- A plane mirror is a mirror with a flat (planar) reflective surface. For light rays striking a plane mirror, the angle of reflection equals the angle of incidence. - The angle of the incidence is the angle between the incident ray and the surface normal. - Mirrors are polished surfaces coated with mercury such that they reflect most of the light falling on them. - Based on the type of reflecting surface we can classify mirrors as concave, convex, or plane mirrors.