Illuminance Converter
Convert between lux, kilolux, foot-candle, and phot, plus lumens for a room area.
Direct midday sun measures about 100,000 lux, an office desk 300-500.
Type in any field and the others update instantly. Add a room area and the lumens needed to reach that light level are worked out too.
Illuminance measures how much light lands on a surface, spread over its area. The SI unit is the lux (lx), defined as one lumen per square meter. It answers a practical question: is this surface bright enough to read, work, or photograph?
Key conversions:
- 1 klx = 1,000 lx (kilolux)
- 1 foot-candle = 10.764 lx
- 1 phot = 10,000 lx
The foot-candle (one lumen per square foot) is still standard in US lighting codes and stage lighting, so converting it to lux is the most common reason people end up here. The 10.764 factor is just the number of square feet in a square meter.
Light levels you can picture:
- Full moon on a clear night: about 0.25 lx
- A well-lit office desk: 300-500 lx
- An overcast day outdoors: around 1,000 lx
- Direct midday sun: 32,000-100,000 lx
That last jump surprises people. Even a bright office is more than a hundred times dimmer than stepping outside, which is part of why indoor plants sulk and why phone cameras behave so differently indoors and out.
Don’t confuse illuminance with lumens. Lumens (luminous flux) measure the total light a bulb throws in every direction; lux measures how much of that light reaches a given surface. A powerful bulb hung too high can still leave a desk underlit.
That relationship is what the area box above is for. Multiply the lux you want by the square metres you are lighting and you get the lumens the room needs, which is the number printed on every bulb box. A 12 m² kitchen at 300 lx wants about 3,600 lumens, and that is before you lose anything to shades, dark walls, or a fitting that throws half its output at the ceiling. Real installations usually need a third more than the bare arithmetic suggests.
Recommended light levels for common tasks (from the EN 12464-1 workplace standard, which most national codes follow closely):
| Space or task | Maintained illuminance |
|---|---|
| Corridors, stairs, circulation | 100 lx |
| Storage rooms, plant rooms | 150 lx |
| General office, classroom, reading | 300 lx |
| Detailed office work, drawing boards | 500 lx |
| Fine assembly, sewing, colour inspection | 750 lx |
| Precision electronics, jewellery, watchmaking | 1,000 lx |
Photographers meet the same quantity under a different name. An incident meter set to ISO 100 reads roughly EV = log2(lux ÷ 2.5), which puts full sun near EV 15, the exposure the old “sunny 16” rule was built around. It is the same physical measurement the lighting designer is making, only the camera world prefers to talk in stops.
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This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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