Watt is the one number on a lighting datasheet that everybody already understands, and it is the wrong number for almost every question you actually have.
A watt tells you what the fixture costs the electrical supply. It does not tell you how much light leaves the lens, how far that light reaches, or how many of them fit on one circuit. For most of stage lighting history the shortcut worked anyway, because every fixture turned electricity into light at roughly the same rate. That stopped being true when LEDs arrived, and the habit of comparing watts survived it.
In this guide
A watt is one joule of energy per second. It measures the rate at which electrical energy is delivered to a device, and that is all it measures. It is an input figure, taken at the wall, before the driver, before the emitter, before the optics.
How much of that energy leaves as visible light is a completely separate question, decided by the technology inside. A 200 W fixture built on an incandescent filament and a 200 W fixture built on white LEDs draw identical power and produce wildly different amounts of light. The wattage is the same. Nothing else is.
The confusion is understandable, because for decades the shortcut was nearly honest. Tungsten halogen converts electricity to light at roughly 15–25 lumens per watt across every manufacturer, every model and every price point. The band is narrow. When every fixture in the catalogue converts energy at about the same rate, the wattage column becomes a usable proxy for brightness — and an entire vocabulary grew around it. “A 575” was not just a power figure; it was a recognised size of light with known brightness, known heat and known cable requirements.
Power draw. A 1,000 W fixture draws about 8.33 A at 120 V and about 4.35 A at 230 V, and that number is almost exactly true regardless of what technology is inside, because the electricity meter does not care how good the emitter is. Wattage is a reliable input for circuit planning, generator sizing and cable selection — and an unreliable input for anything to do with how bright the fixture looks.
The number that turns a watt into a brightness comparison is luminous efficacy: total light output divided by electrical power, expressed in lumens per watt (lm/W). It is the exchange rate between electricity and light, and it varies by more than a factor of ten between fixture classes.
Efficacy also has a theoretical ceiling. If a light source were perfectly efficient at the wavelength the human eye is most sensitive to — 555 nanometres, a yellow-green — it would produce 683 lumens for every watt it consumed. No real source reaches that, and a source that emits across the whole visible spectrum rather than at one wavelength mathematically cannot. But the ceiling is what makes efficacy meaningful: it is a direct statement of how much of the electricity is doing visible work.
The last two rows of that chart are the ones to sit with. A bare white LED emitter can be measured at well over 100 lm/W, and it is tempting to treat that as the fixture’s efficiency. It is not. A stage fixture puts a colour wheel, a gobo wheel, a frost flag, an iris and a zoom lens between the emitter and the audience, and each element removes light. By the time the beam leaves the lens, a fixture built on 130 lm/W emitters commonly measures 30–60 lm/W as a whole unit — which is still roughly triple what tungsten managed, but nothing like the emitter figure.
A “140 lm/W” claim on a datasheet is very likely a measurement of the LED chip, taken on a bench with no optics in the path. A “45 lm/W” figure for a finished stage fixture includes everything the light has to pass through. Both numbers are honest; comparing them is not. When two datasheets quote lm/W, check what was measured before you draw a conclusion.
Old wattage ratings carried four different pieces of information at once, and that is precisely why they were so sticky. A tungsten fixture’s rating told you how bright it was, how much heat it produced, how many amps it needed, and how many would fit on a circuit. Nothing else needed to be looked up.
LED broke the bundle. Two fixtures with the same wattage now differ in brightness by a factor of three or more, so the four pieces of information have to be found separately. The wattage still answers the circuit question. It no longer answers any of the others.
| What the old rating told you | What you have to look up now |
|---|---|
| Brightness | Lumen output, and then candela or illuminance if you need to know how far it reaches |
| Heat produced | The rest of the wattage after the light is subtracted — which means you need the efficacy first |
| Current draw | Still simply the wattage. This is the one question the old habit still answers correctly |
| Fixtures per circuit | Wattage, but re-checked against the fixture’s actual power factor and inrush behaviour |
The practical consequence is a specific and expensive mistake: buying an LED fixture whose wattage matches the tungsten fixture it replaces and expecting a similar result. A 575 W tungsten fixture delivers roughly 10,000 lumens. An LED fixture rated at 575 W, at a whole-unit efficacy of about 45 lm/W, delivers something in the region of 26,000 lumens — two and a half times the light from the same wattage. The matching-wattage purchase is not wrong so much as enormously over-specified, and the budget that went into it was spent on something the stage never needed.
Everything that does not leave as visible light leaves as heat. This is not a side effect to be managed at the end of the design; it is the direct arithmetic consequence of the efficacy figure, and it is the reason a tungsten rig and an LED rig feel like different working environments even when they produce comparable light.
At 17.4 lm/W, a 575 W tungsten halogen fixture converts roughly 3% of its input into visible light and the remaining 97% into heat — some radiated as infrared, most carried away by convection. That is a 575 W heater that happens to glow. At 45 lm/W, an LED stage fixture converts roughly 7% into light and 93% into heat. Better than double the light per watt, and still over ninety percent heat.
Heat has practical costs that show up long before anyone measures them. Coloured gel in front of a hot fixture saturates and shifts within a show or two. Truss-mounted fixtures warm the air directly above the stage, which is exactly where performers stand. Rooms with fixed air conditioning load up faster, and fixtures inside enclosed positions derate themselves or shut down when their own thermal limits arrive. Choosing a lower-wattage fixture of equal light output removes all of these pressures at once — not because the fixture is cleverer, but because there is less waste heat to move.
This is the domain where the wattage figure remains the correct and only useful number. Current draw follows directly from power and supply voltage: I = P ÷ V. A 200 W fixture draws about 1.67 A at 120 V; a 1,000 W fixture draws about 8.33 A. Change the supply to 230 V and both roughly halve, which is why the same rig looks very different to a North American and a European electrician.
The other half of the calculation is the derating rule. A 20 A breaker should not be loaded to 20 A continuously. For anything running for more than a few minutes, keep the load to about 80% of the rating — roughly 1,920 W on a 20 A / 120 V circuit — so that the breaker does not nuisance-trip once the room warms up and the fixtures have been on for an hour.
| Fixture power | Current at 120 V | On one 20 A circuit (80% derate) |
|---|---|---|
| 200 W | 1.67 A | 9 fixtures |
| 300 W | 2.50 A | 6 fixtures |
| 480 W | 4.00 A | 4 fixtures |
| 600 W | 5.00 A | 3 fixtures |
| 1,000 W | 8.33 A | 1 fixture |
Stack that up against a real rig and the difference becomes structural rather than incremental. Twelve fixtures delivering roughly 10,000 lumens each is 12 × 575 W = 6.9 kW on tungsten, drawing about 58 A and needing four 20 A circuits. The same delivered light from 12 × 222 W LED fixtures is 2.67 kW, about 22 A, and two circuits. Fewer cables, a smaller distro, less weight on the truss, and two spare ways on the rack.
DT 200W COB
$169
PULSARIS 3000IP
$899
Once wattage stops being a shortcut, a short method replaces it. Four numbers, in this order, will answer almost every comparison question correctly.
There is one comparison where watts can be actively misleading in the other direction. A narrow beam fixture can put more usable light on a distant point than a fixture with several times its output, because it concentrates what it has into a small solid angle. Judging it by wattage gets the answer exactly backwards.
JUBARIS BEAM L90
$215
VERSATILIS 300BSW
$1,999
The clearest way to see the whole subject is to fix the output and compare what it costs to produce. Suppose you want 10,000 lumens from one position — a reasonable target for a front light covering a stage section.
Tungsten draws 34.50 kWh per night, about $8.62. LED draws 13.33 kWh, about $3.33. Over fifty nights the difference is roughly $265 on electricity alone, before a single lamp change, cable, distro rental or air-conditioning hour is counted. The fixtures cost more up front — that is a real trade, not a free one — but the running side accumulates quietly and without intervention.
Two honest exceptions. First, if you need a specific quality of light that only one technology produces, efficacy is irrelevant — pick for the look. Second, if you already own the fixture, the electricity you would save by replacing it may never repay the purchase; the switch makes sense on new purchases and on rigs where the circuit, weight or heat load is the binding constraint. Efficiency is a strong argument, not an unconditional one.
Not on its own, and not reliably. Wattage measures electrical input; brightness depends on how efficiently that input becomes visible light. Two fixtures of the same wattage can differ in output by a factor of three or more depending on the technology and the optics. Compare lumen output, or better still illuminance at the distance you will actually use them. Watts tell you how much power they use, which is a different and much narrower fact.
It is luminous efficacy — light output divided by power input. It converts a power figure into a brightness figure, and it is the only fair way to compare fixtures built on different technologies. A tungsten halogen fixture manages around 20 lm/W; a finished LED stage fixture typically reaches 30 to 60 lm/W once the light has passed through its optics. The higher the number, the less of your electricity turns into heat.
Because it compares against a technology the fixture no longer uses. A 1,000 W rating meant something specific when every fixture converted electricity at the same rate; the same wattage in LED produces several times the light. The claim also hides which measurement was used — an emitter figure or a whole-fixture figure — and the two can differ by a factor of three. Ask for lumens, and for the distance at which illuminance was measured.
Keep the load to about 80% of the rating for continuous use, which is roughly 1,920 W on a 20 A / 120 V circuit. That works out to nine 200 W fixtures, six 300 W fixtures, three 600 W fixtures or a single 1,000 W fixture. Real fixtures draw a brief inrush on start-up, so do not spend the margin on paper — leave it in the rig.
Because even a good stage fixture converts only around 7% of its input into visible light. The remaining 93% still has to go somewhere, and it leaves as radiated infrared and as heat carried away by air. An LED fixture is roughly twice as efficient as tungsten, which is a large improvement and nowhere near a solution — every watt you draw has to leave the fixture in some form.
Yes, for everything on the electrical side. It predicts current draw, how many fixtures fit on a circuit, what cable gauge you need, whether a generator can carry the rig, and how much heat the room has to absorb. That is a genuinely valuable set of answers. The mistake is using it for the one question it cannot answer, which is how bright the fixture looks.
In this order: compare illuminance or candela at your working distance; compute lumens per watt for each; check the beam angles are comparable for the job; and only then check the wattage for circuit planning. If one datasheet gives only lumens and no beam angle, it does not contain enough information to plan with, regardless of how impressive the number looks.
For the same delivered light, yes, and the difference is easy to compute. Take the power draw of each option, multiply by hours per night, convert to kilowatt-hours, and multiply by your electricity rate. Twelve tungsten fixtures delivering 10,000 lumens each cost roughly $8.62 a night at $0.25 per kWh; the LED equivalent costs about $3.33. The fixtures cost more up front, so the question is how many nights you will run them.
This article explains the relationship between electrical power, luminous efficacy and light output, and describes general electrical planning practice. Efficacy bands quoted here are typical industry values for each source class, not specifications of any particular product — individual fixtures vary with power level, colour temperature, drive current and optical configuration. Current figures assume a resistive load at unity power factor; real fixtures include power-factor correction and start-up inrush and should be verified against their own nameplate ratings. Circuit capacity must always be confirmed by a qualified electrician against local code and the actual supply. Published figures for products sold on sanyilights.us are quoted from the current datasheet at the time of writing. Product availability and pricing are subject to change.
