A light ray is a stream of light with the smallest
possible cross-sectional area. (Rays are theoretical constructs.)
The incident ray is defined as a ray approaching a surface.
The point of incidence is where the incident ray strikes a surface.
The normal is a construction line drawn perpendicular to the surface at the
point of incidence. The reflected ray is the portion of the incident ray that
leaves the surface at the point of incidence. The angle of incidence is the
angle between the incident ray and the normal. The angle of reflection is the
angle between the normal and the reflected ray.
The Laws of reflection:
- The angle of incidence is equal to the angle of reflection
- The incident ray, the normal, and the reflected ray are coplanar
Specular reflection (regular reflection) occurs when incident parallel rays
are also reflected parallel from a smooth surface. If the surface is rough (on
a microscopic level), parallel incident rays are no longer parallel when
reflected. This results in diffuse reflection (irregular reflection).
The laws of reflection apply to diffuse reflection. The irregular surface can be
considered to be made up of a large number of small planar reflecting surfaces
positioned at slightly different angles. Indirect (or diffuse) lighting
produces soft shadows. It produces less eye strain than harsher, direct
The applet below illustrates how reflection and refraction takes place
in common substances such as water, vacuum, air, glass, and even diamond.