The refractive index of glass is a measure of its ability to bend light. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the glass. The higher the refractive index, the more the light is bent. Glass has a refractive index of around 1.5, which means that light is bent by about 50% when it enters glass from air. This bending of light is what makes lenses and prisms work.
