Refraction of light is the phenomenon of bending of a light wave when it enters into a medium from another where the speed of light is different. If the light wave passes from a  medium where speed is fast to a medium where the speed is slow the light wave bends towards the normal between the two medium and vice-verse. The extent to which bending takes place when the light enters from one medium to another medium depends on the speed of light in two medium. This is also calculate in terms of refractive index for media and is described quantitatively by Snell’s law