Illuminance is how much light falls on a surface — luminous flux per unit area. The SI unit is the lux (one lumen per square metre); the US customary unit is the foot-candle. This converter moves between lux, kilolux, foot-candle, phot, lumen/m² and nox using exact factors.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: SI photometric definitions, recomputed in code.
How conversion works
Each unit has a fixed factor to lux: kilolux 1000, foot-candle 10.76391, phot 10000, lumen/m² exactly 1, and nox 0.001. To convert, the value is first expressed in lux, then divided by the target unit's factor. The foot-candle factor is the number of square feet in a square metre, because a foot-candle is a lumen per square foot while a lux is a lumen per square metre.
Worked examples
1000 lux to foot-candles:
50 foot-candles to lux:
1 phot to lux:
For context, an office lit to 500 lux is about 46 foot-candles, bright daylight shade near 20,000 lux is roughly 1,858 foot-candles, and a phot — 10,000 lux — sits between an overcast and a clear day outdoors.
Frequently Asked Questions
SI: lux (1 lumen/m²). US: foot-candle (1 lumen/ft²). Phot and nox are older units.
Divide by 10.76391. 1000 lux ≈ 92.9 fc. Multiply to go back.
10.76391 lux — the square feet in a square metre.
One lumen per cm² = 10,000 lux. A legacy CGS unit.
About 300–500 lux. Sunlight ≈ 100,000 lux; full moon ≈ 1 lux.