In optical devices, optical prism is a piece of glass or other transparent material cut at a precise angle and plane, which can be used to analyze and reflect light.
Ordinary glass triangular prisms can separate white light into its constituent colors, called frequency spectrum. Each color or wavelength that makes up white light is bent or refracted, but the amount is different. Shorter wavelengths (wavelengths toward the purple end of the spectrum) bend the most, while longer wavelengths (wavelengths toward the red end of the spectrum) bend the least. This type of prism is used in some spectroscopes, instruments that analyze light and determine the identity and structure of materials that emit or absorb light.
Optical prisms refract light to reflect (reflection prism), disperse (dispersion prism) or split (optical beam splitter) light. The prism is usually made of glass, but any material can be used as long as the material is transparent and suitable for the design wavelength. Common materials include glass, plastic and fluorite.
Optical prisms can reverse the direction of light through internal reflection, so they are useful in binoculars.
Depending on the application, optical prisms can be made in many different forms and shapes. For example, the Porro prism is composed of two prisms. The two prisms can invert the image as well as the image, and are used in many optical observation instruments, such as periscopes, binoculars and monoculars.