What is the bending of light called?

The bending of light is called refraction. It happens when light passes from one transparent medium into another—such as from air into water or glass—and changes speed, causing its path to change direction.

Refraction is easiest to notice when light crosses a boundary at an angle. Entering a denser optical medium, such as glass, generally bends light toward the normal line; entering a less dense medium bends it away. The amount of bending depends on the refractive indices of the two materials and the angle of incidence, as described by Snell’s law.

Refraction explains why a pencil partly submerged in water can look bent and why swimming pools appear shallower than they really are. Camera lenses, eyeglasses, microscopes and telescopes all use carefully shaped pieces of glass or plastic to redirect light and form images.

A closely related phenomenon is dispersion. Because different colors travel at slightly different speeds in a material, a prism or raindrop can refract them by different amounts, separating white light into a spectrum and helping create rainbows.