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PROBLEM TO BE SOLVED: To provide a light guide plate which has a large and thin shape and is high light use efficiency and can emit light with low luminance unevenness, can obtain a convex or bell-shaped light distribution and can be easily produced.
SOLUTION: The light guide plate has two layers which are piled up in a direction approximately perpendicular to a light-emitting surface and are different in particle concentration of scattered particles. A combined particle concentration of the light guide plate changes in the direction perpendicular to a light-incident surface by respective changes of the thicknesses of the two layers in the direction approximately perpendicular to the light-emitting surface, and 0.3 mm≤Tlg≤4 mm and 0.3≤tcen/Tlg≤1 are satisfied where Tlg is a thickness in the direction perpendicular to the light-emitting surface and Tcen is the maximum thickness of the second layer.
COPYRIGHT: (C)2013,JPO&INPIT
【課題】大型かつ薄型な形状であり、光の利用効率が高く、輝度むらが少ない光を出射することができ、中高なあるいは釣鐘状の明るさの分布を得ることができ、かつ、製造が容易な導光板を提供する。【解決手段】光出射面に略垂直な方向に重なった、散乱粒子の粒子濃度が異なる2つの層を有し、光入射面に垂直な方向において、2つの層の、光出射面に略垂直な方向の厚さがそれぞれ変化して、導光板の合成粒子濃度が変化し、かつ、光出射面に垂直な方向の厚さをTlgとし、第2層の最大厚さをtcenとすると、0.3mm≦Tlg≦4mm、0.3≦tcen/Tlg≦1を満たす、ことにより上記課題を解決する。【選択図】図2