| 摘要 |
A surface illuminant device for illuminating a short-distance observation picture plane, capable of easily being enlarged in area without inviting a non-uniformity in visibility, the device comprising a light guide (12), a light reflection member (18), a linear light source disposed to extend in a Y-direction along a light incident end face in a Y-Z plane of the light guide (12), and a prism sheet (20) for converting a light advancing direction. The light guide (12) has a light outgoing mechanism of a fine unevenness structure for emitting from a light outgoing surface (12-3) an incident light from the linear source, and a light focusing means for acting on the light passed through the light guide (12) and the prism sheet (20) to allow it to leave in a focused status. The light focusing means is formed so that a prism apex angle alpha, an inclination beta with respect to a normal to the prism sheet, a change rate gamma of beta with respect to a prism arraying direction, and a prism arraying pitch P satisfy 55 deg.<=alpha<=75 deg., -20 deg.<=beta<=+20 deg., 0.2 deg./cm<=gamma<=1.5 deg./cm, 10 mum <=P<=1000 MUM.
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