How bright is each light source?
Of the five elements of DICCH, intensity is the easiest to understand and, I’ll wager, the one given the least creative consideration. So, rather than think of a light source as being just bright or dim, think of it in terms of the many ways that its intensity can affect your shot.
A camera’s exposure settings (shutter speed, aperture, and ISO) are based largely on the overall intensity of the light in the scene. For any given amount of light, there are many combinations of shutter speed, aperture, and ISO that can be used (these are called equivalent exposures). These three camera settings work in opposite directions—meaning that if you change one to be bigger/faster, then you have to change another to be smaller/slower to keep the overall exposure the same. Once you know the basics, you’ll start to see the creative opportunities.
For instance, depth of field describes how much of your image appears to be in focus from front to back in the scene. A wide aperture, such as f/2.8, lets in lots of light and creates shallow depth of field. Conversely, a narrow aperture, such as f/22, only lets in a small amount of light and creates deep depth of field. So, if you don’t have much light intensity and you want to create deep depth of field, then you’ll have to use a slow shutter speed (which might cause camera shake) or a high ISO (which might cause digital noise in the image). If neither of these options works, then you’ll need to increase the intensity of the light.
If you have multiple light sources, then their intensities will affect the contrast in your image—which, as we’ll discuss in just a bit, is the difference between the bright and dark areas of your shot. Typically, contrast is created because the intensity of light is greater on one side of the subject than another. Put another way, if your image appears flat, then you can either reduce the intensity of light on one side or increase the intensity of light on the other to increase contrast. The contrast is increased because you are creating more shadows.
In Figure 1.7, I’ve arranged two lights, each placed at 45° to the left and right of Mallory, and set them so that they have the same power. As you can see, her face lacks shape—because it lacks shadows that reveal shape. Then, in Figure 1.8, I reduced the power on the left light so that it is one quarter as bright (i.e., I reduced it by two stops). Now, the lower intensity allows more shadowing and thereby shows more shape.
Figure 1.7. Here I have set two lights angled towards the subject from 45° on the right and left. They are the same distance away and set at the same power. The shot lacks shadows and depth because both sides of the model are lit equally. This is basically the same as shooting with your on-camera flash.
Figure 1.8. Dimming the light on the left by two stops allows more shadows to be created by the light on the right. Actually the shadows were there before. The camera could not see them because of the intensity of the light on the left.
If you are wondering how this is different than the photos in Figures 1.2 and 1.3, here I have used two lights. In Figures 1.2 and 1.3, I used a single light. What I want you to learn is that, when you are crafting shadows, the intensity of a light is as important as its position.