Light guide and liquid crystal display device using it

• US 5,719,649 A
• Filed: 06/06/1995
• Issued: 02/17/1998
• Est. Priority Date: 06/08/1994
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Ide, Naoto, Shono, Yasuo, Higuchi, Yoshinori, Suzuki, Yasoji
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/466,796
• Time in Patent Office: 987 Days
• Field of Search: 349/62, 349/64, 349/65, 362/31
• US Class Current: 349/65
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects

Abstract

On a light exit surface which is the first principal plane of a light guide, multiple projections are fabricated in specific rows. These projections have light exit surfaces and continuous multiple slopes, and are fabricated from optically identical materials having the same refractive index as the substrate of the light guide. The slope farthest from the light entry edge surface is formed as a light exit surface, i.e., a surface which breaks the conditions for the total reflection of the incident light. On the other hand, the slope nearest the light entry edge surface which is the total reflection surface is formed such that the incident light is totally reflected.

Claims

1. A light guide having at least one side of a flat substrate as a light entry surface, and a first principal plane of the substrate intersecting the light entry surface as a light exit surface, wherein the improvement comprises:

multiple projections placed within the light exit surface fabricated from materials optically identical with the substrate, each of the projections having a light exit slope farthest among slopes of the projection from the light entry surface, the light exit slope projecting the incident light, and slopes other than the light exit slope fulfilling the conditions for total reflection of incident light.

2. The light guide of claim 1 wherein, from among the light exit main surfaces, all surfaces other than the light exit surface of the projection fulfill the conditions for total reflection of incident light.

3. The light guide of claim 1 wherein all surfaces other than the light exit principal plane fulfill the conditions for total reflection of incident light.

4. The light guide of claim 1 wherein the multiple projections are placed such that the further they are from the light entry surface, the bigger volume they are.

5. The light guide of claim 1 wherein the multiple projections are of identical volume and are fabricated such that the further they are from the light entry surface, the higher density they occupy on the light exit surface.

6. A liquid crystal display device having a liquid crystal panel wherein a liquid crystal layer is held between two parallel boards, and at the back of the panel is installed a light guide having at least one side of a flat substrate as a light entry surface, and a first principal plane of the substrate intersecting the light entry surface as a light exit surface, wherein the improvement comprises:

multiple projections placed within the light exit surface fabricated from materials optically identical with the substrate, each of the projections having a light exit slope farthest among slopes of the projection from the light entry surface, the light exit slope projecting the incident light, and slopes other than the light exit slope fulfilling the conditions for total reflection of incident light; and

an optical element that controls the optical path of the emergent light from the light guide interposed between the liquid crystal panel and the light exit surface of the light guide.

7. The liquid crystal display device of claim 6 wherein the pitch of the projection of the light guide is smaller than the pitch of the pixel comprising the liquid crystal panel.

8. The liquid crystal display device of claim 6 wherein the optical element is a prism sheet.

9. The liquid crystal display device of claim 8 wherein the pitch of the prisms comprising the prism sheet is smaller than a pixel comprising the liquid crystal panel.

10. The liquid crystal display device of claim 8 wherein the pitch of the prism comprising the prism sheet is smaller than the pixel comprising the liquid crystal panel and larger than the pitch of the projections of the light guide.

11. The liquid crystal display device of claim 6 wherein the optical element can switch over between a system which transmits emergent light from the light guide and a system which scatters the certain emergent light.

12. The liquid crystal display device of claim 11 wherein the optical element is a polymer dispersing liquid crystal cell.

13. The liquid crystal display device of claim 11 wherein one board of the high polymer liquid crystal has polarizing ability.

14. The liquid crystal display device of claim 6, wherein the optical element that controls the optical path of the emergent light from the light guide is placed on the front face of one of two parallel boards, the front face being seen from the viewing side of said liquid crystal panel.

15. The liquid crystal display device of claim 6, wherein a polarizing element is intervened between the light exit principal plane of the light guide and the light source.

16. A panel light source device comprising a tube light source and a light guide which propagates light from said light tube source, wherein:

said light guide includes multiple projections which are installed on a first principal plane of said light guide and each of the projections has a light reflecting surface and light exiting surface and includes a first reflecting plane and a second reflecting plane on a second principal plane facing the first principal plane, the first and second principal planes intersecting each other at a predetermined angle.

17. The panel light source of claim 16, wherein the first reflecting plane is faced with the projections and the second reflecting plane is faced with the plane among the neighboring projections.

18. A display device comprising a display panel which includes an display region made up of multiple display pixels, and a panel light source which includes a tube light source and a light guide to propagate light from the tube light source, wherein said light guide includes multiple projections on a first principal plane of said light guide, each of which has a light reflecting surface and light exiting surface and includes a first reflecting plane and a second reflecting plane on a second principal plane facing the first principal plane, the first and second principal planes intersecting with each other at a predetermined angle.

19. A panel light source which includes a tube light source and a light guide having multiple projections on a first projection plane, each of the projections having a light reflective slope and a light exiting plane:

wherein said tube light source is stored within the thickness of the light guide, the light guide further including a storage section having a light entry surface fabricated within said thickness to guide light from said tube light source into the light guide.

20. A display device comprising:

a display panel which includes an display region made up of multiple display pixels; and

a panel light source which includes a tube light source exposing light onto said display panel and a light guide having multiple projections on the first principal plane, each of the projections having a light reflective slope and a light exiting plane, and optionally releasing light from said tube light source,

wherein said tube light source is stored within the thickness of the light guide, the light guide further including a storage section having a light entry surface fabricated within said thickness to guide said light from said tube light source into the light guide.

21. The display device of claim 20, wherein the tube light source is installed to be adapted within said effective display area of said display panel.

22. A display device comprising:

a display panel having a display region made of multiple display pixels;

a driving circuitry that drives said display panel;

a tube light source;

a light guide that includes a light entry surface which is installed near said tube light source and in which light from said tube light source enters;

multiple projections on a first principal plane of the light guide, each of the projections having a light reflective slope and a light exiting plane, wherein said light guide includes a region thinner than the light guide thickness of said light entry surface; and

said driving circuitry is installed near said region.

23. A display device wherein each of the projections described in claim 22 has a triangular cross section and includes a first exit surface from which said light source light from said tube light source propagating inside said light guide is released outside said light guide and a first reflection surface which either guides to the first exit surface of said light source, or reflects inside said light guide said light source light from said tube light source propagating inside said light guide.

24. A display device wherein said display panel described in claim 22 and said driving circuitry are electrically connected through a flexible wiring circuit board.

25. A display device wherein said flexible wiring circuit board in claim 24 includes driving ICs.

26. A display device wherein driving ICs are mounted the display panel described in claim 24.

27. A light guide comprising:

a light entry surface;

a first principal plane intersecting the light entry surface; and

at least one projection on the first principal plane optically identical with the light guide, the projection having a light emitting surface disposed farthest from the light entry surface and a totally reflective surface disposed closest to the light entry surface.