FRESNEL LENS WITH CAVITIES

摘要

An exemplary Fresnel lens includes a flat emitting surface and a plurality of annular Fresnel lens elements at an opposite side thereof to the emitting surface. Each of the Fresnel lens elements has a non-lens surface perpendicular to the emitting surface and a Fresnel lens surface adjoining the non-lens surface with an acute angle. Each of the Fresnel lens elements has a plurality of spaced cavities defined in the non-lens surface.