| 摘要 |
PURPOSE:To prevent unevenness in luminance, etc., and enable the apparatus to be made thinner by forming a reflecting face on the bottom face of a housing which is parallel to a Fresnel cut to have its focus on the image of a light source which is projected on the reflecting face. CONSTITUTION:A Fresnel lens 4 is mounted on an open face opposite to the bottom face 2a of a housing 2 and a reflecting face 2b is formed on the whole or a part of the bottom face 2a. A Fresnel cut 4a has its focus on the image 3G of a light source 3 which is projected on the reflecting face 2b. The distance between the bottom face 2a and the Fresnel lens 4 is made 2D, at the center of which exists the light source. The focus of the Fresnel cut 4a is D in the absence of the reflecting face 2b, but because of the presence of the reflecting face 2b the focus is capable of being formed on the image 3G and the focal distance of the Fresnel cut 4a becomes 3D accordingly, ie. three times as long. The amount of fluctuations in the angle of incidence of light incident on the lens 4 from the light source 3 is thus reduced to decrease differences in luminance. |
