In three-point lighting, what is the purpose of the 'back light'?

The purpose of the back light in three-point lighting is to create separation between the subject and the background. By illuminating the subject from behind, the back light helps to highlight the edges of the subject, giving it depth and dimension. This technique creates a visual distinction that prevents the subject from merging into the background, enhancing the overall composition of the scene.

In three-point lighting, each light has a specific role: the key light provides the main illumination; the fill light reduces unwanted shadows created by the key light; and the back light adds a rim of light that separates the subject, enhancing its visibility against the background. This separation is crucial in ensuring the subject stands out and appears more three-dimensional, which is especially important in various applications like film, photography, and stage production.