Diffraction type light-condensing film and planar light source device using the same

Abstract

Provided are an easy-to-handle thin diffraction type light-condensing film exhibiting high light transmissivity and condensation ability, and a planar light source device using the film. A hologram optical element using diffraction/interference phenomena based on wave properties of light is used instead of a conventional prism sheet using refraction. As a result, the diffraction type light-condensing film and the planar light source device have high light transmissivity and are thin. In the diffraction type light-condensing film, dependence of bending angle on wave length is low and light entering from an oblique direction is bent in the vertical direction and emitted with spectral separation of white light suppressed. High light-condensation impossible in a conventional optical element is realized by suppressing angular variation in emission light for angular variation in incident light.