What characteristic distinguishes key light from other lighting types?

The key light is recognized as the primary source of illumination in a lighting setup, and it plays a fundamental role in establishing the mood, depth, and texture of a scene. This light is typically placed to create the most significant contrast and definition on the subject, making it distinct from other lighting types, such as fill lights or backlights, which serve supplementary roles.

In most lighting designs, the key light is strategically positioned to enhance the form and features of the subject, and its intensity is usually stronger than that of secondary lights. This attribute makes it the focal point of the lighting arrangement, as it shapes the visual narrative and guides the audience's attention.