Illumination optical system and an illumination lens element

摘要

An illumination optical system includes a luminous body, and an illumination lens element through which light rays from said luminous body is diffused and emitted. The illumination lens element has peaks and troughs alternately provided on an incident surface or an exit surface thereof. A cross-sectional shape of the peaks and troughs is a curved surface defined by a periodic function which can be differentiated, or the peaks and troughs are formed by a plurality of straight lines approximating the curved surface.