Lighting (Kathy)

Three point lighting is a technique commonly used in films, adverts photos etc. It creates a sense of depth on people by making them look 3D.
It is made up of 3 lights (suprisingly) one placed behind the subject and the other two at 45 degree angle roughly on each side.

KEY lighting- primary to illuminate a subject positioned at 15-45 degree from one side of the camera and down by about the same so its above the subject. This represents the primary source of light stimulating the sun, a window, a light bulb etc.

FILL lighting- after the key light is positioned there is a shadow on one side of the subject. The fill is meant to reduce this and should be placed opposite the key light but needs to be half the brightness and must not be at the same angle otherwise it will look unnatural.

BACK lighting- this is placed behind the subject opposite the camera, but at a higher angle to avoid the light shining straight at the camera lense. It creates a glow on the back of the subject and separates them from the backround. It also prevents te subject from looking 2D, it is also known as the "hallo effect"

Mood
For a comedy- turn up fill to create a more evenly lit set, and a jolly atmosphere
Dramatic- turn down fill to increase shadow and build up the suspense and tension

this is where i got the information http://filmstudies.suite101.com/article.cfm/threepoint_lighting