| 摘要 |
PURPOSE: To improve the reflection efficiency at a reflection surface and to brighten the ray arriving at an objective surface by forming an inclination on an incident surface in order to collimate the ray arriving at the reflection surface from the incident surface to approximately parallel rays. CONSTITUTION: This light guide 2 has the incident surface 21 which is formed of a transparent acrylic resin and receives the ray L1 from a light source 1, the reflection surface 22 which totally reflects the ray L2 from the incident surface 21 and the objective surface 23 which irradiates the ray L3 reflected by the reflection surface 22 to an illuminating object 3, such as switch or nameplate of instruments. The inclined part 21a is formed on the side further from the light source 1 of the incident surface 21. The angle d[ deg.] of the inclined part 21a is set at an angle at which the ray L2 arriving at the reflection surface 22 from the incident surface 21 can be collimated to the approximately parallel rays. As a result, the incident angleθ3 of the ray L2 with the reflection surface 22 attains the critical angleθ0 (about 42 [ deg.[) or above and the rate at which the ray L2 is totally reflected at the reflection surface 22 is increased. The ray L3 arriving at the objective surface 23 is thus brightened.
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