The key light is the primary light source and usually the most important light that a, cinematographer, gaffer, or other scene illuminator will use in a lighting setup. The purpose of the key light is to light the form and dimension of the subject. The key light can be a hard or soft, and come from any direction and placed at different angles relative to the subject. The key light can be placed high or low producing different effects. But mostly the key should be placed in position that best helps tell the story.