Prisms

An optical prism is a transparent optical element with a flat polished surface designed to refract light. At least one face must be angled. An element with two parallel faces is not a prism. The traditional geometric shape of an optical prism is a triangular prism with a triangular base and rectangular sides, and in colloquial usage, "prism" usually refers to this type. In fact, some types of optical prisms do not take the form of geometric prisms. Prisms can be made from materials that are transparent to the designed wavelength. Typical materials are glass, acrylic, and fluorite.