Front illumination device mounted between an illuminated object and a viewer and a reflection-type liquid crystal display device incorporating same

• US 6,288,760 B1
• Filed: 03/13/1998
• Issued: 09/11/2001
• Est. Priority Date: 03/28/1997
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Sawayama, Yutaka
• Primary Examiner(s): Parker, Kenneth
• Application Number:
  US09/041,903
• Time in Patent Office: 1,278 Days
• Field of Search: 349/56, 349/64, 349/65, 349/62, 349/63, 405/46, 362/26, 362/31
• US Class Current: 349/63
• CPC Class Codes: G02B 6/0025 Diffusing sheet or layer; Prismatic sheet or layer
• 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: G02F 1/133616 Front illuminating devices

Abstract

A front-light system for mounting on the front of a reflection-type LCD, etc., which serves as auxiliary illumination when surrounding light is insufficient, is provided with a wedge-shaped light-conducting body having a light-entry surface through which light enters from a light source, and an anisotropic light-scattering plate, which scatters light projected from an interface of the light-conducting body, so that light projected toward a liquid crystal cell is projected at an angle close to perpendicular with respect to the surface of the liquid crystal cell.

Claims

1. A front illumination device comprising a light source and a light-conducting body which guides light from said light source to an object to be illuminated, said front illumination device to be used by mounting in front of said illuminated object, wherein:

said light-conducting body includes a first light-conducting body provided with a light-entry surface, through which light from said light source enters, and a second light-conducting body provided with a light exit surface, through which light exits toward said illuminated object;

said first light-conducting body guides light from said light-entry surface to said second light-conducting body;

said second light-conducting body is provided so that light exiting therefrom exits in a direction closer to a normal direction of said light exit surface of said second light-conducting body than a direction in which light, guided by said first light-conducting body from said light-entry surface toward said second light-conducting body, strikes said light exit surface of said first light-conducting body; and

said second light-conducting body is a light-scattering body, which scatters light.

2. The front illumination device set forth in claim 1, wherein:

said light-scattering body is a forward-scattering body.

3. The front illumination device set forth in claim 1, wherein:

said light-scattering body is an anisotropic scattering body, which only scatters incident light having angles of incidence within a predetermined range; and

at least part of the light projected from said first light-conducting body into said second light-conducting body has angles of incidence falling within the predetermined range.

4. The front illumination device set forth in claim 1, further comprising:

light control means, provided between said light source and said light-entry surface, which limit spread from said light source.

5. The front illumination device set forth in claim 1, wherein:

a gap between said first and second light conducting bodies is filled with a filler agent, which alleviates differences in refractive indices at optical interfaces between said first and second light conducting bodies.

6. The front illumination device set forth in claim 1, further comprising:

light-condensing means, which conveys light from said light source onto only said light-entry surface of said first light-conducting body.

7. The front illumination device set forth in claim 1, wherein:

said first light-conducting body is a polyhedron provided with a light-entry surface, through which light from said light source enters, a first light exit surface, through which light exits toward said illuminated object, and a second light exit surface opposite said first light exit surface; and

said first and second light exit surfaces being provided so that a distance therebetween grows smaller the greater a distance from said light-entry surface.

8. The front illumination device set forth in claim 7, wherein:

α

≦

90°

−

θ

_c is satisfied, where;

α

is an angle of inclination of said second light exit surface with respect to said first light exit surface; and

θ

_c is a critical angle of said second light exit surface.

9. The front illumination device set forth in claim 7, wherein:

an angle of inclination of said second light exit surface with respect to said first light exit surface is no more than 40°

.

10. A front illumination device comprising a reflection-type liquid crystal display element which has a reflective plate, in which:

the front illumination device set forth in claim 7 is provided on the front of crystal element; and

said first light-conducting body of said front illumination device is structured such that an angle of inclination of said second light exit surface with respect to said first light exit surface is no more than 10°

.

11. A reflection-type liquid crystal display device comprising a reflection-type liquid crystal element which has a reflective plate, in which:

the front Illumination device set forth in claim 1 is provided on the front of said reflection-type liquid crystal element.

12. The reflection-type liquid crystal display device set forth in claim 11, wherein:

a gap between said reflection-type liquid crystal element and said front illumination device is filled with a filler agent, which alleviates differences in refractive indices at optical interfaces between said reflection-type liquid crystal element and said front illumination device.

13. The front illumination device set forth in claim 1, wherein:

said second light-conducting body only causes light having angles of incidence within a predetermined range to exit in a direction closer to the normal direction; and

at least part of the light projected from said first light-conducting body into said second light-conducting body has angles of incidence falling within the predetermined range.

14. A front illumination device comprising a light source and a light-conducting body which guides light from said light source to an object to be illuminated, and front illumination device to be used by mounting in front of said illuminated object, wherein:

said light-conducting body includes a first light-conducting body provided with a light-entry surface, through which light from said light source enters, and a second light-conducting body provided with a light exit surface, through which light exits toward said illuminated object, said second light-conducting body being deposited on a side of said first light-conducting body opposite to said illuminated object;

said first light-conducting body guides light from said light-entry surface to said second light-conducting body;

said second light-conducting body is provided so that light exiting therefrom exits in a direction closer to a normal direction of said light exit surface than a direction in which light exits from said first light-conducting body; and

said second light-conducting body is a light-scattering body, which scatters light.

15. The front illumination device set forth in claim 14, wherein:

said light-scattering body is a forward-scattering body.

16. The front illumination device set forth in claim 14, wherein:

said light-scattering body is an anisotropic scattering body, which only scatters incident light having angles of incidence within a predetermined range; and

at least part of the light projected from said first light-conducting body into said second light-conducting body has angles of incidence falling within the predetermined range.

17. The front illumination device set forth in claim 14, further comprising:

light control means, provided between said light source and said light-entry surface, which limits spread of light from said light source.

18. The front illumination device set forth in claim 14, wherein:

a gap between said first and second light-conducting bodies is filled with a filler agent, which alleviates differences in refractive indices at optical interfaces between said first and second light-conducting bodies.

19. The front illumination device set forth in claim 14, further comprising:

light-condensing means, which converge light from said light source onto only said light-entry surface of said first light-conducting body.

20. The front illumination device set forth in claim 14, wherein:

said first light-conducting body is a polyhedron provided with a light-entry surface, through which light from said light source enters, a first light exit surface, through which light exits toward said illuminated object, and a second light exit surface opposite said first light exit surface; and

said first and second light exit surfaces are provided so that a distance therebetween grows smaller the greater a distance from said light-entry surface.

21. The front illumination device set forth in claim 20, wherein:

α

≦

90°

−

θ

_c is satisfied, where;

α

is an angle of inclination of said second light exit surface with respect to said first light exit surface; and

θ

_c is a critical angle of said second light exit surface.

22. The front illumination device set forth in claim 20, wherein:

an angle of inclination of said second light exit surface with respect to said first light exit surface is no more than 40°

.

23. A front illumination device comprising a reflection-type liquid crystal display element which has a reflective plate, in which:

the front illumination device set forth in claim 20 is provided on the front of crystal element; and

said first light-conducting body of said front illumination device is structured such that an angle of inclination of said second light exit surface with respect to said first light exit surface is no more than 10°

.

24. A reflection-type liquid crystal display device comprising a reflection-type liquid crystal element which has a reflective plate, in which:

the front Illumination device set forth in claim 14 is provided on the front of said reflection-type liquid crystal element.

25. The reflection-type liquid crystal display device set forth in claim 24, wherein:

a gap between said reflection-type liquid crystal element and said front illumination device is filled with a filler agent, which alleviates differences in refractive indices at optical interfaces between said reflection-type liquid crystal element and said front illumination device.

26. The front illumination device set forth in claim 14, wherein:

said second light-conducting body only causes light having angles of incident within a predetermined range to exit in a direction closer to the normal direction; and

at least part of the light projected from said first light-conducting body into said second light-conducting body has angles of incident falling within the predetermined range.

27. A front illumination device comprising a light source and a light-conducting body which guides light from said light source to an object to be illuminated, said front illumination device to be used by mounting in front of said illuminated object, wherein:

said light-conducting body includes a first light-conducting body provided with a light-entry surface, through which light from said light source enters, and a second light-conducting body provided with a light exit surface, through which light exits toward said illuminated object;

said first light-conducting body guides light from said light-entry surface to said second light-conducting body;

said second light-conducting body is provided so that light exiting therefrom exits in a direction closer to a normal direction of said light exit surface of said second light-conducting body than a direction in which light, guided by said first light-conducting body from said light-entry surface toward said second light-conducting body, strikes said light exit surface of said first light-conducting body; and

said second light-conducting body is a diffraction element, which diffracts light.

28. The front illumination device set forth in claim 27, wherein:

said diffracting element only diffracts light having angles of incidence within a predetermined range; and

at least part of the light projected from said first light-conducting body into said diffracting element has angles of incidence falling within the predetermined range.

29. The front illumination device set forth in claim 27, wherein:

said diffracting element is a hologram.