The main light is the source of illumination for a picture. It’s the one that’s measured for exposure with an incident meter. Using one is explained in the Photofocus post Exposure Tactics: Incident Metering. It sets the mood for the photograph. It’s the one that all the other lights serve. It also provides the main diffused highlight in a portrait. It’s important. The question I get asked most often about it is “How do you know where to put the main light?” That’s a good question. A really good question. The answer? It comes down to symmetry.
Faces are not symmetrical in about ninety-eight percent of the world’s people. These faces’ sides are different. One eye will be larger than the other, same for the nostrils, cheeks and even the width of each side will be different. These traits add character and interest. They also tell where to put the source of light.
Thick or thin?
Study this photo of Shawn for a half a minute or so. Shawn is a handsome, engaging man, no doubt. Let’s take a close look at the asymmetry that makes him look so distinguished. His right eye is smaller than his left. His right nostril is larger than his left. So is his right ear. His right side is thinner than his left. Seeing what I’m saying about the thin and thick sides isn’t easy so you might just want to take my word for which one is which. Don’t.
Here is a super easy way to see this difference. Open a portrait where the subject is looking head on into the camera, one like Shawn is doing in the photo above. Use Photoshop to cut the face right down the middle. Duplicate each side and use Free Transform to flip it horizontally. Put the same sides together and the difference is easily seen as shown below.
That example makes it instantly clear which side is the thin one. Let’s look at another one. In the next photo, of Karen, which side looks thinner? The answer is below. Before peeking, look carefully and make a pick… her left or her right? Here’s a hint: There’s a reason her hair is parted on the left to cover part of her right.
The Three Versions: Normal, Thin & Thick
Light the Thin Side…
It’s almost as if Yoda were whispering the wisdom of light. Placing the source of light on the thin side puts the thicker side into shadow which makes that side less noticeable. Women with long hair will more often than not part their hair so it covers the thicker side of their face. I have asked lots of my lady clients why they wear their hair as they do. The answer is always “It looks better.” Covering the thicker side of the face with hair and / or minimizing it with shadow makes a face more symmetrical.
By the way, there’s a technical name for the two percent of the population that have truly symmetrical faces. It’s “super model.”