How to Position Lights for a Professional-Looking Portrait
Position a fill light.
The fill light helps balance your portrait lighting and creates a sense of depth to your image. Used properly, it can also create a moody or romantic image through the carefully controlled play of shadows. This light fills in the shadow areas created by the main light, as you can see in this figure. Position your fill light roughly the same height as your main light and give the fill light some kind of modification (via an umbrella or a soft box).