Diffusely reflecting projection screen - has series of parallel triangular section grooves to reflect light rays twice

摘要

The projection screen has, on one part of the surface, identical parallel grooves. These are shaped to form a dihedral so that at least part of the light undergoes two successive diffusing reflections. The grooves are of triangular section, the dihedral angle being over 90 deg. and, between 90 and 100 deg. There are two groups of grooves which are symmetrical relative to the centre of the screen. The angle of the groove face furtherest from the screen centre is below 45 deg., preferably 35 to 45 deg.