Every lighting datasheet quotes at least one of these three numbers, and almost every buying mistake in stage lighting comes from treating them as interchangeable.
Lumens, lux and candela measure three genuinely different things. A fixture can have high lumens and look dim on stage. A fixture can have modest lumens and be uncomfortably bright at twenty metres. Once you know which number answers which question, a datasheet stops being a marketing document and starts being a specification.
In this guide
A lumen (lm) measures luminous flux — the total quantity of visible light a source emits per second, weighted by how sensitive the human eye is to each wavelength. It is a property of the source and it has nothing to do with direction.
A bare lamp radiating in every direction and a well-engineered fixture with the same lamp inside can quote the same lumen figure while behaving nothing alike. The lumen number does not know that one of them has an optic in front of it concentrating the output into a 10° cone and the other is spilling light onto the ceiling. Both facts are true, and the lumen figure is identical.
This is the root of the most common purchasing error. Lumen is the only number on the box, so it becomes the number people compare — and it is the number that correlates least with how bright a fixture looks where you actually put the light.
On a moving head or a wash fixture, a quoted lumen figure is normally the unobstructed source output — measured at the emitter, before the optics, the gobo wheel, the colour wheel, the frost and the zoom lens get their turn. Every element in the optical path costs some light. How much varies enormously by fixture, by zoom position and by what is in the beam at the time. Treat a lumen figure as an upper bound, never as a delivered value.
A candela (cd) measures luminous intensity: how much light a source emits into one particular direction, per unit of solid angle. It takes the lumen figure and asks the question the lumen figure refuses to answer — where is it all going?
The relationship is straightforward. One candela is one lumen per steradian, where a steradian is a unit of solid angle and a full sphere is 4π of them, about 12.57. A source emitting 1,000 lumens perfectly evenly in every direction produces about 80 candela in any given direction. The same 1,000 lumens focused into a narrow cone produces far more candela, because the same total output is packed into a smaller angle.
That is the whole reason a 90 W pencil beam and a 200 W wash can feel comparable on a smoke-filled stage despite the wash having far more total output. The beam fixture is not brighter — it is concentrated. Concentration is what the eye reads as punch, and candela is the number that measures it.
| Unit | Measures | Depends on direction? | Typical use on a datasheet |
|---|---|---|---|
| Lumen (lm) | Total visible light emitted | No | Headline output figure; useful for comparing efficiency |
| Candela (cd) | Intensity in one direction | Yes | Throw capability and punch; the number that predicts reach |
| Lux (lx) | Illuminance at a surface | Yes | Illuminance tables and beam angle charts |
| Lumen per watt | Efficiency | No | Energy comparison between fixtures |
A lux (lx) measures illuminance: luminous flux arriving at one square metre of surface. It is the only one of the three units that describes the thing you actually care about — how much light is on the performer.
Lux is specifiable, measurable and targetable. You can name a target figure for a venue type, measure it with a meter, and adjust until you hit it. Lumen and candela are properties of hardware; lux is a property of the result.
| Illuminance | Where you meet it |
|---|---|
| 1 lx | Full moon on a clear night |
| 50 lx | Domestic corridor lighting |
| 150 lx | General room lighting, easy reading |
| 500 lx | Office and classroom standard |
| 1,000–1,500 lx | Typical stage wash for live performance |
| 2,000–3,000 lx | Key light on a face for camera work |
| 10,000 lx | Overcast daylight outdoors |
| 100,000 lx | Direct midday sun |
Two of those rows explain why outdoor daytime work is so difficult. If the sun delivers roughly 100,000 lux and your stage wash targets 1,500, you are asking a rig to compete with sixty-six times its own output. That is not a brightness problem you solve by buying brighter fixtures — it is a problem you solve by changing the schedule, adding shade, or accepting that the lighting will only read after dark.
The three units interconvert through two relationships, and both are simple enough to do on a phone. Having them in your head removes the need to trust a datasheet.
Because the same total output is being spread across four times the area. Distance doubles the radius, area goes with radius squared, so illuminance falls to a quarter. This is the single most consequential geometric fact in lighting design, and it is why front truss height matters more than fixture choice on a deep stage.
Two fixtures with identical lumen output and different beam angles will light a stage in completely different ways, and no datasheet that lists only lumens can express the difference.
Beam angle determines the area the fixture covers at a given distance, and therefore the lux that area receives. A narrow beam covers a small area at high intensity; a wide beam covers a large area at low intensity. The lumen figure is the same in both cases, which is exactly why it cannot be compared across fixtures with different optics.
The practical reading is that beam angle is a coverage decision, not a brightness decision. Choose the angle by asking what area one fixture should cover from where it will hang, then let the resulting lux figure tell you how many fixtures you need. Doing it the other way — buying on output and hoping the coverage works out — is how stages end up with hot centres and dark edges.
JUBARIS BEAM L90
$215
SPOTTY LED 90
$229
SPOTTY LED 150
$519
The method below takes about five minutes and removes most of the guesswork from a purchase or a rig plan. It works from published figures and needs no equipment.
One fixture in a 15° beam delivering roughly 6,500 cd at 6 m gives 6500 ÷ 36 = 181 lx at the centre of its pool. Five fixtures arranged across the width give about 900 lx through the covered area, and the overlap between adjacent pools lifts the working average toward the 1,000 lx band. Six fixtures with a little margin is the safe specification for a stage this size.
Datasheets are written to be quoted, not to be compared. A short checklist makes them useful again.
| What to look for | Why it matters |
|---|---|
| Lumen, candela or lux — which is given? | If only lumens, you cannot predict coverage. Look for an illuminance figure or an illuminance chart with distance. |
| Beam angle, and whether it is beam or field | Beam angle is the half-intensity point; field angle is where output effectively ends. Quoting field angle as “beam” inflates the coverage figure. |
| Measurement distance | Illuminance falls with distance squared. A figure quoted at 1 m is not comparable with one quoted at 5 m without arithmetic. |
| Conditions of measurement | Whether colour was in the beam, whether zoom was at wide or narrow, whether the gobo wheel was clear. Any of these can cost a large share of output. |
| Efficiency, if offered | Lumens per watt is comparable across fixture types and usefully reveals how much electrical power becomes heat rather than light. |
| Whether the number is calculated or measured | A manufacturer measuring on a calibrated bench and one quoting a calculated source figure produce very different numbers for similar products. |
When two fixtures cannot be compared on paper, compare them the same way the audience will. Hang both at the same height, aim both at the same wall from the same distance, set both to the same colour temperature, and photograph the boundary between their pools with a phone. It takes ten minutes and settles questions that no datasheet can. This is also the only reliable way to compare tint, beam quality and edge softness — none of which appear on any specification sheet at all.
Lumens measure the total light a fixture emits, in every direction it emits it, and say nothing about where the light goes. Lux measures how much light arrives at one square metre of a surface. A fixture can emit thousands of lumens and deliver very few lux if its output is spread widely or aimed somewhere else. Lux is the number that describes the result you can see; lumens describes the hardware.
No — and this is the most expensive assumption in stage lighting. A 90 W fixture with a 1.5° beam can put more light on a distant point than a much higher-lumen wash fixture, because it concentrates its output instead of spreading it. If brightness at a distance is what you need, compare candela or illuminance, not lumens.
You need two intermediate steps, because lumens to lux is not a direct conversion. First convert lumens to candela using the beam angle — a narrower beam produces far more candela from the same lumens. Then divide candela by the square of the distance in metres to get lux. If a datasheet gives illuminance at a stated distance, read that directly and skip the maths entirely.
Candela describes the intensity leaving the fixture in a particular direction. Lux describes the intensity arriving at a surface after travelling some distance. They are linked by the inverse square law: lux equals candela divided by distance squared. Candela is a property of the fixture and the optic; lux is a property of the geometry of your particular rig.
Because the lumen figure usually describes the source before the optics. Every element in the light path — the colour wheel, gobo wheel, frost, zoom lens, and even a saturated colour mix — removes some light. The losses accumulate, and they are largest at extreme zoom positions and with deep saturated colours. Treat the published figure as a ceiling.
A working range is 1,000–1,500 lux for a wash that reads clearly on performers, with more for front light on faces and less where you deliberately want atmosphere. Where the performance is filmed, 2,000–3,000 lux on faces is a more realistic starting point, because cameras have less latitude than the eye. Measure on a real rig once and your estimate becomes reliable for every future job.
Almost always beam angle. The same total output packed into a 10° cone produces far higher intensity than the same output spread across 45°, and the eye reads intensity as punch. Add differences in colour temperature, tint and optical quality and two fixtures with identical headline numbers can look like entirely different products.
It does not change the lumens — the same quantity of light leaves the fixture either way. It changes the area that light is spread across, which changes the illuminance at any given distance. Narrowing the beam concentrates the same output, raising the lux in a smaller area; widening it spreads the same output, lowering the lux across a larger area.
This article explains the standard photometric quantities lumen, candela and lux, and describes general measurement and planning practice. Published figures for products sold on sanyilights.us are quoted from the current datasheet at the time of writing and vary with operating mode, colour mix, zoom position and firmware version. Photometric values are inherently conditional: always confirm the measurement distance and beam condition before comparing products, and verify on a real rig with a meter where the result matters. Product availability and pricing are subject to change.
