Background Light
by William Lulow
I have written a lot about the background light. 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 when you are using a flash-on-camera setup, say, it really only is strong enough to light your main subject. It won’t be strong enough to light the background as well 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. Here’s an example of what I mean:
This was a typical flash-on-camera “grab” shot where I didn’t really have time to light the background. So, you can see that it came out dead black!
Here is another example where I purposely put some light on the background:
This image was shot at the same party, in the same backyard. This time I added an extra flash on a light stand to throw some light on the table in the rear of the photograph.
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. So, if you want to render a white background as white, you must light it separately from the subject.
Here’s another example of what I mean:
Here is a studio setup I did for some corporate portraits, some of which had to be full-length shots. If you look closely, you can see my background lights behind to the two black shades on either side of the no-seam. If they weren’t there, the umbrella and softbox would not have provided enough light for the background and, given the length of no-seam I needed, the background would probably have actually been BLACK!
This image was made with my iPhone with just the room light. You can already notice that the background is going gray.
Here’s an example of one of the images from this shoot:
Notice the difference in background tone! This one is really pure white. In order to reproduce the background as white, you need to make sure that it is at least one f/stop more than your main light.
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 on 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.
They were also then filtered with a haze filter over the lens that increased the effect of the flare.
The take-away here is that in order to control the tone of your background it has to be lit separately from your subject. If you treat your background as a subject in itself, you can readily see how to reproduce it just about any tone you wish!
