| 摘要 |
A surface light source device of side light type is provided to achieve achieves both avoidance of pattern see-through and retainment of brightness around the front direction. Light of a lamp 1 surrounded by a reflector 6 is introduced into a wedge-shaped light guide plate 2 via an incidence surface 21. In the process that the light is guided toward a terminal surface 24 while being repeatedly reflected at an emission surface 22, back surface 23 or reflector 4 of the light guide plate 2, illumination light is gradually taken out of the emission surface 22. A light diffusion sheet 35 having weak light diffuseability and a prism sheet 30 are disposed outside emission surface 22. The light subject to weak light diffusion action through the weak light diffusion sheet 35 is incident from an incident surface 301 to the prism sheet 30 without loosing directivity, exiting from a bright surface 302 consisting of a number of prism arrays. This illumination light is mainly output toward around the front-directional at high brightness while having suitable expanse in direction of propagation. Simultaneously, pattern see-through phenomenon is suppressed to the extent so that it will no longer take place even when directly looking at bright surface 302.
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