Refraction of light
From The Glossary of Digital Photography
The bending of light rays when the light changes speed, usually as it passes through one medium into another. An example would be when a light ray enters a lens. Refraction of light is part of the concept that led to the development of lenses, which are designed to bend light rays and focus them at a point behind the lens. Snell's Law is used to calculate refraction that occurs. See also angle of refraction; Snell's Law
