| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical sheet capable of reducing warping due to water absorption without using material having a low coefficient of water absorption, and to provide a surface light source device using the optical sheet. SOLUTION: The optical sheet comprises: a first layer 161 close to an emission surface 163 formed of prism shapes; and a second layer 162 close to an incident surface 164, wherein the coefficient of water absorption of the first layer 161 is less than the coefficient of water absorption of the second layer 162. Further, when the surface area of the incident surface and the surface area of the emission surface per unit sheet area of a light control sheet 16 are respectively denoted by X, Y, the coefficient of saturation water absorption of material forming the first layer 161 is denoted by A% and the coefficient of saturation water absorption of material forming the second layer 162 is denoted by B%, the optical sheet satisfies the relation: 0.8≤AX/BX≤1.25. COPYRIGHT: (C)2008,JPO&INPIT |
