Britannica Sources used in this answer

How do prisms change the direction of a beam of light?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Are invisibility cloaks possible in reality? — optics Learn about researchers' attempts to create invisibility.

Prisms change the direction of a beam of light primarily through two optical phenomena: refraction and total internal reflection.12

Refraction

When light enters a prism from the air, it slows down because it is moving into a denser medium. This change in speed causes the light to bend, or refract, at the interface between the two materials. Because the refractive index of glass varies with wavelength, different colors of light bend by different amounts—a process known as dispersion. This allows prisms to separate white light into its constituent colors, or spectrum. The degree of bending at each interface is governed by Snell’s law.34562

Total Internal Reflection

Prisms can also change the direction of light through total internal reflection. When light traveling inside the prism strikes an internal surface at an angle greater than the critical angle, it is completely reflected back into the medium rather than passing through. This capability is used in instruments like binoculars and periscopes to redirect or reverse the path of light.12