Almost all surfaces reflect a certain amount of the light which falls on them. The degree and type of
reflection
depends on how polished and smooth the surface is, and on its pigment makeup.
The Law of Reflection stipulates that the angle of
reflection
of a light ray from a reflective surface is equal to the angle of incidence of the light ray (i.e. the angle at which the ray hits the surface), but in the opposite direction. The angle of incidence of the light ray and its angle of
reflection
are measured between the light ray and a line perpendicular to the surface.
The amount of light reflected from a reflective surface is determined by its
reflection
factor, and the
pattern
of
reflection
depends on the finish of the surface. A polished mirror will reflect the light in a specific direction, while an unpolished surface reflects the rays of light at various different angles. When the surface of a
reflector
is flat, the rays which hit it are all reflected in the same direction in accordance with the law of reflection.
When the surface of a
reflector
is curved, (as in most reflectors used in theatrical luminaires), the angle of
reflection
will be determined by the curvature of the reflector. Theatrical luminaires use spherical, ellipsoidal, and parabolic reflectors, each of which has a characteristic
reflection
pattern. In the optical systems of theatrical luminaires, the principles of
reflection
are applied in reflectors, which are colorless mirror-like surfaces. Reflection also affects the perceived color of objects, depending on which wavelengths are reflected from the object and which absorbed. Dichroic filters and mirrors, too, apply these principles, reflecting the undesired wavelengths away.
Most luminaire reflectors are made of polished metal, although some luminaires or lamps have dichroic glass reflectors. Reflectors can be constructed of a continuous curved surface, or can be multi-faceted.
Multi-faceted metal reflectors are more efficient as each facet projects part of a larger, more efficient, reflector. Some reflectors are broken up into a mottled pattern, and produce a diffused light beam.
The quality and efficiency of the
reflector
is an important factor in the amount of light output a luminaire will have. The more light the
reflector
absorbs, the stronger the
lamp
output necessary to generate a strong light
beam
on the stage. A deteriorated
reflector
will absorb much more light than a new one, converting the light to heat instead of reflecting it.
