Surface light source device, and liquid crystal display device, sign display apparatus and traffic sign display apparatus using the surface light source device

• US 20010030861A1
• Filed: 04/16/2001
• Published: 10/18/2001
• Est. Priority Date: 02/01/1996
• Status: Active Grant

• Current Assignee: Mitsubishi Rayon Company Limited (Mitsubishi Chemical Holdings Corporation)
• Original Assignee: Mitsubishi Rayon Company Limited (Mitsubishi Chemical Holdings Corporation)
• Inventors: Oda, Mosaharu, Hayashi, Yasuko, Chiba, Issei
• Granted Patent: US 6,332,691 B2
• Time in Patent Office: Days
• US Class Current: 362/31
• 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 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

A surface light source device, comprising a light source (2); a light conductor (1) which has a light incident face (11) on at least one side end surface thereof which confronts the light source (2), and a light emitting face (12) on one surface thereof which is substantially perpendicular to the light incident face (11); and a light angle varying sheet (3) which is disposed at a side of the light emitting face (12) of the light conductor (1). wherein at least one of the light emitting face (12) and a back surface (13) of the light conductor (1) comprises a minute structure having an average slant angle of 0.5 to 7.5 degrees. The light angle varying sheet (3) may comprise a prism sheet having a plurality of prisms (31) which are formed parallel to one another on at least one surface thereof. The minute structure may comprise a roughened surface which includes a plurality of fine convex members each having a substantially spherical surface or a plurality of prism arrays having slant surfaces which extend parallel to said light incident face (11) and which have an average slant angle of 0.5 to 7.5 degrees.

Claims

1. A surface light source device comprising:

a light source;

a light conductor which has a light incident face on at least one side end surface thereof which confronts said light source, and a light emitting face on one surface thereof which is substantially perpendicular to said light incident face; and

a light angle varying sheet which is disposed at a side of said light emitting face of said light conductor,

wherein at least one of said light emitting face and a back surface of said light conductor comprises a minute structure having an average slant angle of 0.5 to 7.5 degrees.

2. The surface light source device as claimed in

claim 1

, wherein said light angle varying sheet comprises a lens sheet having a plurality of lenses which are formed parallel to one another on at least one surface thereof.

3. The surface light source device as claimed in

claim 2

, wherein said lens sheet is a prism sheet having a plurality of prisms which are formed parallel to one another on at least one surface thereof.

4. The surface light source device as claimed in

claim 1

, wherein said minute structure comprises a roughened surface which includes a plurality of fine convex members each having a substantially spherical surface.

5. The surface light source device as claimed in

claim 4

, wherein a ratio of a minute average radius of curvature to an average period of said convex members is set to 3 to 10, and a ratio of an average deviation of a distribution of the minute average radius of curvature to the minute average radius of curvature is set to 0.85 or less.

6. The surface light source device as claimed in

claim 4

, wherein said roughened surface includes areas which have a minute average slant angle of 20 degrees or more at an occupation rate of 2% or less.

7. The surface light source device as claimed in

claim 1

, wherein said minute structure comprises a plurality of lens arrays having slant surfaces which extend parallel to said light incident face and which have an average slant angle of 0.5 to 7.5 degrees.

8. The surface light source device as claimed in

claim 7

, wherein said lens arrays comprise prism arrays.

9. The surface light source device as claimed in

claim 7

, wherein said lens arrays comprise lenticular lens arrays each having an arcuate shape in section.

10. The surface light source device as claimed in

claim 1

, wherein the light emission rate from said light emitting face of said light conductor is set to 1% to 4.5%.

11. The surface light source device as claimed in

claim 1

, wherein a peak light having a maximum light intensity which is emitted from said light emitting face of said light conductor is emitted at an angle of 65 degrees or more with respect to a normal to said light emitting face.

12. The surface light source device as claimed in

claim 1

, wherein an intersecting angle between a direction of a peak light having a maximum intensity emitted from said light emitting face of said light conductor and a direction of light having 50% of the maximum light intensity is equal to 20 degrees or less.

13. The surface light source device as claimed in

claim 1

, wherein said light conductor is designed so that a ratio (L/t) of a length (L) from the light incident face to an end face confronting said light incident face and a thickness (t) of said light conductor is set to 200 or less.

14. A liquid crystal display device, comprising the surface light source device as claimed in

claim 1

as a back light.

15. The liquid crystal display device as claimed in

claim 14

, wherein a dispersion rate (R%) of the brightness of light emitted from said light emitting face of said light conductor is set to 30% or less.

16. A sign display apparatus, comprising the surface light source device as claimed in

claim 1

as a back light.

17. The sign display apparatus as claimed in

claim 16

, wherein a dispersion rate (R%) of the brightness of light emitted from said light emitting face of said light conductor is set to 250% or less.

18. A traffic sign display apparatus, comprising the surface light source device as claimed in

claim 1

as a back light.

19. The traffic sign display apparatus as claimed in

claim 18

, wherein a dispersion rate (R%) of the brightness of light emitted from said light emitting face of said light conductor is set to 450% or less.