PRISM SHEET AND BACK LIGHT

摘要

PROBLEM TO BE SOLVED: To provide a prism sheet with which higher luminance may be attained by effectively directing the light from a plane illuminant to a front surface direction and a back light using the same. SOLUTION: A prism array 12 is formed on one surface of the sheet and the other surface is formed on a smooth surface 14. The sections of the respective prisms of the prism array I 2 are formed to a trapezoidal shape and the angleθ1 of the one slope thereof is 50 to 60 deg.. The angleθ2 of the other slope is 80 to 90 deg. and the pitch (a) of the prism array is 30 to 120μm. The angleθ2 of the slope of the trapezoidal shape exists on the light source side not shown in Fig., with respect to the angleθ1 . This prism sheet is so arranged that the smooth surface 14 side faces the plane illuminant. The prism sheet is preferably thermosetting polyurethane and a transparent resin material into which transparent dispersion materials are dispersed is adequately used for the plane illuminant.