| 摘要 |
PROBLEM TO BE SOLVED: To provide a lighting device that can make the illuminance distribution in an effective lighting range more uniform by reducing the intensity of concentric circular interference fringes on a lit surface without influencing imaging performance even when a transmission type optical plane plate for illuminance distribution correction is introduced. SOLUTION: The lighting device which lights the lit surface by using coherent illumination light emitted by a light source has a transmission type optical plane plate such that the optical path length from an incidence surface to a projection surface is less than a half as long as the coherence distance of the illumination light and the product of the reflection factor (%) of the incidence surface and the reflection factor (%) of the projection surface when the illumination light is incident is≥0.01, and also satisfies 2nWtanθ≥λorθ≥3 seconds, whereθis the angle that the incidence surface and projection surface contains,λthe wavelength of the illumination light from the light source, W the minimum width of the illumination light, and (n) the refractive index of the material occupying the space from the incidence surface to the projection surface. COPYRIGHT: (C)2004,JPO
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