BACKLIGHTS HAVING SELECTED OUTPUT LIGHT FLUX DISTRIBUTIONS AND DISPLAY SYSTEMS USING SAME

• US 20110096529A1
• Filed: 02/18/2009
• Published: 04/28/2011
• Est. Priority Date: 02/22/2008
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Wheatley, John A., Watson, Philip E., Meis, Michael A., Liu, Tao, Biernath, Rolf W.
• Granted Patent: US 9,541,698 B2
• Time in Patent Office: Days
• US Class Current: 362/97.1
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type

Abstract

A backlight that includes a front reflector (120) and a back reflector (130) that form a hollow light recycling cavity including an output surface (104) is disclosed. At least a portion of the back reflector is non-parallel to the front reflector. The backlight also includes at least one semi-specular element disposed within the hollow light recycling cavity, and one or more light sources (140) disposed to emit light into the hollow light recycling cavity, where the one or more light sources are configured to emit light into the hollow light recycling cavity over a limited angular range.

Claims

1. A backlight, comprising:

a partially transmissive front reflector and a back reflector that form a hollow light recycling cavity comprising an output surface, wherein at least a first portion of the back reflector is non-parallel to the front reflector;

at least one semi-specular element disposed within the hollow light recycling cavity; and

one or more light sources disposed to emit light into the hollow light recycling cavity, wherein the one or more light sources are configured to emit light into the hollow light recycling cavity over a limited angular range.

2. The backlight of claim 1, wherein at least one of the front reflector and back reflector is non-planar.

3. The backlight of claim 1, wherein the first portion of the back reflector comprises at least 10% of a total surface area of the reflecting surface of the back reflector.

4. The backlight of claim 1, wherein a second portion of the back reflector is non-parallel to the front reflector.

5. The backlight of claim 1, wherein the back reflector is shaped to provide a desired output light flux distribution.

6. The backlight of claim 1, wherein the front reflector comprises a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector comprises a hemispherical reflectivity of unpolarized visible light of R^b_hemi, and wherein R^f_hemi*R^b_hemi is at least 0.55.

7. The backlight of claim 1, wherein a distance H measured between the front and back reflectors taken normal to the output surface varies along at least one of a length L and a width W of the hollow light recycling cavity.

8. The backlight of claim 7, wherein H is at a minimum proximate a center region of the light recycling cavity.

9. The backlight of claim 7, wherein H is at a maximum proximate an edge region of the light recycling cavity.

10. The backlight of claim 7, wherein the one or more light sources are disposed proximate an edge of the backlight, and further wherein H decreases in a direction away from the edge of the backlight.

11. The backlight of claim 1, wherein the output surface defines a transverse plane, and the one or more light sources emit light into the light recycling cavity with an average flux deviation angle relative to the transverse plane in a range from 0 to 40 degrees.

12. The backlight of claim 1, wherein the back reflector comprises a concave shape facing away from the front reflector.

13. The backlight of claim 1, wherein at least a first portion of the back reflector comprises a non-specularly reflective region.

14. The backlight of claim 1, wherein the at least one semi-specular element comprises a transport ratio greater than 15% at a 15 degree incidence angle and less than 95% at a 45 degree incidence angle.

15. The backlight of claim 1, wherein the at least one semi-specular element is disposed on a major surface of the front reflector that faces the back reflector.

16. The backlight of claim 1, wherein the at least one semi-specular element is disposed on a major surface of the back reflector that faces the front reflector.

17. The backlight of claim 1, wherein the transport ratio for the at least one semi-specular element, for light of a given incidence angle, equals (F−

B)/(F+B), where F is the amount of light scattered into forward directions upon interaction of the incident light with the element, and B is the amount of light scattered into backwards directions upon interaction of the incident light with the element.

18. The backlight of claim 1, wherein the front reflector comprises a reflectivity that generally increases with angle of incidence and a transmission that generally decreases with angle of incidence.

19. The backlight of claim 1, wherein a ratio of the luminance proximate the center region of the output surface to the luminance proximate the edge region of the output surface is at least about 1.10.

20. The backlight of claim 1, wherein the front reflector comprises a polymeric multilayer reflective polarizing film.

21. The backlight of claim 20, wherein the at least one semi-specular element comprises a layer disposed on a major surface of the polymeric multilayer reflective polarizing film facing the back reflector.

22. The backlight of claim 1, wherein the one or more light sources are disposed proximate at least one edge of the backlight.

23. The backlight of claim 22, wherein the backlight further comprises a non-planar back reflector.

24. The backlight of claim 1, wherein the backlight is a direct-lit backlight.

25. A sign comprising the backlight of claim 1.

26. A luminaire comprising the backlight of claim 1.

27. A method of forming a backlight that is operable to provide a desired output light flux distribution, comprising:

forming a hollow light recycling cavity comprising an output surface, wherein the hollow light recycling cavity further comprises a partially transmissive front reflector and a planar back reflector;

positioning one or more light sources to emit light into the light recycling cavity over a limited angular range;

selecting the desired output light flux distribution;

measuring a first output light flux distribution;

comparing the first output light flux distribution to the desired light flux distribution;

shaping the back reflector;

measuring a second output light flux distribution; and

comparing the second output light flux distribution to the desired output light flux distribution.

28. The method of claim 27, wherein shaping the back reflector comprises thermoforming the back reflector.

29. The method of claim 27, wherein shaping the back reflector comprises bending the back reflector.

30. The method of claim 27, wherein shaping the back reflector comprises stamping the back reflector.

31. A display system, comprising:

a display panel; and

a backlight disposed to provide light to the display panel, the backlight comprising;

a partially transmissive front reflector and a back reflector that form a hollow light recycling cavity comprising an output surface, wherein at least a first portion of the back reflector is non-parallel to the front reflector;

at least one semi-specular element disposed within the hollow light recycling cavity; and

one or more light sources disposed to emit light into the hollow light recycling cavity, wherein the one or more light sources are configured to emit light into the hollow light recycling cavity over a limited angular range.