The Gaffer (gaffer definition) (Chief Lighting Technician) is the Lighting Technician on a film set that is responsible for the execution of the cinematographer’s lighting plan. He or she works directly with the cinematographer and runs the lighting crew to achieve the look of the film the DOP is going for. Being the gaffer is not a job to take lightly and all gaffers should strive to always be learning and on top of the latest equipment and technology.
Both on and off the set, the Gaffer or Chief Lighting Technician is one of the most important positions around. Though the average movie goer most likely has no idea the job even exists, they probably don't know what 99% of the other crew is/does either.
From the time a DP signs on to a project, the race begins to bring on all the preferred crew, arrange and determine all of the lighting needs for the film including day shoots, night shoots, generator (power) needs as well as any specialty lighting gags and much more. This work is generally finished in a short amount of time as most low-budget feature films, short films, music videos, etc. are given very slim to no prep time. Having a strong relationship with the cinematographer is vital at this stage.
It is a very stressful and difficult job, but is also extremely gratifying and can pay very, very well. Run the Lighting Crew. With help from the best boy you run the rest of the lighting technicians to run power, set lights and pre-light up and coming scenes and/or sets. All in a day work.