Lighting The Background

by William Lulow

Many amateur photographers who don’t take the trouble to study lighting simply “pop-up” their camera’s built-in flash when they think they need more light on a particular subject. This may be fine for snapshots, but it simply won’t cut it for more professional type shots. There are a couple of basic “laws” of light that one needs to study, however, if success in creating good photographs is the goal.

  1. Light travels in straight, parallel lines from the light source to the subject.
  2. The intensity of the light falls off geometrically when the lamp-to-subject distance is increased. In other words, the farther away the light is, the weaker it will be. Usually, less light produces images that are difficult to see.
  3. Modern electronic flash units – speedlights, are the portable kinds of flash units that you can attach to your camera. Built-in flash units are ones that come with the camera. Both will usually create enough light to make a decent picture, but their  relative power will decrease rapidly when the flash-to-subject distance is increased. Therefore, if your subject is more than 20 feet away, the camera’s built-in flash won’t help much, given the same exposure. A stronger flash, one that puts out more power will work much better.
  4. Most speedlights have automatic sensors built in to them that measure the distance from the flash to the subject, usually by sending out an infra-red beam which hits the subject and bounces back to the flash unit. The flash output is then controlled by a series of thyristors which regulate the flash’s intensity.
  5. This produces enough light to make an image, but doesn’t add much to the overall quality of the picture.

If you are using any type of artificial lighting, the one law that determines the correct exposure for the image is the “LAMP-TO-SUBJECT DISTANCE.” You can verify this by using a light meter and a photoflood bulb. If you place your meter 5 feet from the lamp and get a reading of f/8, say, moving the meter to 10 feet will result in a one f/stop more exposure or f/5.6. The light will be half as bright, requiring the additional exposure. In the days before sophisticated electronic cameras and light meters, studio photographers would often use this method to measure their lamp-to-subject distances and consequently their exposures in f/stops. Richard Avedon, one of the most famous photographers of the twentieth century, used a rope with knots tied to it at different lamp-to-subject distances indicating the various f/stops needed, all arrived at by the above method. The closer knots would be for f/stops around f/16 and f/22, and as the knots were farther away from the light they would indicate f/8, f/5.6, etc. Avedon favored large view cameras that used 8×10″ and 4×5″ film sheets. These cameras also used relatively “slow” lenses which often had a maximum aperture of f/5.6. So this method assured him of correct exposures in the studio setting without having to use his light meter every time. Photographers could also use the same method to measure the effect of light on their backgrounds as well.

But what do modern photographers do when they wish to control the tone or exposure of the background in their images? Flash units that are part of the camera or are mounted on the camera have only very limited range. If you adjust your exposure so that the background will be light enough to see, chances are, your foreground will wind up being overexposed.

Here’s an image where the people in the middle were correctly exposed but the woman on the right, closer to the camera, was somewhat washed out. No amount of exposure compensation can correct this problem. If you wanted this image to be correctly exposed, you would have had to place a second light to light the women in the middle and then corrected the exposure for the woman in the foreground.

Here’s an example of how I might use a second light source to illuminate the background:

You can actually see the position of the second light, and there was actually a third light, set up to the left of the speaker. Here, I wanted to silhouette the cameraman in the foreground, so I simply turned off, the light on the camera. Had I just used the light on the camera and no other lights, the cameraman would have been lit correctly but the speaker would have been dark due to the distance between my on-camera light and the subject.

Making images like these work is all about realizing that backgrounds need to be lit separately when working with any type of artificial light source. With this technique, I can choose whether or not to silhouette the foreground or add detail to it simply by turning off one of my lights.

Here is a simple looking shot with a white background:

In order to render this background pure white, it had to be lit separately from the subject. It also had to be at least one f/stop brighter than the main light. Here is a diagram of the lighting setup I used:

Without lighting this background it would have reproduced a grayish tone. The takeaway here is that the background should always be considered as a separate subject and lit accordingly. That is the only way you will be able to control whether it is light or dark, or rendered a color you want it to be.

Here is another example of lighting the background:

I used two lights bounced into umbrellas to light the people and a third light, with no umbrella, aimed straight at the rear of the airplane in order to light the background. Without this third light, the people would have been standing in front of a black background with very little, if any detail.

If you want to give some sense of place or render the background a certain tone, you must light it separately from the main subject.