Patent ID: 8690394

Claim:
An illuminating device having a light source for illuminating an irradiation target face with light, the illuminating device comprising: a transmission light amount adjusting unit arranged between the light source and the irradiation target face, the transmission light amount adjusting unit configured to adjust a transmission light amount so as to make a uniform illuminance distribution on the irradiation target face, wherein the transmission light amount adjusting unit comprises a light transmission plate laminate member having a plurality of light transmission plates that are constant in transmittance in a wavelength range of light to be transmitted therethrough, the plurality of light transmission plates are stacked by a stack number of the light transmission plates corresponding to an adjustment amount of the transmission light amount so as to reflect incident light at each boundary of front and back surfaces of each of the plurality of light transmission plates of the transmission light amount adjusting unit, and each of the plurality of light transmission plates is configured to be thinner in accordance with the stack number so that the whole thickness of the light transmission plate laminate member is constant.