The Four Classic Lighting Patterns: Butterfly, Loop, Rembrandt,
There are four basic or classic lighting set-ups. The terms refer to the shadow created by the main or “key” light. In order to reduce the severity of shadows, there is often a fill light for the shadows, and a rim or hair light to help separate the model from the background. I’ve ordered the light patterns here:
Butterfly: the light is “on axis” with the camera, typically slightly above the camera at a 15 to 30 degree angle, but also right around the lens as circle light.
Rembrandt: now the light is 45-75 degrees to the side. The shadow of the nose merges with the shadow of the cheek, creating a small triangle on the cheekbone. Often the far side eye is in darkness.
A little deeper into the classic light patterns: Usually, the fill light is on axis for loop and Rembrandt lighting. This allows for the most natural look. Move the fill light to the side and it becomes more dramatic.
This image is from a runway event using natural light. She has a bank of windows camera right acting as the key light, and there's another set of windows behind me creating gradual shading on the left side of her face.
If this is new to you, set up your lights and practice. See where the shadow falls. Each face is different-- the height of the cheekbones and the depth of the eye sockets are huge factors in where, exactly, you can position the light. Remember, you want to see a catch light in the eyes (preferably both eyes).