| 摘要 |
A surface light source device improves the quality of illumination without producing dark lines between neighboring light guide plates even when a plurality of light guide plates are used in combination. This surface light source device is formed by combining a plurality of LED/light guide plate units, and light guide plate (4) has: light emitting area (8) of a square shape from a plan view; extended area (10) which is positioned extending outward from a pair of neighboring sides (8a) and (8b) in four sides (8a) to (8d) defining the outer rim of this light emitting area (8); and incidence surface area (11) on which light from LED (6) is incident. Each light guide plate (4) has a symmetrical shape with respect to one of the diagonal lines of light emitting area (8), and is combined by making its orientation uniform in the same direction. At this time, sides (8c) and (8d) in which the extended area of light emitting area (8) of one light guide plate (4) are aligned with sides (8a) and (8b) in which extended areas (10) of other neighboring light guide plates (4) are formed, and extended areas (10) of other light guide plates (4) are placed in the back surface side of light emitting area (8) of one light guide plate (4).
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