The key light is the main source of light employed to illuminate a person or object on a television set. Typically, sets employ a Fresnel light (pronounced fray-NELL). The Fresnel features a spherical reflector in the back and a lens that focuses the dispersion of light--the Fresnel lens was originally developed for lighthouses. The key light usually illuminates from the direction the actor is looking.
The fill light is often filtered through a diffusing material, an acrylic plastic that looks like a shower curtain. The key light throws shadows, and the fill light smooths them out so that there are no dramatic differences between the bright side of an actor's face and the dark side.
The kicker light visually separates the actor from the set's back wall. If the figure has dark hair, say, and the wall behind her is dark, the hair will seem to blend in with the wall. The kicker is usually put on the opposite side of the shot from the key light. The kicker light is usually a Fresnel, but it could be any of a variety of lighting instruments, including a simple bare light bulb. Lighting technicians take great care to position the kicker to avoid lens flare-- unwanted bursts of light that show up on video as star bursts, rings or circles and obliterate the image.
Television lighting is separated into three general categories.
High key: The entire set and the actors are evenly lit and there is low contrast, meaning no, or few, shadows. This style of lighting is mostly used in comedies.
Low key: This style employs a lot of areas in shadow and is punctuated with some more brightly lit areas. Low-key lighting is most often used in dramas.
Graduated tonality: This technique use soft, even light to produce weak shadows and gradated grays. A variety of techniques produce artificial shadows, including painting them onto sets.
Unlike film, video does not require that you use a light meter to ensure that your images will come out looking good. In general, if it looks good on the monitor, your lighting is doing its job.
If you use too much ligh,t your images will look too flat. If underexposed, video looks like old grainy film. The scratch effects you'll see are called "noise."
When video is over-exposed, the image will "white-out," which is otherwise known as "clipping." This is usually as bad as under-exposing.
Flat images occur when the key light and fill light are too close in intensity. The key light should be two to three times brighter than the fill light.
Remember, lighting a set takes a lot longer than you might think. Allow plenty of time to position your lights in a way that will eliminate harsh shadows.
Lights get very hot, so wear leather gloves when handling them. Cotton gloves will burn through. Also, be careful when plugging in lights to make sure the light doesn't require more amperage than the power source will provide. That will trip the circuit breaker or could start an electrical fire.
These days, television frequently uses either LED or fluorescent equipment. The old tungsten lights, which were the mainstay of earlier television lighting and are still used today, are inefficient. Only 10 percent of the energy they consume is used to create light--the other 90 percent is emitted as heat. Fluorescent and LED lamps are close to 100 percent efficient and do not emit nearly as much heat on the set.