Prism plate for efficiently emitting light flux within a predetermined range, and liquid crystal indicator and indicator illumination method using the same

摘要

An information indicator suitable for information processors such as personal computers, word processors and the like includes a light source, a scattering plate which scatters light from the light source, an indicator plate irradiated with scattered light from the scattering plate, and a prism plate operatively arranged with respect to the scattering plate and the indicator plate and having a prism-like protuberance structure formed at a side thereof. The prism plate is so disposed that the prism-like protuberance structure faces the scattering plate, and the angle 2 theta constituting the prism-like protuberance structure is defined by the formula, 2 theta >2/3x( pi /2+2xarcsin (n'/n)), in this inequality, n is the refractive index of said prism plate medium, and n' is the refractive index of a material in which the prism plate is arranged.