling cavity and emitting light into the light recycling cavity;

wherein the output region is generally rectangular in shape and has a diagonal measure of at least 30 inches.

13. The backlight of claim 12, wherein the one or more light sources comprise one or more LEDs.

14. The backlight of claim 12, wherein the output region exhibits a VESA 9 uniformity value of at least 50%.

15. The backlight of claim 14, wherein the output region exhibits a VESA 9 uniformity value of at least 70%.

16. The backlight of claim 12, wherein the one or more light sources have an average plan view source separation of SEP and collectively have an active emitting area Aemit;

wherein a first parameter equals Aemit/Aout;

wherein a second parameter equals SEP/H; and

wherein the backlight is characterized by the first parameter being in a range from 0.0001 to 0.1, and by the second parameter being in a range from 3 to 10.

17. A backlight, comprising:

a front and back reflector forming a hollow light recycling cavity having an output region; and

a number N of light sources disposed to emit light into the light recycling cavity, the N light sources including a subset of M light sources that are adjacent to each other,

where M is at least 10% of N, or is at least 2, or both;

wherein the backlight exhibits a VESA brightness uniformity value over its output region of at least 50% both when all N light sources are energized and when all of the M light sources are selectively turned off.

18. The backlight of claim 17, wherein the recycling cavity has a depth H;

wherein the output region has an area Aout;

wherein the N light sources have an average plan view source separation of SEP and collectively have an active emitting area Aemit;

wherein a first parameter equals Aemit/Aout;

wherein a second parameter equals SEP/H; and

wherein the backlight is characterized by the first parameter being in a range from 0.0001 to 0.1, and by the second parameter being in a range from 3 to 10.

19. The backlight of claim 17, wherein the front and back reflectors are each substantially spatially uniform.

20. The backlight of claim 17, wherein the N light sources are predominantly disposed proximate a periphery of the output region to provide an edge-lit backlight.

21. The backlight of claim 17, wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^f_hemi*R^b_hemi is at least 0.70.