Amps, circuits, and why a gaffer does math before anything gets plugged in
Introduction
Every lighting fixture on a set draws current from somewhere, and figuring out where that current comes from, how much of it is available, and how it’s safely split across circuits is its own skill, usually the job of the gaffer and the electric department rather than the camera team. Overloading a circuit isn’t a minor inconvenience; it can trip a breaker mid-take, damage equipment, or start a fire, which is why power distribution gets planned as carefully as the lighting design itself.
Practicals and Space Lights
Not every light on set is a dedicated fixture. A practical is any light source that appears in the frame doing double duty as set dressing, a lamp, a neon sign, a window fixture, sometimes swapped for a higher-output bulb to actually contribute usable light rather than just looking good on camera. A space light is a large, soft, balloon-like or open fixture hung overhead to fill a big area with soft, even light, often used to bathe an entire set in soft ambient fill rather than lighting anything directly.
Amperage and Circuit Math
Every fixture has a power draw rated in watts, and every circuit or generator output has a maximum safe current rated in amps. Converting between the two (watts divided by voltage equals amps) is basic but essential math for anyone distributing power on set, since plugging too many high-draw fixtures into a single circuit is exactly how a breaker trips mid-take. On a small shoot this might mean checking how many practical household circuits a location can safely offer; on a larger production it usually means bringing in a generator and a dedicated distribution package built for the day’s lighting plan.
Generators and Distro
Bigger productions, especially exterior and location shoots without reliable building power, bring in their own generator along with a distribution (distro) system: cable, boxes, and breakers that split the generator’s output into safe, manageable circuits feeding each lighting position. Building this out correctly means balancing loads across phases (on three-phase generators), leaving headroom rather than running circuits at their absolute maximum, and running cable safely so it isn’t a trip hazard or exposed to weather and foot traffic.
Why This Matters to Non-Electricians
Even camera and production crew who never touch a distro box benefit from a basic grasp of this: knowing why a location’s power might not support the lighting plan, why a generator is booked for a day that otherwise looks simple, or why swapping in one more HMI isn’t as trivial as it sounds. It’s the kind of infrastructure work that’s invisible when it goes right and disastrous when it doesn’t.
Conclusion
Power distribution doesn’t show up on screen, but it’s what keeps everything that does show up on screen actually running. Understanding amperage, circuit limits, and how practicals and space lights fit into a lighting plan is a foundational, if unglamorous, part of how a lighting department actually does its job.