| 摘要 |
PURPOSE:To give a uniform light quantity distribution to light which has passed through a lens by providing an adjusting means for the light quantity distribution which gives the light a light quantity distribution based upon a function of the angle of a light beam passed through the lens to the optical axis of the lens. CONSTITUTION:An aspherical mirror 11 as the light quantity distribution adjusting means is provided concentrically with an annular light source 10, the lens L is provided coaxially over the light source 10, and a Fresnel reflecting plate 12 is arranged under the light source 10 and mirror 11. The light from the light source 10 is directed to the Fresnel reflecting plate 12 through the mirror 11, the reflected light from the mirror 11 is directed to the opposite side across the optical axis, and the mirror 11 is so designed as to have illuminance on the surface of the Fresnel reflecting plate 12 as shown by a curve 13. The light reflected by the Fresnel reflecting plate 12 travels upward and passes through the lens L to reach a projection surface 20 through a plane mirror 14. The curve 13 is so determined that the illuminance on the surface of the Fresnel reflecting plate 12 is a reciprocal of cos<4>theta, where theta is the angle of the light incident to the lens L to the optical axis.
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