Stage Lighting Power Calculator: Dimmer Channels, Circuits, Amps per Phase, Generator & DMX
Add up a lighting rig: watts and amps for tungsten, LED and moving-head fixtures at 120 V or 230 V, fixtures per dimmer channel, non-dim circuits packed fixture by fixture with the 80% rule, amps on each phase of a three-phase feed, feeder and generator size, DMX channels, universes and lines, cable size and heat load.
How it works
current (A) = W ÷ V for tungsten; W ÷ (V × PF) for LED and moving heads · fixtures per dimmer channel = ⌊channel W × max load ÷ fixture W⌋ · fixtures per circuit = ⌊breaker A × 80% ÷ fixture A⌋ · three-phase: circuits spread over L1/L2/L3, feeder ≥ heaviest phase ÷ 0.8 · generator kVA ≥ kW ÷ 0.8 PF ÷ 0.8 loading · DMX universes: 512 channels each, 32 devices per line · heat: 1 W = 3.412 BTU/h, 12,000 BTU/h = 1 ton
A lighting rig's power plan comes straight from the fixture list. Tungsten lamps are resistive, so they draw their rated watts divided by the voltage, and they run through dimmer channels of fixed capacity; the calculator puts whole fixtures on each channel up to the load limit you choose. LED fixtures and moving heads take roughly constant power through non-dim circuits, and because their power supplies have a power factor below 1 they draw a little more current than watts ÷ volts. Lighting counts as a continuous load, so circuits are filled to 80% of the breaker, fixture by fixture, since a fixture cannot be split between two circuits. On a three-phase feed (208Y/120 V in North America, 400Y/230 V elsewhere) the circuits are spread across the three phases, largest first, and the heaviest phase sets the feeder size. Generators are rated in kVA at a 0.8 power factor and should run at no more than about 80% of their rating, which is where the generator figure comes from. Every watt of light and electronics ends up as heat in the room. The DMX count uses one address per dimmer channel plus each fixture's mode, keeps fixtures whole within a universe, and checks the 32-device limit of a DMX line.
Worked example
Twenty-four 575 W profiles, sixteen 150 W LED washes and eight 350 W moving heads add up to 19.0 kW. At 120 V the tungsten draws 13,800 ÷ 120 = 115 A and the LED and movers 5,200 ÷ (120 × 0.95) = 45.6 A, 161 A in total. A 2.4 kW dimmer at 90% carries 2,160 W, so 3 profiles each: 8 channels, or 2 six-channel packs. A 20 A circuit at 80% gives 16 A, enough for 12 LED washes (1.32 A each) or 5 moving heads (3.07 A each), so the LED needs 2 circuits and the movers 2. Spread as whole circuits over 208Y/120 V three-phase, the heaviest phase carries 57.5 A (four dimmer channels), and 57.5 ÷ 0.8 = 71.9 A needs a 100 A per phase feeder; a generator needs 19.0 ÷ 0.8 ÷ 0.8 = 29.7 kVA, so a 30 kVA unit. DMX uses 8 + 128 + 160 = 296 channels in one universe and 26 devices on one line, and the rig puts about 64,828 BTU/h (5.4 tons) of heat into the room.
Sources: Set Power Calculator: 80% rule, fixtures that cannot be split across circuits (FilmAndVideoLighting) · Power load calculations: 80% continuous loading, phase balance, generator loading (MDP SOPs) · How many fixtures on one DMX line: 32 unit loads, 512 channels, 120 Ω termination (ENTTEC) · Lighting circuit wattage load calculator: continuous-load planning and dimmer derating (DIY Smart Home Hub)
Frequently asked questions
How many lights can I put on a 20 amp circuit?
At 120 V a 20 A circuit gives 2,400 W, but lighting is a continuous load, so plan for 80%: 16 A or 1,920 W. That is three 575 W profiles, twelve 150 W LED washes or five 350 W moving heads. At 230 V a 16 A circuit at 80% gives about 2,940 W.
Can LED fixtures go on dimmer circuits?
Only on channels set to non-dim, switched or relay mode. A phase-cut dimmer output, even parked at full, produces a chopped waveform that can damage LED power supplies and cause flicker. Use constant-power outputs or ordinary circuits.
How do I size a generator for a lighting rig?
Add up the watts, divide by 0.8 because generators are rated in kVA at a 0.8 power factor, and divide by 0.8 again so the set runs at no more than about 80% of its rating. A 19 kW rig needs about 30 kVA. Balance the load across the three phases and allow for the inrush of LED power supplies.
How many DMX universes do I need?
Add the channels of every fixture in the mode you will use, plus one address per dimmer channel. Each universe holds 512 channels, and a fixture cannot be split between universes. Separately, one DMX line carries at most 32 devices (unit loads); beyond that, use a splitter.
Why does the current on each phase matter?
On a three-phase feed each phase has its own breaker or fuse, so the feeder is sized by the heaviest phase, not the average. Spreading circuits evenly also keeps the neutral current low, which matters with the harmonic currents of LED power supplies.
How much heat does stage lighting produce?
Essentially all the electrical power becomes heat: 1 W is 3.412 BTU/h. A 19 kW rig adds about 65,000 BTU/h, or 5.4 tons of air conditioning, which is why tungsten-heavy rigs make small venues hot.
Related calculators
Planning figures for stage and event lighting power. Electrical installations, tie-ins and generator connections must follow local codes (NEC Article 520/525, BS 7909, IEC 60364 or your local equivalent) and be made by qualified people; never exceed dimmer, breaker, cable, connector or generator ratings.