A
light ray is a stream of light with the smallestpossible 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 thepoint of incidence. The
reflected ray is the portion of the incident ray thatleaves the surface at the point of incidence. The
angle of incidence is theangle between the incident ray and the normal. The
angle of reflection is theangle 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 raysare also reflected parallel from a smooth surface. If the surface is rough (ona microscopic level), parallel incident rays are no longer parallel whenreflected. This results in
diffuse reflection (
irregular reflection).The laws of reflection apply to diffuse reflection. The irregular surface can beconsidered to be made up of a large number of small planar reflecting surfacespositioned at slightly different angles. Indirect (or diffuse) lightingproduces soft shadows. It produces less eye strain than harsher, directlighting.
The applet below illustrates how reflection and refraction takes placein common substances such as water, vacuum, air, glass, and even diamond.