The most commonly used style of lighting in Hollywood movies is three-point lighting. This describes the light used on the subject. It is made up of the main key light, a fill light and a back light. The key light is the primary source of light. For example, outside, the direction of the sun dictates the key light. A fill light is most often a "cheat," or a light that makes the entire face of the subject visible. The back light is often called a "kicker" because it "kicks" the subject off the background. Most lighting styles are variations on this basic setup. One example is the broadside key, which creates a flatter look often used in comedies, where the key light hits the side of the subject facing toward the camera. The narrow side key creates a more dramatic effect when the key light hits the far side of the subject in relation to the camera. The exact positioning of the key light gives as many styles as there are places to put the camera.
Color temperature is a photography concept that became more important with the advent of color film and continuity editing. Color temperature represents the general color of the source of a light. For example, a light bulb burns at a color temperature of around 2,500 degrees Kelvin, which gives off an orange color. In contrast, the sun burns at about 6,500 degrees Kelvin, giving the sky a blue color. A hotter light burns bluer. This is critical for continuity editing, because the goal is to have all of the colors appear the same throughout the movie. Knowing the color temperature of a light is important to correct lighting.
There are three major types of lights used in movies: tungsten lights, HMIs (Hydrargyrum medium-arc iodide) and LEDs. Tungsten lights have many kinds of lenses and shapes to control them. Tungsten lights were by far the most popular until the invention of the HMI. HMIs use far less power than tungsten to put out the same amount of light. They create an electrical arc instead of using a filament, which also makes them last longer. The only drawback is that they aren't compatible with the 60-hz electricity used in most households because they create a flicker and require a certain kind of generator. They have a blue tint. The newest addition to the lighting family is the LED, or light-emitting diode. These lights have been around for a long time, but previously were not powerful enough to light a whole room. They typically burn blue.
There are several basic tools used in lighting. To change the color of a light, "gels" are used. Gels look like pieces of wax paper or plastic wrap attached to the front of the light. They are specifically tailored to give a certain effect. Usually, gels are attached using a "c-47," which is industry slang for a clothespin. There are conflicting reports about where that name came from, but "c-47s" are crucial on movie sets because of their many uses. The c-47s are attached to the "barn doors" of a light, the tool that allows for rough directional control of the light.