LIGHT DIFFUSION SHEET AND PROJECTION SCREEN

摘要

PROBLEM TO BE SOLVED: To provide a light diffusion sheet which does not deteriorate surface brightness or a contrast due to stray light, has few angle dependencies and little scatter reflection of external light, and to provide a projection screen using the light diffusion sheet. SOLUTION: In the light diffusion sheet in which a plurality of unit lenses are formed in one-dimensional or two-dimensional direction, the unit lens has an almost trapezoidal cross-sectional shape, and makes a trapezoidal lower bottom into a light beam receiving part and an upper base into a light emitting part, and is formed of a material having a predetermined refractive index N1. A transparent low refractive index layer having a refractive index N2 lower than N1 is formed at the portion of the trapezoidal oblique side of the unit lens. When the length of the trapezoidal upper base is set to be T, the height is set to be H and the angle formed by the trapezoidal oblique side and the normal of the light emitting part is set to beθ, the light diffusion sheet satisfies the relations of sin(90 degrees -θ)>N2/N1, N1<1/sin2θand 0