Stand-ins in
film are often misunderstood to be
doubles[?] for the actors, that is, people who double for the actor during filming, e.g. from behind, in makeup, or during some dangerous stunts. Stand-ins are not the same as doubles, and do not appear on camera. Stand-ins are people who stand in for the actor
before filming, while the lighting is set up. Lighting setups on a film can be a slow and tedious process; during this time the actor will often be on the sidelines watching the setup, or somewhere else studying his or her lines.
Stand-ins must not necessarily look like the actor, but they must be the same height and build as the actor so that the lighting in a scene will be set up correctly (for instance, if the lighting is set up with a stand-in shorter than an actor, the actor will have his head in relative darkness).