What is unit of refractive index?

The unit of refractive index is dimensionless. It is defined as the ratio of the speed of light in a vacuum to the speed of light in a medium. Refractive index is used to describe how much a ray of light is bent when it passes from one medium to another, such as from air to glass. The higher the refractive index, the more the light is bent. Materials with a higher refractive index are commonly used in lenses for cameras, telescopes, and eyeglasses. The refractive index of a material can be measured using a refractometer.