The Background Light

THE BACKGROUND LIGHT

by William Lulow

It is often important, as we shall see, to speak of the background separately from the subject. Most good lighting setups almost always treat the background as one subject and the main subject as another. If we get used to thinking in these terms, lighting setups will be easier to conceive.

Usually, the background needs to be lit evenly for specific effects, so two lights are most often required They should generally be of equal intensities, otherwise the background will be unevenly lit. Background lights are placed behind the subject and aimed at the background only! The intensities of these lights will determine how bright or dark the background will appear on film, relative to the intensity of the main light of course.

Here are two shots taken with the same background. In the first, light from two accent lights was allowed to spill on to the background. In the second, these lights were turned off.

Look at the difference in the tonality of the background. A normal gray background could be made to appear anywhere from white to black depending on the position and intensity of the background lights.

 The main reason for lighting any background is that it is much further away from the MAIN LIGHT than is the subject. Light conforms to a law of physics called the “Inverse Square Law.” It basically says that the intensity of light falling on a subject varies inversely as the square of the distance between the light and the subject. This simply means that if a subject is twice the distance from a light, it will receive half the light’s intensity. This explains why backgrounds lit from any on-camera flash are usually black. Here is an example:

This image was lit with an on-camera flash. The subject is lit correctly, but the background is dead black. The light from the camera just isn’t strong enough to light any of the background.

 So, the solution to this problem is that the background has to be lit separately. Here’s an example:

This image was shot at the same backyard party, but an extra light was added to light the people in the background. In addition, a second light was taken off the camera and added to the foreground table as well. There was no “on-camera” light used.  

Here is yet another example:

This image was made with one light on the camera and another light set up to light just the five people by the window.

This image was made with the light on the camera turned off. 

So here, the foreground is in shadow while the background remains lit, thus attracting the viewer’s eye to the background instead. You can achieve these kinds of results by thinking of the background as being separate from the subject.

Here is another example:

This image was made by using a white background and lighting it evenly from both sides of the set behind the subject. This is sometimes referred to as “high-key” lighting. Everything looks bright.

This shot was made with a gray background with no light on it at all.

So, from these examples, one can readily see the need to think of the background as a different subject from the main subject you are shooting. This will help you in natural light situations as well. You need to remember that it’s always the “light-to-subject” distance that determines what kind of picture you are making and what you want to be visible in the photograph.