Patent ID: 7431480

Claim:
An optical element, which is positioned in relation to a light source device, to convert the diffuse illumination light radiated by the light source device into substantially parallel light, comprising: a primary surface- 1 whereon the diffuse illuminating light radiated by the light source device is incident; a primary surface- 2 formed in a concave cross-sectional shape when viewed from the primary surface- 1 , which reflects only illuminating light incident from the primary surface- 1 ; a primary surface- 3 formed in a convex cross-sectional shape when viewed from the primary surface- 2 , which reflects only diffuse illuminating light radiated by the light source device; and a primary surface- 4 which radiates illuminating light incident from the primary surface- 1 and illuminating light reflected by the primary surface- 2 , wherein the primary surfaces- 1 through - 4 are located at positions such that light beams reflected by the primary surface- 2 and light beams reflected by the primary surface- 3 are substantially parallel.