PRISM SHEET FOR PROJECTION IMAGE DISPLAY DEVICE, SHEET TYPE OPTICAL ELEMENT, METHOD FOR MANUFACTURING SHEET TYPE OPTICAL ELEMENT AND PROJECTION IMAGE DISPLAY DEVICE

摘要

PROBLEM TO BE SOLVED: To reduce the length from front to rear in a projection image display device and to increase the projection magnification while increasing uniformity of the luminance and sharpness of the screen. SOLUTION: The prism sheet is formed by densely arranging many thin prisms 3 each composed of a first inclined face 1 and a second inclined face 2. The angle 2 of the second inclined face is controlled to totally reflect the light transmitting through the first inclined face 1 and to allow the light to emit. The angleθ1 between the first inclined face 1 and the second inclined face 2 is <=45 deg.. A flat top face 5 is formed to connect the top edge of the first inclined face 1 and the top edge of the second inclined face 2. The angle of the top face 5 is controlled not to inhibit the light entering the first face 1 of the adjacent prism 3 and totally reflected by the second inclined face 2, and the angle is gradually varied over the prism parts 3 according to the incident angle of light. The prisms 3 have a function of a light diffusing layer or a tint layer, or a light diffusing layer or a tint layer is unitedly laminated in the exit side of the prisms 3. In the prisms 3 in the region near the optical axis A, the angles formed by the first and second inclined faces 1, 2 to the plane perpendicular to the optical axis A decrease to almost 0 in the prisms nearer to the optical axis A.