| 摘要 |
PROBLEM TO BE SOLVED: To obtain a hollow system back light which enables light emitted from a light source to be irradiated efficiently in the direction of illumination. SOLUTION: A first prism sheet 7 and a second prism sheet 8 are arranged at a position opposite to a reflecting means with an interposed space part. A large number of prism columns 7a, which have a ridgeline 7b extending in parallel with the direction perpendicular to a center line of the light source, are formed in the first prism sheet 7. A large number of prism columns 8a of an isosceles triangle shape, in which an apex angle α and θ becomes approximately equal, if the peak angle of light distribution from the first prism sheet 7 is expressed by θ, are formed in the second prism sheet 8. These prism columns 8a, which have a ridgeline 8b extending in parallel with respect the center line of the light source, are formed on a plane which face opposite to the first prism sheet 7. Light transmitted through the first prism sheet 7 and the second prism sheet 8 becomes high in directivity and is irradiated efficiently in the direction of illumination, thus the brightness in the direction of the illumination is increased. |
