20 Lighting Terms Producers Hear on Set, Explained

Gaffers talk fast, and when the clock is running nobody stops to define their terms. If you've ever nodded along to a conversation between a DP and a gaffer while quietly wondering what half of it meant, this is for you. Knowing the language won't make you a lighting technician, but it will help you follow decisions, spot potential delays early, and ask the right questions before they become problems.

Power and distribution

1. Generator (or genny) A diesel-powered unit that supplies electricity on location. Size is measured in kilowatts (kW) or kilovolt-amperes (kVA). A small interview shoot might run on a 20 kW unit; a large exterior commercial can need 250 kW or more. Generator choice affects truck size, fuel cost, noise levels, and whether you need a licensed operator on site.

2. Distro (distribution) The cable and board system that takes power from the generator and breaks it into individual circuits for lights and other equipment. Good distro layout keeps cable runs short and safe. Poor distro is one of the most common causes of unexpected delays at the start of a shoot day.

3. Tie-in Connecting to a building's mains supply instead of a generator. Cheaper to run, but requires an electrician to assess available amperage, and building management approval. Tie-ins can fail if the building's supply is weaker than expected — worth confirming early.

4. Load (or electrical load) The total draw of all lights and equipment running at once, measured in amps or kW. The gaffer tracks load continuously to avoid tripping circuits or overloading the generator. If you're adding equipment late in prep — a large LED wall, for instance — tell the gaffer so the load can be recalculated.

The lights themselves

5. HMI A daylight-balanced globe that produces a lot of output for its size. Common for exterior work, car shoots, and anything that needs to match or overpower sunlight. HMIs need a ballast to run and take a few minutes to warm up and restrike if switched off — relevant when you're planning turnarounds.

6. LED Now the dominant fixture type. Energy-efficient, runs cool, often battery-capable, and many units are colour-tuneable. Output and quality vary enormously between fixture types. "LED" is not a single thing — a small on-camera LED panel and a 100 kW LED soft source are entirely different propositions.

7. Tungsten Traditional incandescent fixtures. Warm colour temperature, simple to use, relatively inexpensive to hire. Increasingly replaced by LED but still used where their particular quality of light suits the look. They run hot and draw significant power.

8. Practical Any light that appears in frame and is meant to look like it belongs in the scene — a bedside lamp, a neon sign, a desk light. Practicals are often swapped for higher-output globes or dimmed to sit correctly in the exposure. They're a set-dressing and lighting-department conversation simultaneously.

Shaping and controlling light

9. Diffusion Material placed in front of a light source to soften and spread it. Comes in rolls or frames, in varying densities. More diffusion means softer shadows and a gentler look; it also costs you output, which may mean moving to a larger fixture or supplementing with another source.

10. Flag A rectangular panel, usually black, used to block light from hitting the lens or spilling where it isn't wanted. Flags are on arms attached to stands. Knocking one over mid-take is a common on-set interruption — which is why good rigging discipline matters.

11. Bounce Reflecting light off a white or silver surface rather than pointing it directly at the subject. Bounced light is soft, flattering, and uses the same fixture to cover a wider area. On exteriors, large bounce frames can act as a key light without any electrical power at all.

12. Negative fill Placing a black surface opposite the key light to absorb light rather than reflect it. This increases contrast and shadow depth. When a DP asks for "more negative," they're not adding a light — they're taking one away, in effect.

13. Silk / grid cloth Large frames of diffusion fabric used to soften sunlight or big sources over a wide area. A silk above a car creates even, overcast-sky quality light. Rigging large silks takes time and sometimes requires a scaffold or condor — factor this into your schedule.

Set language

14. Key light The primary, dominant light source on a subject. Everything else is built around it. Changing the key light mid-scene is a significant decision that affects continuity.

15. Fill light A secondary source that lifts the shadow side of the subject, reducing contrast. The ratio between key and fill determines how dramatic or flat the image looks. Fill decisions are often where the DP's visual style becomes most apparent.

16. Backlight / rim light Light directed at the back or edge of a subject, separating them from the background. Without it, subjects can visually merge into the set. On darker-skinned subjects or dark-costumed actors it's particularly important and takes careful placement.

17. Colour temperature (Kelvin) A measure of how warm or cool a light source appears, expressed in Kelvin (K). Daylight is roughly 5,600 K; tungsten is around 3,200 K. Mixing colour temperatures without intention reads as an error on camera. Matching or deliberately contrasting sources is a core part of the gaffer's job.

18. Dimmer / dimming Reducing a light's output electronically. Not all fixtures dim cleanly — some flicker at low levels, which is a problem at certain camera frame rates. This is worth a conversation before any high-speed or slow-motion work is locked in.

On the day

19. Electrical package The full suite of lighting equipment hired for the production: fixtures, stands, frames, cable, distro, and associated gear. The package is spec'd during prep based on the shot list and locations. Changes after the package is confirmed may affect cost and availability.

20. Wrap (electrical) When the lighting team begins packing down and loading out. Electrical wrap has to be done safely and methodically — cable coiled correctly, fixtures secured, distro de-energised in the right order. Rushing wrap causes damage and safety incidents. Build realistic wrap time into your schedule; it's rarely less than an hour on a full commercial day.

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The practical takeaway: most lighting conversations on set are about trade-offs — output versus softness, speed versus precision, budget versus ambition. The more clearly you can describe what you need and flag what's changing, the better those trade-offs get resolved before they affect your day.