In specular reflection a mirror surface reflects a beam of light so that the angle of reflection is equal to the angle of incidence (eg. the angle of the incoming light is the same as the angle of the outgoing/reflected light). The diagram shows how the incoming (incident) light is reflected off the mirror at the same angle to the perpendicular line (which in geometry is called the ‘normal’).
In a perfect reflection all the light will be reflected from the mirror surface. In real-life, non-perfect situations, the base material of the mirror and the surface of the mirror may:
- Absorb light: the light is absorbed (the energy of the light is taken up by the material).
- Imperfectly reflect light: The surface is an imperfect mirror and some of the light is scattered.
For the photographer, the way light behaves when it hits a surface is important. The degree to which light is reflected from any surface depends on how mirror-like it is. There is a continuum of reflective surface types from a perfect mirror (where specular reflection occurs) tending towards diffusion surfaces and absorbing surfaces. Specular reflection becomes less focussed as light is scattered on a surface that tends toward diffuse reflection. Specular reflection will continue but will become less intense as the surface absorbs light with an absorption surface. A surface may behave as both, a reflecting and absorbing surface. In reality many surfaces exhibit both behaviours.