Lighting a scene for film is an integral part of the art of the medium. If done incorrectly, viewers will not see enough of the scene or see too much and not generate the desired emotional response. When done correctly, just enough information is conveyed and the viewer can attach an emotion to the image they are seeing. There are five basic types of lights that are commonly used to light a subject.
This is the main light on the subject and will generally be the brightest light in the scene. Together with a fill and backlight, this will make up the basics of three-point lighting. The key light is generally placed in front of the subject and off to the side. You can vary the appearance of the key by making it a spotlight, which will create a hard key with definitive shadows, or flooding it for a soft key with less shadows.
The fill light is used to fill in the dark spots that the key light creates. It is placed on the opposite side of the subject as the key light and is generally a less intense light. Also, the fill should be more of a flood light for a softer light than the key.
This light is placed in back of the subject to light it from the rear. This will provide a light ring on the edges of the subject, which will separate it from the background and add more dimension to the framing.
A background light can be used to light the background of the subject. It is generally placed behind the subject and aimed towards the background of the scene. This type of lighting can be useful in illuminating the background of a dark scene for added depth.
Practical lights are lights that can be seen within the scene. Examples include lamps and other lighting decorations that will be in the shot. These lights can double as decorations as well as sources for the light in your scene. Practical lights will also inform the direction of the lighting of your scene.