Prisms

Prisms are transparent optical elements with flat, polished surfaces arranged to refract light. The most common form is a triangular prism with two triangular faces and three rectangular faces, used to disperse light into its constituent colors.

Light entering a prism changes speed at each surface, bending according to Snell's law. Because the refractive index of most materials varies with wavelength, shorter wavelengths (blue) are bent more than longer wavelengths (red). As a result, a beam of white light emerges spread into a spectrum. The degree of deviation also depends on the prism's apex angle and the angle of incidence.

Prisms are made from glass types such as crown and flint glass, or from materials like fused silica and acrylic. They can be used singly or in combinations to minimize or maximize dispersion, and in some cases to reflect or redirect light (e.g., roof prisms and periscopes).

Common applications include spectroscopy, where prisms separate light for analysis; optical instruments for guiding or dispersing light; laser beam shaping and dispersion compensation; and decorative or educational uses such as rainbow prisms.

Historically, prisms played a key role in studying white light. Isaac Newton demonstrated that sunlight can be separated into a spectrum using a glass prism.

See also: Snell's law, dispersion, spectroscopy.