Surface light source device and a liquid crystal display device

PROBLEM TO BE SOLVED: To provide a prism sheet capable of widening an angle of field while maintaining high luminance in the direction of front. SOLUTION: A light incident surface has a prism line in which unit prisms of triangular prism shape are arranged in parallel. Each unit prism has a triangular prism shape formed from a first slant face and a plurality of flat faces of different inclination angles and defined by a second slant face opposite the first slant face. A first slant face, which is one of adjacent unit prisms, and a second slant face, which is the other, are arranged so as to face each other. The first slant face has an inclination angle at which a first directional light that has the maximum intensity in a predetermined direction can be made incident on it. Each of flat faces included in the second slant face provides second directional light that has the maximum intensity at an angle differing according to a component in which the first directional light has reached each flat face. Emission light composed of all the second directional light has the maximum intensity in the direction of normal. Each flat face of the prism sheet has an inclination angle at which internal reflection is caused so that the peak of the intensity distribution is gentler than that of the first directional light. COPYRIGHT: (C)2013,JPO&INPIT