Complete reflection of a ray of light in a medium such as water or glass, from the surrounding surfaces back into the medium.
It occurs when the angle of incidence is greater than a certain limiting angle, called the critical angle. In general, it takes place at the boundary between two transparent media when a ray of light in a medium of higher index of refraction approaches another medium of lower index of refraction at more than the critical angle. At all angles less than the critical angle, both reflection and refraction occur. Total internal reflection is responsible for rainbow s, atmospheric halos, the sparkle of a diamond, and the path of light through optical fibres.