For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. Refraction of a light ray. The refractive index determines how much light is bent, or refracted, when entering a material. read more
Refraction is therefore a result of the velocity of light changing as it passes from one medium (vacuum) to the other (eg. glass). If the refraction index of some medium is therefore [itex]1.0[/itex] no refraction will take place. read more