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Stage Lighting Power Requirements: Calculate Your Needs
Practical steps for calculating stage lighting power draw per circuit, per phase, and over long cable runs.
A stage lighting power calculation is not a job for the venue electrician at the end of a long day, and it is not a number you can estimate from the fixture count. For a rental company or a performance venue, power planning decides which distros you pack, which cable runs you pull, and whether the show trips before the first cue. Get the basics right, and every rig is safer and cheaper to run.
This guide goes through the practical side: reading fixture nameplates, working with power factor, leaving headroom on breakers, balancing three-phase distros, and checking voltage drop over long runs. The examples use common fixture types, but the method applies to any brand, including the moving heads, pars, and strobes in the YC Light product range.
Read the Nameplate, Not Just the Lamp Wattage
A common mistake is to take the lamp wattage printed in the fixture marketing and treat it as the total load. A 230W beam moving head can draw 350W to 450W in practice once you add the ballast, power supply, cooling fans, and pan/tilt motors. An LED moving head may have a 300W LED engine and still consume noticeably more at the plug. The number that matters for your breakers and cables is the input current printed on the fixture, usually given in amps at a specific voltage, for example 1.6A at 230V.
The nameplate is only valid at the stated voltage. The same fixture at 208V draws more current than at 240V for the same power setting. If your inventory tours between regions, check the voltage range on the label and run the calculation at the lowest voltage the venue can supply.
A Straightforward Stage Lighting Power Calculation
The core stage lighting power calculation for a single fixture is simple: current in amps equals power in watts divided by the product of voltage and power factor.
For a resistive load like a tungsten par or a fogger heater, the power factor is close to 1, so watts divided by voltage gives the right current. LED fixtures and other switch-mode devices sit below unity, typically in the range of 0.90 to 0.98. Use the power factor from the fixture datasheet. If the datasheet only gives watts, assume a slightly higher current rather than a lower one.
Worked example: a 400W LED moving head at 230V with a power factor of 0.95 draws about 1.8A. Twelve of them draw in the region of 22A, which is more than one common circuit should carry for a full show, so you split them across two or three circuits.
Never total the watts, divide by the mains voltage, and call it the current. On a three-phase distro you must sum the amps per phase. Twelve fixtures arranged as four per phase is a different picture from twelve fixtures all landed on the same phase.
Circuit Loading, Breakers, and Phase Balancing
Stage lighting is a continuous load. A show runs for hours, so breakers should be loaded below their marked rating rather than right up to it. A 16A breaker gets a comfortable margin, and a 20A breaker gets the same treatment. This is not an over-cautious habit; it protects the breaker from heat build-up and leaves room for the brief current surges that fixtures produce during movement or lamp ignition.
The table below shows typical figures for common fixture types. These are representative values for planning, not a substitute for the datasheet of the exact fixture in your inventory.
| Fixture type | Typical running draw | What to watch |
|---|---|---|
| LED par, 18 x 15W | 100–150W | Low current per unit, so it is easy to overload a circuit by unit count alone |
| LED moving head wash | 280–400W | Power factor below 1; fans and motors add current peaks |
| Beam moving head, 230W discharge | 350–450W | Lamp ignition inrush; avoid hot restrike |
| LED strobe | 200–600W | Short high-current bursts when all LEDs fire |
| Hazer or fogger | 500–1500W | Heater cycles cause the load to swing |
Balance the load across phases. If your distro provides three phases, distribute fixtures so each phase carries roughly the same current. An unbalanced rig wastes capacity and raises the current on the neutral conductor. This last point matters even more with LED fixtures, because their switch-mode power supplies add harmonic currents that accumulate on the neutral. Keep the neutral conductor sized for the worst case, not for a perfectly balanced rig.
Voltage Drop and Long Cable Runs
Every cable run has resistance, and that resistance drops voltage before the fixture sees it. The drop is small on a 10m feeder and meaningful on a 60m run to a truss or a followspot tower. LED drivers can shut down or flicker when the input voltage falls below their operating range, so voltage drop is a reliability issue, not just a cable-sizing issue.
As a working rule, keep the voltage drop at the last fixture under a few percent. If you are close to the limit, step up one conductor size instead of extending the run. The same current loses twice as much voltage on a 120V system as on a 240V system, which is why touring production prefers 240V or 400V three-phase distribution wherever possible.
Measure the result. Before the show, check the voltage at the distro and at the last fixture while the rig is at full load. The difference between the two readings is the real voltage drop on that feeder.
A Stage Lighting Power Calculation Worksheet
Build the calculation in the same order for every show so nothing is missed. This checklist works for touring rigs and permanent installs.
- Record the input current for every fixture model at the actual venue voltage, not the nominal voltage on the label.
- Count the fixtures per circuit, per dimmer channel, and per phase.
- Apply a continuous-load margin so no breaker runs hot through an entire show.
- Balance the current across the three phases of the distro.
- Add non-lighting loads on the same distro: hazers, followspots, practicals, and monitor systems.
- Check the feeder length for each run and allow for voltage drop.
- Compare the total calculated current with the mains or generator capacity.
- Label every distro and feeder with its rated current and its connected load.
Once these numbers are in place, the rest of the plan, cable sizes, breaker ratings, and generator sizing, follows from the same figures.
Special Cases: Inrush, Heaters, and Generators
Discharge lamp fixtures draw a heavy current for a few seconds when the lamp ignites, especially from a cold start. Breakers usually tolerate this brief surge, but a dimmer pack or relay already running near its limit may not. Stagger the power-on sequence so fixtures come up in groups rather than all at once. This matters if your rig is heavy on beam moving heads, which combine lamp ignition with motor start-up.
LED fixtures have start-up inrush as the internal capacitors charge, and motorized heads draw extra current while pan and tilt move fast. Both are normal, and both explain why a rig that sits at 15A when idle can trip a 16A breaker during a fast chase. Leave movement headroom.
Foggers and hazers are resistive heater loads. A 1500W hazer draws more than 6A at 230V whenever the heating element is on, and it cycles on and off, so the load at the distro never stays still. Give heaters their own circuits and keep them away from LED drivers that are sensitive to voltage dips.
Generators add another layer of caution. A generator sized for total running amps can still struggle with the non-sinusoidal current drawn by switch-mode supplies. If the generator is working hard, reduce the connected load rather than relying on a higher throttle setting.
Frequently Asked Questions
Why does the measured current go up when the venue voltage is lower?
Because most fixtures consume roughly constant power. A 400W fixture draws more amps at 208V than at 240V. Always calculate at the lowest voltage the venue can actually deliver, not the nominal voltage printed on the fixture.
Should I use watts, volt-amperes, or amps?
Use the input current in amps whenever the datasheet provides it. If only watts and VA are given, use the VA figure, because it includes power factor and represents the true load on the cable and the breaker.
Can I load one circuit with many small LED pars?
Only up to the circuit limit. A small LED par draws only a few hundred milliamps, but multiply that by 30 fixtures and add the power supply losses, and the total is real. Count units, multiply, then apply the continuous load margin, and the answer will be close to what a clamp meter shows at the distro.
Do dimmer settings change the load calculation?
For resistive loads, the current changes with the dimmer level, so the worst case is full output. For LED fixtures on dimmers, the driver, control electronics, and fans keep drawing current even when the light output is low, so load the circuit by the fixture maximum input, not by the dimmer level.
Once your stage lighting power calculation is solid, choosing fixtures and distros becomes straightforward. If you want to check the numbers against real fixture datasheets, or you need help planning power for a specific project, the YC Light team can work through the fixture list with you. Get in touch with your rig layout and we will help you match the fixtures to your power plan.