In physics, when a ray of light is reflected back into, say, a lake or vessel of water, and is at a critical angle, the phenomenon occurs that the whole reflection is seen not just a partial one.
This critical angle on a water/air surface is normally 48.5 degrees, depending to some extent upon wavelength and therefore colour. It is the angle of incidence, the total internal reflection occurring above it.
Total internal reflection - When light strikes the boundary of a medium with a lower refractive index at an angle so great that there is no refracted rays occurs
