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Abstract

There is provided a surface light source device which is excellent in whiteness and softness of a luminant surface and able to retain reflective appearance from occurring. The surface light source device is effectively applied to back lighting in a liquid crystal display. A fluorescent lamp (L) is disposed in the vicinity of an incidence surface (2) of a light guide plate (1). A prism sheet (4') having prism surfaces formed on both surfaces is disposed along an exiting surface (5). The prism sheet (4') is oriented such that prism rows (4a, 4b) on the inside surface run in the transverse direction of the light guide plate (1) while prism rows (4c, 4d) on the outside surface run in the longitudinal direction of the light guide plate (1). A reflector (3) is disposed along a back surface (6) of the light guide plate (1). Light emitted from the exiting surface (5) is led to the frontal direction by the action of the prism rows (4a, 4b) and then returned toward the light guide plate (1) after having been shifted in the transverse direction by the prism rows (4c, 4d). The history of a path of light emitted from the prism sheet (4') is diversified through this process, thereby improving visual characteristics.

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First Claim