| 摘要 |
PURPOSE:To provide a uniform wavelength region for transmission or reflection over the entire surface of a light interference film as well as the uniform reflectivity and transmittivity thereof and to eliminate color fringes and bright and dark fringes by locally changing the thicknesses of high refractive index layers and low refractive index layers in compliance with the incident angle distribution of light from a light source to the light interference film. CONSTITUTION:The thicknesses of the high refractive index layers 41 and low refractive index layers 42 constituting the light interference film 4 are made larger nearer the aperture edge of a substrate 3 in compliance with the distribution of the incident angles from the light source 1, by which dcostheta is made as uniform as possible. As a result, the reflection wavelength region of visible light and the transmission wavelength region of IR rays are made approximately uniform over the entire surface of the film 4 and the reflectivity and transmittivity thereof are made approximately the same in the reflectivity and transmittivity in the low incident angle position. The light radiation efficiency is improved and the IR rays in the radiation light are decreased.
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