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Law of reflection (click to enlarge)

Reflection is the return by a surface of some of the light which falls on that surface. (Other parts get absorbed or refracted).

There are two main laws (called "the laws of reflection") that play a role in this:

  1. The angle of reflection of a ray (r) of light is equal to the angle of the ray of incidence (i).
  2. The incident ray (I), the reflected ray (R) and the normal (NO) all lie in the same plane. In this case it is the plane of your computer monitor.

The angle of incidence (ION) and the angle of reflection (NOR) are both measured by reference to an imaginary line called the normal (NO), which is perpendicular to the reflecting surface (HP), at the point of incidence (O). The point of incidence is the point at which the incident ray strikes the reflecting surface.

Understanding these basic principles are important in order to understand the many gemological terms that are used to describe optical effects caused by reflection.

Amongst those effects are: