| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-size optical sheet, an optical unit and a back light unit in which light beams can be introduced nearer to the direction to the front face of the screen of a liquid crystal display device without decreasing the efficiency for the light source. SOLUTION: The optical sheet 1 is composed of a lower base part 2 and an upper fitting part 4 which are engaged in the vertical direction with almost no gap between them. The base part 2 and the fitting part 4 are formed from materials of different refractive indices. The base part 2 has a plurality of triangular portions 3 arranged parallel to one another and each having a triangular cross section, and each triangular portion 3 has a first side face on the left and a second side face on the right. The triangular portion is formed in such a manner that the angle formed between the first side face and the lateral direction of the triangle is made equal to or larger than the angle between the direction of the peak of the beams entering the base part 2 from a light guide plate 7 by refraction and the lateral direction, and that the direction of the peak of the beams entering the fitting part 4 from the second side face of the base part 2 by refraction is nearer to the upward direction than the direction of the peak of the beams propagating in the base part 2 to the second side face. |
