| 摘要 |
PURPOSE:To reduce the loss of a quantity of incident light and to obtain uniform brightness by forming some of prisms constituting a lens so that a part of light beam incident to a lens surface is reflected totally by a non-lens surface and then projected to a projection surface. CONSTITUTION:A part 1 uses conventional prisms and a part 2 are prisms employed to this invention. Namely, a conventional prism group 1 is used up to specific distance from the center and the circumferential part consists of the new prisms 2. The transmission characteristics of the prisms 2 are as shown in a diagram and each prism 2 consists of a lens surface 21 and a non-lens surface 22; and part of light incident of the lens surface 21 is reflected totally by the non-lens surface 22 and projected. When incident light L1' travels straight without reaching the non-lens surface 22 and reaches the lens surface 21, its loss part L' is small, so the quantity of effective light is large. |
