| 摘要 |
PROBLEM TO BE SOLVED: To simplify a back light unit as a whole and reduce a cost by applying a diffusion treatment to a prism sheet constituting the back light unit for a liquid display. SOLUTION: A back light unit 1 is arranged such that a light guide plate 3 is provided at the back face thereof with a reflection sheet 2, at the upper face thereof with a diffusion prism sheet 4, and at the side face thereof with a light source. A plurality of reflection grooves 3a are formed at the upper face of the light guide plate 3 on a side opposite to the reflection sheet 2. The diffusion prism sheet 4 is made of a plate material having light transmission property such as plastic. Reflection grooves 6 are formed on the diffusion prism sheet 4, and further, diffusion grooves each having a V-shaped cross section are injection-molded on a side opposite to the reflection grooves 6. The cross-sectional shape of the diffusion groove is not limited to a V shape, and arcuate, trapezoidal and other shapes may be allowed. |
