Position[edit]

The key light can be "hard" (focused) or "soft" (diffused), and depending on the desired setup can be placed at different angles relative to the subject. When part of the most common setup—three-point lighting—the key light is placed at a 30–60° angle (with the camera marking 0 degrees). In addition to the horizontal angle, the key light can be placed high or low producing different effects. The most common vertical position for the key light is at a 30° degree angle (i.e. slightly above the eye line; the nose should not cast a shadow on the lips).
A key light positioned low appears to distort the actor's features, since most natural or ambient light is normally overhead. A dramatic effect used in horror or comedy cinematography is a key light illuminating the face from below. A high key light will result in more prominent cheek bones and long nose shadows. Marlene Dietrich was famous for demanding that her key light be placed high.
Lighting a scene[edit]

Using just a key light results in a high-contrast scene, especially if the background is not illuminated. A fill light decreases contrast and adds more details to the dark areas of an image. An alternative to the fill light is to reflect existing light or to illuminate other objects in the scene (which in turn further illuminate the subject).
In addition to a key light, a back light may be added to "separate" the subject from the background. When the subject and/or camera are moving or turning