What is the purpose of lighting? How does a filmmaker or photographer decide that a light should go here rather than over there? Fundamentally, lighting is about directing the eye of the viewer. The frame will include a variety of elements; the lighting will determine which ones the viewer will look at. In general, the human eye is attracted to light, so a bright face against a dark background will immediately draw the viewer's eye. The exception to this is in a case where the frame is overwhelmingly light, with only a small dark area. In this case, (as in Richard Avedon's photographs), the viewer's eye is drawn to the "exception" in the frame--that is, the dark element.
There are an endless number of ways to set up lights, but the most basic and important one is called three-point lighting. As shown in the diagram at right, there are FOUR key elements in this setup: the key light, the fill light, the backlight, and the camera. The key light is the strongest of the three lights, and it determines the primary direction of the light in the shot. (The effect of different key light placements will be discussed further in Section 3.) The fill light is used to diffuse the strong shadows thrown by the key, and is often placed 90 degrees away from the key light. The backlight is used to give the subject a bright "edge" of light to separate it from the background, and is often placed 180 degrees from the fill light. The camera and key light are generally positioned first, and the fill and backlight are arranged later. Modern upbeat comedies offer some of the clearest examples of three-point lighting. Next time you're watching, say, "Knocked Up," pause the film and look carefully at how the characters are lit. In virtually any shot you can identify the light from the key, the fill, and the backlight. While a major motion picture will often use dozens of lights for a given shot, the basic tenets of lighting hold true.
Lighting is central in creating the mood of a shot or photograph. The last section discussed comedy lighting. This kind of lighting is almost always bright (creating an upbeat mood), simple, (so the audience is focused on the jokes and not the lighting scheme), and high-key. High-key means that the key light is above the faces of the actors and shines down on them. This mimics the angle of the sun and seems natural to the audience. The opposite is low-key lighting, where the key light is placed below the faces of the actors and shines up at them. This creates unnatural and scary shadows on the faces of the actors. (Think of when you hold a flashlight under your chin while telling a ghost story at a campfire.)
To compare with comedy lighting, think of the lighting in a suspense or horror film. ("Touch of Evil" offers many examples of great, scary lighting.) In contrast to comedy it is usually dark, with deep shadows covering much of the frame and often parts of the actors' faces. Additionally, it is often complex, drawing the viewer in to examine the entire frame or even forcing the viewer to question which element in the frame is most important. (Is the villain about to come through that door over there, or is the hero about to find the evidence in the desk?) This uncertainty on the part of the viewer creates dramatic tension that can be employed to great effect.
There are thousands of lighting setups to explore, but with an understanding of three-point lighting and the contrasting effects of bright/dark, simple/complex, and high-key/low-key, you are well on your way to creating interesting and powerful images.
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