Background Light

Background Light

by William Lulow

There are so many things a photographer can do with the background in a photograph. It can be out of focus. It can be light, dark, any color you want. The background often lends the image a certain psychological tone. If it is light, then the feel of the picture is light also. Conversely, if it’s dark, so is the feeling. You can often mix things up for psychological effect. There are so many things you can do with your backgrounds. Usually, backgrounds serve to separate the subject from other things that may be in the room or even outdoors. A really soft background outdoors can almost act as a painted backdrop. But the main thing to know about any background in any photograph is that if you want it to show, you have to light it.

The reason for this is that if you are using any kind of artificial light, once it is aimed at a subject, the light rays will only travel that distance. We call it the “lamp-to-subject” distance. And, it is this distance that controls the exposure when you are using studio-type lights, be they hotlights or electronic flash. The exposure of the film or digital sensor, follows what is known as the “inverse square law.” This basically says that the intensity of the light (which creates the exposure) varies inversely with the square of the distance between lamp and subject. A simpler way to put this is that if you light something with an ordinary household light bulb, the brightness of that object is “x.” If you move that light twice the distance away, the effect of it’s strength will be half. So, if you are getting an exposure of f/11 on your subject and you double the distance between the light and the subject, the exposure would only register f/8. If you moved the light four times the distance back, the exposure would only be f/5.6. So each doubling of the distance further away from the subject reduces the exposure by 1/2 each time. From these examples it is easier to understand that a light bulb generates light that “falls off” dramatically the greater the distance from the subject. Here are a couple of images that illustrate this:

This is a setup for a job that required a white background for a series of headshots and full-length shots as well. You can see that it actually required four lights. Two to light the background and two for the subject and foreground. If the background wasn’t lit separately, it would have registered almost a dark gray tone due to the fall-off of light. Here’s the result:

The entire background registered white in the final shot. Here’s another example:

This series of images were shot with a white background and a white foam core piece behind the model to get a two-toned background. They were the same shade of white except the paper background was not lit and the white foam core picked up light from the main light because it was closer to the light. (You can tell the foam board was closer to the light because of the shadow cast.)

Now that I have talked a bit about light and how it behaves, the importance of the discussion is that the background needs to be illuminated somehow if you want it to show in your image. If there is enough ambient light in your scene, whatever is in the background will show because it’s the sun that’s lighting the whole scene. The sun, of course, is the only light in our solar system. The moon gives off light as well, but it is the reflection of sunlight. So, if you begin to use artificial light, you need to be aware of its properties. You can test this out by putting something on a piece of white background paper and lighting it with a single light source. Watch what happens. The pure white paper will reproduce as a gray tone in your picture. This is the reason that if you want a white background to reproduce as white, you have to light it. Given the proper amount of light, you can make a gray piece of paper reproduce as white, if you light it separately.

When you are shooting in the studio, or even on location with flash, the background needs to be lit by itself. If you remember that the flash only goes so far and it’s the lamp-to-background distance that determines what tone the background will be rendered. One example of this is that when you use a flash-on-camera, the subject will be lit, but the background will be black. Another example is, you might think that if you placed a subject against a white background and then set up an umbrella or other light to light it, that the subject and background would both be lit. In reality, the subject might receive the right amount of light, but the background would reproduce a shade of gray, not white. The reason for this is that the light from the flash “falls off” as the distance to the background increases, as I have explained above. So, if you want to render a white background as white, you must light it separately from the subject.

A few years ago, I was playing around with the concept of actually flooding the background with light. As a matter of fact, I wanted to light the background so much that the light would actually spill over to the subject. I saw that it began to produce an interesting kind of “flare.” I decided to see if I could exploit that flare for dramatic effect. These images were made with the background lights set at two to three stops greater than the main light. Both images were lit with two lights on the background and a large umbrella for a main light.

Then there are other “tricks” you can do with the background. Think of putting a light behind it and poking some holes in it:

Then you can also experiment with putting other lights in the background for other effects:

This was shot with a reflective, mylar background.

So, there are many different things you do with backgrounds. Just remember that they really need to be lit separately for best effect. You always need to consider what you want the background to look like and light it accordingly.