To provide a light guide plate having a high light utilization efficiency and can emit light having little luminous irregularities and can obtain a bright convex distribution in the vicinity of a central part of a screen as compared with a peripheral part, and provide a surface lighting device.
The light guide plate includes two layers comprising a first layer and a second layer which are superimposed in an almost vertical direction to a light emission surface and have different particle concentrations of diffusion particles. The second layer has a cross-sectional shape having at least a part in which the thickness in an almost vertical direction to the light emission surface is continuously increased up to the maximum in a direction as it goes apart from a light incident surface, and the diffusion particles are dispersed so that a synthetic scattering cross-sectional area S in a direction of the two layers in a position along a direction almost parallel with the light emission surface may be continuously and monotonously increased as it goes apart from the light incident surface, and the maximum value Smax and the minimum value Smin of the synthetic scattering cross-sectional area S shall satisfy 1.25≤Smax≤2.2, and moreover 0.90≤Smin≤1.6.
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IWASAKI OSAMU
Haruko Sanwa
Hideaki Ito
Fumio Mitsuhashi