These senior photos were timed to allow beautiful backlighting on the subject. In order to get the proper exposure in the front also, a flash of light was also used to make sure the lighting is even and consistent across the entire frame. If you look into her eyes, you will see the flash (also called a "catch light"). The catch light is from an octagon shaped box to make it look more natural. It is used to keep the front of her lit and decreases shadows and imperfections that would have to be removed in post processing.