PURPOSE: To obtain a clear image under powerful sunlight with simple constitution by forming a light guide optical block in such shape that fine prisms are continuously disposed at the light incident surface and that the face reflecting light in a specific direction after the light being guided is formed into the concave face having a reflecting layer.
CONSTITUTION: A light guide optical block 11 is formed into such shape that fine prisms are continuously arranged at a part of the surface, that a part of the remaining surface is formed into the concave face curved with specified curvature and that the surface of this concave face is provided with a reflecting layer 13. In order that the light emitted from a bulb 3 is efficiently led into the light guide optical block 11 through the prisms, it is necessary to make reflection at the prisms infinitely zero, so that the specific faces of the prisms are disposed vertically to the bulb. In order not to intercept light to the adjacent prism, it is so requested that the cross-sectional shape to the prism is a right- angled triangle with the apex angle being 90°.
KAI YASUAKI
IKUI SHUICHI
