| 摘要 |
PURPOSE:To adjust the quantity of illuminating light without changing the luminous intensity characteristic and the spectral characteristic by moving a zoom optical system, which is arranged between the incidence end of a light guide and a light source, along the optical axis. CONSTITUTION:In the stop state with a large aperture 9, a luminous flux passes a zoom optical system 6 and is set to a prescribed light distribution angle theta; and if a ring 8 is rotated in this state to narrow the aperture 9, a front lens 6A of the optical system 6 and the whole of the optical system 6 are moved to the light guide side, and a maximum incidence angle of the luminous flux incident on an incidence end surface 7A of a light guide 7 is kept at a certain light distribution angle by the optical system 6. Thus, the quantity of irradiated light which is discharged from the exit end of the light guide 7 is controlled variably while keeping the light distribution angle constant. Further, the spectral distribution shape to the incidence angle of the luminous flux incident on the incidence end surface 7A is kept.
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