Illuminance Converter
Convert between lux, kilolux, foot-candle, and phot illuminance units.
Enter any value to update all others — direct sunlight measures about 100,000 lux.
Type in any field — the others update instantly.
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.
How we build and check this converter
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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