Stand-in for lighting setups while main actor rests — saves talent hours under hot lights. Must match approximate height and skin tone.
While you're adjusting the lights, your lead actor isn't sitting under the hot spots — instead, a light double stands in their place. This person must resemble the later protagonist in size, skin tone, and hair texture so that your light readings are accurate. It's not about identical facial expressions or movement sequences, but purely about ensuring light falls the same and shadows form the same.
In practice, this saves you hours — especially with complex setups involving multiple cameras or when shooting at night and every key light change needs to be readjusted. The star is in the dressing room, getting makeup, drinking coffee. Your light double patiently stands under the 10K, waiting. You look through the camera, fine-tune the lights, check highlights in the hair, control the fall of shadows under the eyes. As soon as everything is right, the double disappears, the actor comes in, and you have 20 minutes to shoot instead of two hours of setup.
Important: A light double is not your stand-in for movement sequences or camera positioning — that's a separate task. It's purely about the light. Therefore, your light double can also stand completely still; they just need to hold their head in the correct position and not frown. Good light doubles are experienced at holding absolutely still and understanding what your eye is drawn to. Some cinematographers work with the same light double for several weeks — they then know the lighting and already anticipate where it's going.
Practical tip from set life: Have your light double wear similar clothing to what the actor will wear in the scene. Light vs. dark fabrics cast different reflections. For close-ups of the face, you also need to pay attention to the same makeup foundation, otherwise you'll be measuring light values on a different skin surface. And: If your star will later be shooting with a wig, put the wig on the double too — the head outline changes, light breaks differently.