Prism shaped pavement light redirecting sunlight through total internal reflection. Credit: glassian.org In the beginning, vault covers used round plano-convex lenses or even just flat glasses.

The incident ray is refracted towards the normal as it enters the glass prism from air. It is then refracted away from the normal at the boundary between glass and air as it leaves the prism.

They reflect off the rear face ... This means that the light leaving the prism is spread out into its different colours, a process called dispersion. This experiment is recorded as first being ...