Every incandescent light needs to be fine-tuned to have the
best results. Usually, it carries its very own light housing that incorporates
some kind of reflector behind the lamp. This is partly to make use of all the
light radiated and partly to control the beam. Green
screen background the deeper and more concave the reflector, the more
concentrated the beam as it is harder to spread a beam that is already tight
when it leaves the housing compared to concentrate a broad beam. The most
general-purpose housing has reflectors that give a spread of between about 45
and 90 degrees. Light that gives tighter concentration is intended for more
specialized use. Many housing allow some change to the beam pattern by moving
the lamp in and out of the reflector or by moving reflector doors. Barn doors
fitted to some housing have a slightly different effect: they cut the edges of
the beam rather than concentrate it. The beam patterns from most housings show
a fall-off from the center outwards; even with a well-designed reflector, there
is still a powerful concentration of light in the lamp’s filament. One way of
reducing this fall-off in the design of the housing is to cover the lamp from
direct view with a bar or a spiller cap. If the reflector dish is big as well,
the result is a degree of diffusion. Even softer but less intense light is
possible if the inside of the dish is finished in white rather than bright
metal.
