Surface light source device and liquid crystal display device using the same

• US 5,914,760 A
• Filed: 06/18/1997
• Issued: 06/22/1999
• Est. Priority Date: 06/21/1996
• Status: Expired due to Term

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Daiku, Yasuhiro
• Primary Examiner(s): Bovernick, Rodney
• Assistant Examiner(s): CHOWDHURY, TARIFUR RASHID
• Application Number:
  US08/878,412
• Time in Patent Office: 734 Days
• Field of Search: 349/1, 349/62, 349/65, 349/95, 361/681, 362/26, 362/31, 362/331, 362/339
• US Class Current: 349/65
• CPC Class Codes: G02B 3/005 arranged along a single direction only, e.g. lenticular sheets G02B3/0043 takes precedence
• CPC Class Codes: G02B 3/0056 arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085
• CPC Class Codes: G02B 3/0075 characterized by non-optical structures, e.g. having integrated holding or alignment means
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 5/045 Prism arrays
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/0018 Redirecting means on the surface of the light guide
• CPC Class Codes: G02B 6/0048 with stepwise taper
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer

Abstract

A surface light source device includes a light source, a light guide plate for guiding light from the light source to one surface, and a light-condensing member for outputting exit light from the light guide plate in a predetermined direction. The one surface of the light guide plate is a stepped surface whose thickness decreases step by step at a predetermined pitch from one end, at which the light source is arranged, to the other. The light-condensing member is located to face the light guide plate and includes a plurality of prisms for refracting exit light from the light guide plate toward the direction of a normal to the light guide plate, and a plurality of lenses for condensing and outputting light in a direction within a predetermined range of angles.

Claims

1. A surface light source device comprising:

a light source;

a light guide plate, formed from one block of an optically homogeneous transparent material, at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range.

2. A device according to claim 1, wherein said light guide plate has a reflection surface for reflecting light incident from one end, and the stepped surface has raised surfaces for outputting light guided by said light guide plate.

3. A device according to claim 2, wherein said light-condensing member comprises a prism member having an array of a plurality of prisms which refract exit light from the raised surfaces of the stepped surface in a direction in which an angle with respect to a normal to an envelope plane of the stepped surface decreases, and a condenser lens unit arranged in a light exit direction of said light-condensing member and having an array of a plurality of condenser lenses which condense and output the light refracted by said prism member in a predetermined range.

4. A device according to claim 3, wherein said condenser lens unit comprises a plurality of Fresnel lenses.

5. A device according to claim 3, wherein said condenser lens unit comprises a plurality of lenses arranged at a larger pitch than an array pitch of said prisms of said prism member.

6. A device according to claim 5, wherein each lens of said condenser lens unit is formed to oppose an odd number, not less than three prisms of said prism member.

7. A device according to claim 3, wherein said condenser lens unit comprises a lens array in which a plurality of fine lenses are arranged in each of longitudinal and lateral directions.

8. A device according to claim 7, wherein said fine lenses of said lens array are Fresnel lenses.

9. A device according to claim 2, wherein said light-condensing member comprises a plurality of columnar lenses with a substantially semicircular section arranged substantially parallel to one end face of said light guide plate, and each of said columnar lenses is arranged with a curved surface of said columnar lens opposing a corresponding one of the raised surfaces of the stepped surface of said light guide plate and with a flat surface of said columnar lens forming a predetermined angle with an envelope of the stepped surface.

10. A device according to claim 2, wherein said light-condensing member comprises a plurality of columnar lenses with a polygonal section arranged substantially parallel to one end face of said light guide plate, and each of said columnar lenses is arranged with one apex of the polygon of said columnar lens opposing a corresponding one of the raised surfaces forming the stepped surface of said light guide plate.

11. A device according to claim 1, wherein said light guide plate comprises a first partial light guide plate whose one end face is adjacent to said light source and another end face is distal to said light source, and a second partial light guide plate whose one end face is adjacent to said light source and another end face is distal to said light source, and the stepped surface comprises a first partial stepped surface formed on said first partial light guide plate and a second partial stepped surface formed on said second partial light guide plate, envelope planes of the first and second partial stepped surfaces being essentially equal to each other.

12. A device according to claim 1, wherein the stepped surface comprises a plurality of reflection regions for reflecting light incident from one end and a plurality of flat regions for outputting the light reflected by the reflection regions.

13. A device according to claim 1, wherein said light guide plate comprises optical interfaces which form a plurality of light guide regions in a one-to-one correspondence with steps on the stepped surface and guide light directed to the outside of said light guide regions in a direction of said light-condensing member.

14. A device according to claim 13, wherein the optical interfaces of said light guide plate are interfaces of low-refractive index layers formed in boundaries between the light guide regions and made from a substance having a refractive index smaller than a refractive index of said light guide plate.

15. A device according to claim 14, wherein said low-refractive index layers are air layers.

16. A surface light source device comprising:

a light source;

a light guide plate, formed from one block of an optically homogeneous transparent material, at one end of which said light source is arranged and which has an uneven surface having a plurality of projections for outputting light from said light source, which is incident from the one end, to a front surface;

a prism unit faced to the uneven surface of said light guide plate and including a plurality of prisms which refract exit light from said light guide plate in a direction in which an angle with respect to a normal to said light guide plate decreases; and

a light-condensing member arranged on an exit side of said prism unit and including a plurality of lenses which output exit light from said prism unit in a direction within a predetermined range.

17. A device according to claim 16, wherein the projections of said light guide plate are formed in a one-to-one correspondence with spaces between said prisms and have inclined surfaces for outputting light guided in said light guide plate.

18. A device according to claim 16, wherein the projections of said light guide plate form a plurality of prisms having light exit surfaces.

19. A liquid crystal display device including a surface light source, comprising:

a light source;

a light guide plate, formed from one block of an optically homogeneous transparent material, at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface;

a light-condensing member arranged to oppose the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range; and

a liquid crystal display element arranged on a light exit side of said light-condensing member and comprising a pair of substrates having electrodes opposing each other and a liquid crystal sealed between said substrates and oriented in a predetermined state.

20. A device according to claim 19, wherein

said light guide plate has a reflection surface for reflecting light incident from one end, and the stepped surface has a plurality of raised surfaces for outputting light guided by said light guide plate;

and

said light-condensing member comprises a prism member having a plurality of prisms so arranged as to refract exit light from the raised surfaces of the stepped surface in a direction in which an angle with respect to a normal to an envelope plane of the stepped surface decreases, and a condenser lens unit having a plurality of condenser lenses arranged in a light exit direction of said light-condensing member so as to condense and output the light refracted by said prism member in a predetermined range.

21. A device according to claim 19, wherein said light-condensing member comprises a plurality of Fresnel lenses.

22. A device according to claim 19, wherein said light-condensing member comprises a plurality of columnar lenses with a polygonal section arranged nearly parallel to one end face of said light guide plate, and each of said columnar lenses is arranged with one apex of the polygon of said columnar lens opposing a corresponding one of the raised surfaces forming the stepped surface of said light guide plate.

23. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range;

wherein said light-condensing member is a transparent plate formed from one block made of an optically homogeneous transparent material, said transparent plate integrally incorporating a prism unit on one side and a condenser lens unit on the other side, said other side having the prism unit arranged to face the stepped surface of said light guide plate.

24. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range;

wherein said light guide plate has a reflection surface for reflecting light incident from one end, and the stepped surface has raised surfaces for outputting light guided by said light guide plate;

wherein said light-condensing member comprises;

a prism member having an array of a plurality of prisms which refract exit light from the raised surfaces of the stepped surface in a direction in which an angle with respect to a normal to an envelope plane of the stepped surface decreases; and

a condenser lens unit arranged in a light exit direction of said light-condensing member and having an array of a plurality of condenser lenses which condense and output the light refracted by said prism member in a predetermined range; and

wherein said condenser lens unit comprises a plurality of lenses arranged at a larger pitch than an array pitch of said prisms of said prism member.

25. A device according to claim 24, wherein each lens of said condenser lens units is formed to oppose an odd number, not less than three prisms of said prism member.

26. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range;

wherein said light guide plate has a reflection surface for reflecting light incident from one end, and the stepped surface has raised surfaces for outputting light guided by said light guide plate; and

wherein said light-condensing member comprises a plurality of columnar lenses with a substantially semicircular section arranged substantially parallel to one end face of said light guide plate, and each of said columnar lenses is arranged with a curved surface of said columnar lens opposing a corresponding one of the raised surfaces of the stepped surface of said light guide plate and with a flat surface of said columnar lens forming a predetermined angle with an envelope of the stepped surface.

27. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range;

wherein said light guide plate has a reflection surface for reflecting light incident from one end, and the stepped surface has raised surfaces for outputting light guided by said light guide plate; and

wherein said light-condensing member comprises a plurality of columnar lenses with a polygonal section arranged substantially parallel to one end face of said light guide plate, and each of said columnar lenses being arranged with one apex of the polygon of said columnar lens opposing a corresponding one of the raised surfaces forming the stepped surface of said light guide plate.

28. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface; and

a light-condensing member faced to the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range;

wherein said light guide plate comprises optical interfaces which form a plurality of light guide regions in a one-to-one correspondence with steps on the stepped surface and guide light directed to the outside of said light guide regions in a direction of said light-condensing member.

29. A device according to claim 28, wherein the optical interfaces of said light guide plate are interfaces of low-refractive index layers formed in boundaries between the light guide regions and made from a substance having a refractive index smaller than a refractive index of said light guide plate.

30. A surface light source device comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a surface having a plurality of projections for outputting light from said light source, which is incident from the one end, to a front surface;

a prism unit faced to the surface of said light guide plate and including a plurality of prisms which refract exit light from said light guide plate in a direction in which an angle with respect to a normal to said light guide plate decreases; and

a light-condensing member arranged on an exit side of said prism unit and including a plurality of lenses which output exit light from said prism unit in a direction within a predetermined range;

wherein the projections of said light guide plate are formed in a one-to-one correspondence with spaces between said prisms and have inclined surfaces for outputting light guided in said light guide plate.

31. A liquid crystal display device including a surface light source, comprising:

a light source;

a light guide plate at one end of which said light source is arranged and which has a stepped surface whose thickness decreases step by step at a predetermined pitch from the one end to the other, and guides light from said light source to the stepped surface;

a light-condensing member arranged to oppose the stepped surface of said light guide plate to output exit light from the stepped surface of said light guide plate in a direction within a predetermined range; and

a liquid crystal display element arranged on a light exit side of said light-condensing member and comprising a pair of substrates having electrodes opposing each other and a liquid crystal sealed between said substrates and oriented in a predetermined state;

wherein said light-condensing member comprises a plurality of columnar lenses with a polygonal section arranged nearly parallel to one end face of said light guide plate; and

wherein each of said columnar lenses are arranged with one apex of the polygon of said columnar lens opposing a corresponding one of the raised surfaces forming the stepped surface of said light guide plate.

32. A device according to claim 31, wherein said low-refractive index layers are air layers.