Spread illumination apparatus having trapezoidally-shaped grooves

Abstract

The present invention provides a spread illuminating apparatus for improving the machinability and durability of a molding die for a transparent substrate and obtaining an excellent light reflection. In a light reflection pattern comprising grooves and substantially flat portions adjacent to the grooves and formed on an upper surface of the transparent substrate in parallel to the optical axis of a bar-like light conductive member located close to an end surface of the transparent substrate, the grooves are each formed substantially trapezoidal in section with their bottom surface defining a shorter side of trapezoid. The inclination angle of an inclined surface positioned closer to a light source is set to range between 35° and 55°, the inclination angles of both the substantially flat portions and the bottom surfaces are set to range between −5° and +5°, the width of the substantially flat portions is set to be constant, and the width and depth of the grooves gradually increase in proportion to the increase in distance from the light source.

Dependencies are inferred from the claim text.