Illumination system employing an array of microprisms

• US 5,521,725 A
• Filed: 01/03/1995
• Issued: 05/28/1996
• Est. Priority Date: 11/05/1993
• Status: Expired due to Term

• Current Assignee: Advanced Display Technologies of Texas LLC (Advanced Display Technologies)
• Original Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Inventors: Steiner, Ivan B., Zimmerman, Scott M., Beeson, Karl W.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US08/368,286
• Time in Patent Office: 511 Days
• Field of Search: 359/40, 359/42, 359/48, 359/49, 359/50, 359/69, 359/70, 359/74, 362/26, 362/27, 362/31, 362/32, 362/327, 362/330, 362/339, 362/341, 362/342, 385/36, 385/129, 385/146, 385/901
• US Class Current: 349/95
• CPC Class Codes: F21V 5/02 of prismatic shape F21V5/04 takes precedence
• CPC Class Codes: F21Y 2103/00 Elongate light sources, e.g. fluorescent tubes
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

An optical illumination system comprising a waveguide that accepts light generated by a diffuse light source and transmits the light via total internal reflection. Attached on one surface of the waveguide is a low index of refraction layer and an array of microprisms, with each microprism having an light input surface and at least one sidewall tilted at an angle from the direction normal to the surface of the waveguide such that light escapes from the waveguide, reflects off the tilted sidewalls and emerges from the microprism as a spatially-directed light source. The low index of refraction layer prevents low angle light from entering the microprisms. An array of microlenses may be positioned to accept the output of the microprisms so that the light exiting from the microlenses is a substantially collimated light source. The optical illumination system is advantageous for any application that requires a non diffuse or substantially collimated that is both energy efficient and contained in a low profile assembly.

Claims

1. An illumination assembly for providing a spatially-directed light source comprising:

(a) a light transmitting means having a first light accepting surface in close proximity to a first diffuse light source, wherein said light transmitting means transports light emanating from said first diffuse light source;

(b) an array of microprisms wherein each microprism comprises;

(i) a light input surface optically coupled to said light transmitting means;

(ii) a first pair of oppositely disposed sidewalls wherein at least one of said sidewalls forms a first tilt angle with respect to the normal of the surface of said light transmitting means; and

(iii) a second pair of oppositely disposed tilted sidewalls wherein at least one of said sidewalls forms a second tilt angle with respect to the normal of the surface of said light transmitting means; and

(c) a low index of refraction layer disposed between said light transmitting means and said light input surfaces;

wherein, a first portion of said light reflecting through said light transmitting means enters said array of microprisms through said light input surfaces, is redirected by said sidewalls and emerges from said microprisms as a spatially-directed light source and a second portion of said light reflecting through said light transmitting means is prevented from entering said light input surfaces by said low index of refraction layer.

2. The illumination assembly of claim 1 wherein said light transmitting means is a wedge-shaped waveguide and at least some of said second portion of said light is recycled within said waveguide and enters said array of microprisms through said light input surfaces, is redirected by said sidewalls and emerges from said microprisms as a spatially-directed light source.

3. The illumination assembly of claim 1 further comprising an array of microlenses, wherein the output of each microprism is directed to at least one corresponding microlens and said light transmitted through said microlenses emerges as a substantially collimated light source.

4. The illumination assembly of claim 3 wherein said microprisms and microlenses are constructed from organic polymeric material.

5. The illumination assembly of claim 1 wherein said first tilt angle is between 15 to 50 degrees to the normal of the surface of said light transmitting means.

6. The illumination assembly of claim 5 wherein said first tilt angle is between 20 and 40 degrees.

7. The illumination assembly of claim 1 wherein said second tilt angle is between 0 to 25 degrees to the normal of the surface of said light transmitting means.

8. The illumination assembly of claim 7 wherein said second tilt angle is between 2 to 20 degrees.

9. The illumination assembly of claim 1 wherein said first pair of oppositely disposed sidewalls intersect said low index of refraction layer wherein the lines of intersection are substantially parallel to said first light accepting surface and further define a width dimension and said second pair of oppositely disposed sidewalls intersect said low index of refraction layer wherein the lines of intersection are substantially perpendicular to said first light accepting surface and further define a length dimension, wherein the ratio of said length dimension to said width dimension is between about 1.2:

1 to 5;

1.

10. The illumination assembly of claim 1 wherein said light transmitting means further comprises a second light accepting surface in close proximity to a second diffuse light source, wherein said light transmitting means transports light emanating from said second diffuse light.

11. The illumination assembly of claim 3 wherein said microprisms, microlenses, and light transmitting means have an index of refraction of between about 1.45 and about 1.65.

12. The illumination assembly of claim 11 further comprising an interstitial region between said microprisms having an index of refraction less than the index of refraction of said microprisms.

13. The illumination assembly of claim 11 wherein said low index of refraction layer has an index of refraction less than that of said light transmitting means.

14. An illumination assembly for providing a spatially-directed light source comprising:

(a) a light transmitting means having a first light accepting surface in close proximity to a first diffuse light source, and a second light accepting surface in close proximity to a reflecting means for reflecting light generated by said first diffuse light source wherein said light transmitting means transports light emanating from said first diffuse light source;

(b) an array of microprisms wherein each microprism comprises;

(i) a light input surface optically coupled to said light transmitting means;

(ii) a light output surface having a surface area greater than the surface area of said light input surface;

(iii) first pair of oppositely disposed sidewalls wherein each of said sidewalls forms a first tilt angle to the normal of the surface of said light transmitting means;

(iv) a second pair of oppositely disposed tired sidewalls wherein each of said sidewalls forms a second tilt angle to the normal of the surface of said light transmitting means; and

(c) a low index of refraction layer disposed between said light transmitting means and said light input surface;

wherein, a first portion of said light reflecting through said light transmitting means enters said array of microprisms through said light input surfaces, is redirected by said sidewalls and emerges from said microprisms as a spatially-directed light source and a second portion of said light reflecting through said light transmitting means is prevented from entering said light input surfaces by said low index of refraction layer and is recycled within said waveguide by said reflecting means and enters said array of microprisms through said light input surfaces, is redirected by said sidewalls and emerges from said microprisms as a spatially-directed light source.

15. The illumination assembly of claim 14 further comprising an array of microlenses, wherein the output of each microprism is directed to at least one corresponding microlens and said light transmitted through said microlenses emerges as a substantially collimated light source.

16. The illumination assembly of claim 14 wherein said first light accepting surface and said second light accepting surface are oppositely disposed.

17. The illumination assembly of claim 14 wherein said reflecting means is a second diffuse light source and said light transmitting means transports light emanating from said second diffuse light source.

18. The illumination assembly of claim 14 wherein said first tilt angle is between 20 and 40 degrees.

19. The illumination assembly of claim 14 wherein said second tilt angle is between 0 to 25 degrees to the normal of the surface of said light transmitting means.

20. The illumination assembly of claim 19 wherein said second tilt angle is between 2 to 20 degrees.

21. The illumination assembly of claim 14 wherein said microprisms, microlenses, and light transmitting means have an index of refraction of between about 1.45 and about 1.65.

22. The illumination assembly of claim 21 further comprising an interstitial region between said microprisms having an index of refraction less than the index of refraction of said microprisms.

23. The illumination assembly of claim 21 wherein said low index of refraction layer has an index of refraction less than said light transmitting means.