OPTICAL ELEMENT AND ILLUMINATION DEVICE INCLUDING OPTICAL ELEMENT

摘要

Provided is an optical element which optimizes the illuminance distribution in a surface to be illuminated. The optical element includes an incidence surface and an emission surface covering the incidence surface. The central axis of the optical element is set to be the Z-axis. The point of intersection between the Z-axis and a surface parallel to the flat surface on which a virtual light source is placed is set to be the origin which includes the emission point of the virtual light source. The X-axis and the Y-axis are set to pass through the origin vertically with reference to the Z-axis. The incidence surface is formed into a cap shape with a point intersecting with the Z-axis as the apex. The emission surface is recessed toward the incidence surface near the Z-axis, including an outwardly protruding portion around the recess. A virtual beam, travelling from the origin at an angle of &thetas;r with reference to the Z-axis, makes an angle of &thetas;i with the Z-axis right after passing through the incidence surface in the cross-sectional surface including the z-axis. The beam further makes an angle of &thetas;e with the Z-axis right after passing through the emission surface. The optical element is configured such that &thetas;e / &thetas;r ≥ 3 is always satisfied under the condition of &thetas;r ≤ 10°, and the maximum value of &thetas;e / &thetas;r is four or more; &thetas;e / &thetas;r < 3 is always satisfied under the condition of 20° ≤&thetas;r.