FRESNEL LENS SHEET, TRANSMISSION SCREEN USING THIS, AND REAR TRANSMISSION DISPLAY UNIT

摘要

A Fresnel lens sheet has an entrance surface ( 1 a) and an exit surface ( 1 b). A plurality of prisms ( 2 ) each having a refraction surface ( 3 ) and a total-reflection surface ( 4 ) are formed on the entrance surface ( 1 a). Light rays projected by a light source (M) disposed on the side of the sloping refraction surfaces ( 3 ) onto the entrance surface ( 1 a) are refracted at the refraction surfaces ( 3 ), and the refracted light rays are totally reflected by a total-reflection surfaces ( 4 ) in a direction substantially perpendicular to a sheet surface ( 1 c). Angles (alpha) between the refraction surfaces ( 3 ) and the total-reflection surfaces ( 4 ) corresponding to the refraction surfaces ( 3 ) of all the prisms ( 2 ) are substantially equal to each other. The angle delta between the refraction surface ( 3 ) of the prism (P 2 ) farthest from the light source (M) and the sheet surface ( 1 c) is approximately equal to a right angle.