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The combined lumen output of all fixtures illuminating the room.
Add up the rated lumen output (from the bulb/fixture packaging or spec sheet) of every fixture illuminating the space.
The floor area being illuminated.
The area the target illuminance actually applies to, which is usually the task area rather than the whole room. Lighting a drawing office and its corridor to the same level is how a scheme ends up over-lit and over-budget; count them separately and light each to what it needs. Where the task plane is a bench rather than the floor, the area is the same but the mounting height above it is not, which is what the spacing then depends on.
Average illuminance
196 lux
This gives an average illuminance across the full area only — it does not account for light distribution pattern, mounting height, fixture spacing uniformity, or surface reflectance, all of which affect actual illuminance at any specific point. Use professional lighting design software for a point-by-point illuminance layout.
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Lighting Illuminance (Lux) Calculator: 196 lux — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Illuminance = total lumens ÷ illuminated area, the basic photometric relationship defining lux (lumens per square meter)
Inputs used
- Total Fixture Output (Lumens)
- 4000
- Illuminated Room Area
- 220 sq ft
Confidence note: This gives an average illuminance across the full area only — it does not account for light distribution pattern, mounting height, fixture spacing uniformity, or surface reflectance, all of which affect actual illuminance at any specific point. Use professional lighting design software for a point-by-point illuminance layout.
What this calculation does not cover
- The lumen figure you type is a rated, day-one output and nothing in the division shrinks it with age: lamp lumen depreciation, dust on lenses and dirt on room surfaces all pull the real level below this number long before the fixtures are replaced.
- Bulb lumens and luminaire lumens are treated as the same quantity here, since whatever total you add up is divided straight into the area, so light absorbed inside a shade, diffuser or recessed housing is counted as though it landed on the floor.
- Only fixture output is counted. There is no daylight, rooflight or borrowed-light term, so this is the artificial level with everything switched on after dark, not what a glazed room actually sees at midday.
- The total is taken with every fixture at full output, and dimming level, separately switched zones and occupancy or daylight controls have no term in the arithmetic, so a space lit by one of three switch groups will measure a fraction of the figure shown.
- Entries are capped at 50,000 lumens and 500 m² of floor, which rules out a warehouse bay or a sports hall in one pass; because the answer is a straight ratio, you can enter a representative portion of a larger space with its share of the fixtures and read the same lux.
- The answer arrives as a bare lux figure with no footcandle equivalent (a footcandle is 10.76 lux, being lumens per square foot rather than per square metre) and no comparison against a recommended level for the task, so a result of 200 carries no verdict on whether it suits the room.
Add the equipment this sizes
This result is a specification — 196 lux — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Part of bigger jobs
This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.
Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-05 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Illuminance = total lumens ÷ illuminated area, the basic photometric relationship defining lux (lumens per square meter)
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Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.