| 摘要 |
PROBLEM TO BE SOLVED: To increase efficiencies of incidence and light guide, and reduce the diameter of the light guide duct, at the same time. SOLUTION: This consists of a light inlet 2 that opens at a side of an end of light guide duct 1, and a reflecting mirror 3, that is disposed at the end face of the guide duct 1 and lets the light introduced into the guide duct 1 from the light inlet 2 advance to the other end of guide duct 1. If denoting a for an end of the light inlet, c for its other end, d for the intersecting point of cross section normal to the light guide duct passing the above c and the other side face of the light duct,θfor light incidence angle made with the optical axis of the light incident inlet, andθmax for the largest incident angle required, the reflecting mirror that connects the a and d is made into a unit equipped with the first reflecting portion with a at an end and the second reflecting portion, that connects the other end b of the first reflecting portion with the d, and together, the first and second reflecting portions are set under the condition which agrees with the largest incident angle ofθmax.
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