Surface light source device, display device and optical sheet manufacturing method

1. A surface light source device comprising:

a plurality of light sources;

an optical sheet arranged to face the light sources, the optical sheet including a plurality of sections, each section centered on one of the light sources, wherein each section includes a transmission part having a plurality of through holes that are configured to transmit light emitted from the light sources, and a reflection part configured to reflect the light emitted from the light sources; and

a diffusion plate configured to diffuse the light transmitted through the transmission part, the diffusion plate being arranged to face the optical sheet and disposed on an opposite side relative to the light sources, wherein

each section of the optical sheet comprises a plurality of regions formed between concentric rectangles centered on its respective light source, the plurality of regions each comprising

a plurality of first through holes in each one of the regions, each first through hole having a hole diameter set according to a distance it is from the respective light source, and

at least one second through hole each having a hole diameter set to a different size from the hole diameter of the first through holes.

2. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that, in each section of the optical sheet, the hole diameter of the first through holes increases as moving away from the respective light source, and the hole diameter of the at least one second through hole is smaller than that of an adjacent through hole on a light source side or is larger than that of an adjacent through hole on an outer edge side.

3. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that the hole diameter of the at least one second through hole is set to a different size from the hole diameter of the first through holes so as to partially change luminance to suppress luminance unevenness.

4. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that outer ones of the through holes are arranged along an outer edge of the optical sheet and have the largest hole diameter among the through holes of the optical sheet.

5. The surface light source device according to claim 1 , wherein

the light sources are arranged relative to each other in a matrix, and

the optical sheet is configured such that the first through holes are arranged along a straight line in a direction parallel or perpendicular to a direction in which the light sources are arranged, and such that the at least one second through hole includes a plurality of second through holes that are arranged in a curved shape or a V-shape and are offset with respect to the straight line along which the first through holes are arranged.

6. The surface light source deice according to claim 5 , wherein

the first through holes are arranged along the straight line such that centers of the first through holes are aligned along the straight line, and

the second through holes are offset with respect to the straight line such that centers of the second through holes are offset with respect to the straight line.

7. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that a ratio of the through holes per unit area in a region directly above the respective light source is smaller than a ratio of the through holes per unit area in a region other than the region directly above the respective light source.

8. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that the hole diameter of the at least one second through hole has a size that differs from the hole diameter of the first through holes by one or several levels.

9. The surface light source device according to claim 8 , wherein

the at least one second through hole includes a pair of second through holes that are formed by mutually interchanging a pair of through holes with hole diameters that are different from each other by one or several levels.

10. The surface light source device according to claim 1 , wherein

the optical sheet have a through hole having the smallest hole diameter among the through holes of the optical sheet or have no through hole in a region directly above the respective light source.

11. The surface light source device according to claim 1 , wherein

the first through holes have same first hole diameter in each one of the regions of the optical sheet, and

the at least one second through hole has a second hole diameter that is different from the first hole diameter.

12. The surface light source device according to claim 11 , wherein

the second hole diameter of the at least one second through hole is larger than the first hole diameter of the first through holes.

13. The surface light source device according to claim 11 , wherein

the second hole diameter of the at least one second through hole is smaller than the first hole diameter of the first through holes.

14. A display device comprising:

the surface light source device according to claim 1 ; and

a display arranged to face the diffusion plate and disposed on an opposite side relative to the optical sheet.

15. An optical sheet manufacturing method for manufacturing an optical sheet configured to be arranged to face a plurality of light sources, the optical sheet including a plurality of sections, each section centered on one of the light sources, wherein each section includes a transmission part having a plurality of through holes that are configured to transmit light emitted from a light source, and a reflection part configured to reflect the light emitted from the light source, and comprises a plurality of regions formed between concentric rectangles centered on its respective light source, the optical sheet manufacturing method comprising:

providing, using a first tool, a plurality of first through holes in each one of the regions, each first through hole having a hole diameter set according to a distance it is from the respective light source; and

providing, using a second tool, at least one second through hole each having a hole diameter set to a different size from the hole diameter of the first through hole.

16. The surface light source device according to claim 1 , wherein

the optical sheet is configured such that, in each section of the optical sheet, the through holes are arranged relative to each other in a matrix.

17. The surface light source device according to claim 16 , wherein

the optical sheet is configured such that, in each section of the optical sheet, the through holes are arranged in a plurality of rows each having the same number of through holes and in a plurality of columns each having the same number of through holes.

18. The surface light source device according to claim 8 , wherein

the at least one second through hole includes a pair of second through holes that are formed by mutually interchanging a pair of through holes with hole diameters set according to distances they are from the respective light source.

19. The display device according to claim 14 , wherein

the optical sheet is configured such that, in each section of the optical sheet, the hole diameter of the first through holes increases as moving away from the respective light source, and the hole diameter of the at least one second through hole is smaller than that of an adjacent through hole on a light source side or is larger than that of an adjacent through hole on an outer edge side.

20. The display device according to claim 14 , wherein

the optical sheet is configured such that the hole diameter of the at least one second through hole is set to a different size from the hole diameter set of the first through holes so as to partially change luminance to suppress luminance unevenness.

21. The surface light source device according to claim 1 , wherein

at least one second through hole includes a plurality of second through holes each having a hole diameter set to a different size from the hole diameter of the first through holes, the position of each second through hole being determined as a function of its distance from the respective light source and the positions of the first through holes.