A number signifying how well a material can refract light. Usually specified as n by scientists, the index of refraction of a material depends on its composition and density. Water has an index of refraction of 1.333; n of air is nearly 1.0; and n of a vacuum is exactly 1.0.
The index of refraction is the ratio of the speed an electromagnetic wave in vacuum to the speed of the electromagnetic wave in a particular medium. typically denoted by the lowercase . n = c/v. The index of refraction is a property of the medium in question, and the incident electromagnetic wave. In general, they index of refraction may depend on on the frequency of the incident wave, and on its polarization. A media in which the index of refraction depends on the frequency of the electromagnetic wave is said to be dispersive. A media in which the index of refraction depends on the polarization of the incident wave is said to be birefringent
The ratio of the speed of light in air to its velocity in another medium; determines how much light bends as it passes through a lens, e.g., high-index flint glass bends light more than low-index crown glass does.