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As light moves from one medium (e.g. air) to another denser medium (the glass of the prism), it is slowed down and as a result either bent (refracted) or reflected. The angle that the beam of light makes with the interface as well as the refractive indices of the two media determine whether it is reflected or refracted, and by how much (see refraction, total internal reflection).

Reflective prisms are used to reflect light, for instance in binoculars, since they are easier to manufacture than mirrors. Dispersive prisms are used to break up light into its constituent spectral colors because the refractive index depends on frequency (see dispersion); the white light entering the prism is a mixture of different frequencies, each of which gets bent slightly differently. Blue light is slowed down more than red light and will therefore be bent more than red light. There are also polarizing prisms which can split a beam of light into components of varying polarization.

Until Isaac Newton, it was thought that prisms added colors to white light. Newton placed a second prism such that a separated color would pass through it and found the color unchanged. He concluded that prisms separate colors. He also used a lens and a second prism to recompose the rainbow into white light.

1 Types of prisms

Reflective prisms:

• PentaprismA pentaprism is a five-sided reflecting prism used to deviate a beam of light by 90°. The beam reflects inside the prism twice, allowing the transmission of an image through a right angle without inverting it (i. without changing the image's handedness) a
• Porro prismIn optics, a Porro prism named for its inventor Ignazio Porro, is a type of reflection prism used in optical instruments to alter the orientation of an image. It consists of a block of glass shaped as a right geometric prism with right-angled triangular e
• Porro-Abbe prism
• dove prismA dove prism is a type of reflective prism which is used to invert an image. Dove prisms are shaped from a truncated right-angle prism. A beam of light entering one of the sloped faces of the prism undergoes total internal reflection from the inside of th
• dichroic prismA dichroic prism is a prism that splits light into two beams of differing wavelength ( colour). They are usually constructed of one or more glass prisms with dichroic optical coatings that selectively reflect or transmit light depending on the light's wav
• Amici prism

Dispersive prisms:

• Abbe prismOptics In optics, an Abbe prism named for its inventor, the German physicist Ernst Abbe, is a type of constant deviation dispersive prism similar to a Pellin-Broca prism. The prism consist of a block of glass forming a right prism with 30°-60°-90° triangu
• Pellin-Broca prism
• triangular prism

Polarizing prisms:

• Wollaston prism