Law of reflection

Statement

The angle of reflection equals the angle of incidence (i' = i); incident ray, reflected ray, and normal at the contact point all lie in the same plane.

Why is it true?

For a plane mirror this makes the image of every light point symmetric across the mirror — the origin of the term "virtual image".

On a rough surface each microscopic point still follows the law, but the normals point in all directions → diffuse scattering instead of an image.

Applications

Plane and spherical mirrors, periscopes, optical-fiber routing, concentrated-solar reflectors, lidar and 3D cameras.

Topics that use this theorem

Related theorems

Step-by-step proofs