• Triangular-sectioned glass cylinder which can be used to split light into its spectral components or to recombine it once divided, because of the differential rate at which glass refracts light of different wavelengths. diffraction gratings have largely replaced them in astronomical equipment.
  • A transparent optical material or lens, such as that made of glass, with no less than two polished plane surfaces which are at an angle relative to each other so as to reflect or refract light. A prism may be utilized, for instance, to disperse white light into its component colors, to produce plane-polarized light from unpolarized light, or to invert an image. Used, for instance, in cameras and binoculars. Also called optical prism.

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