A film set gaffer is a chief electrician on a film production crew who is responsible for the lighting of a film set. Here is an outline of the typical duties and responsibilities of a film set gaffer:

1. Planning and collaboration: The gaffer works closely with the director of photography, production designer, and other key crew members to plan the lighting design for each scene, taking into consideration the desired mood, tone, and camera angles.

2. Equipment preparation: The gaffer is responsible for preparing, maintaining, and managing all of the lighting and electrical equipment on set. This may include setting up and adjusting lights, rigging equipment, and running cables and power sources.

3. On-set supervision: During filming, the gaffer supervises a team of electricians and grips who assist in setting up and adjusting lights and equipment as needed. They work closely with the director of photography to ensure that the lighting is consistent with the overall vision for the film.

4. Troubleshooting: The gaffer must be able to quickly identify and solve any problems that arise with the lighting equipment, such as flickering or dimming lights, blown fuses, or other electrical issues.

5. Safety: The gaffer is responsible for ensuring that all electrical equipment and wiring on set is properly installed, grounded, and safe for use. They must also ensure that all crew members are trained in proper safety protocols for working with electricity and lighting equipment.

6. Record keeping: The gaffer maintains a log of all lighting setups and equipment used for each scene, to ensure consistency and efficiency during the production process.

In short, the film set gaffer plays a critical role in creating the visual style and atmosphere of a film through the use of lighting and electrical equipment, and must be highly skilled in technical and creative aspects of lighting design, as well as managing a team and ensuring safety on set.