| 摘要 |
PURPOSE: To ensure luminance sufficient for practicable use, to widen a light emission range and to obtain brightness, easy visibility and good image quality feeling without fatigue by successively arranging first and second light controllable sheets which are respectively specific on a light transmission plate. CONSTITUTION: The rear surface of the light transmission plate 14 is arranged with a reflection plate 16 and its front surface is provided with the first and second light controllable sheets 21, 22. The sheet 21 has a rugged shape and the sectional shape crossing the rugged lines thereof is formed to an isosceles triangle shape of a vertex of 70 deg. to 120 deg.. The sheet 22 has a rugged shape and the sectional shape crossing the rugged lines thereof is formed to a corrugated shape by continuous curves. Such sheets 21, 22 are successively arranged on the light transmission plate 14, by which the abrupt degradation in the luminance admitted when only the sheet imparted with a prism shape is used is prevented without degrading the luminance in a normal direction by successively arranging such sheets 21, 22 on the light transmission plate 14. Consequently, a drastic contrast change does not appear any more and, therefore, bright areas and dark are no longer visually recognized even if the observation direction is successively inclined from the front. |
