One of the great things about this setup is that you really only need one light to create a high quality, dramatic portrait. Position this key light to one side of your subject so that it’s exactly 90 degrees to one side. Take a look at the diagram below to see where to position the key light. You can put a light modifier on this light if you want to, but this technique works equally well with a soft or a hard light source. With the modeling light on or by taking a few frames, make sure that the line between light and dark runs directly down the center of your model’s face, right down the tip of the nose. The model should be looking directly at the camera. And that’s it, you’ve created a split lit portrait!
You may decide now to spice up the shot with a hair light. Go right ahead, position one one the same side as the key light but closer to the background. This will create some separation between the model and the background.