Optimum riser angle for fresnel lenses in projection screens

摘要

a Fresnel lens for use in rear projection screens wherein said lens has a plurality of facets facing away from the light source and each of said facets has an optimal riser angle, said riser angle varying from the center to the outer edge of said lens as a function of the focal length the refractive index, the angular subtense of the exit pupil and the radial distance from the center of the lens, thereby improving the efficiency of the Fresnel lens.