Illuminance Converter
Convert light levels between lux, foot-candles and phots.
How to use this calculator
- 1Enter the value you want to convert.
- 2Pick the unit you are converting from and the one you want.
- 3The table below shows the same value in every other supported unit.
How the calculation works
result = (value × factor(from) ) / factor(to)- factor
- How many lux one unit represents
Every value is converted to lux first, then out to the target unit. This means n units need n factors rather than n² conversion pairs.
Illuminance is luminous flux per unit area — lumens spread over a surface. Lux is lumens per square metre and foot-candles are lumens per square foot, so the conversion factor is exactly the square-foot-to-square-metre ratio, 1/0.3048² = 10.7639.
Illuminance is not the same as luminous flux. A lamp emits a fixed number of lumens; how many lux that produces depends entirely on how far away the surface is and how the light is distributed. Doubling the distance quarters the illuminance under the inverse-square law.
Worked example
50 foot-candle (lumen per ft²) to lux (lumen per m²)
- 1.One foot-candle (lumen per ft²) is 10.76391 lux, so 50 fc is 538.19552 lux.
- 2.One lux (lumen per m²) is 1 lux, so divide: 538.19552 ÷ 1 = 538.19552.
- 3.Put another way, 1 fc = 10.76391 lx.
Result: 538.19552 lx
What this assumes, and where it stops
Assumptions
- Conversion factors follow the internationally agreed definitions of each unit.
Limitations
- Converts illuminance only. Luminous flux (lumens), luminous intensity (candela) and luminance (cd/m²) are different photometric quantities that cannot be converted to lux without knowing the geometry.
Common questions
How many lux is a foot-candle?
Exactly 10.7639 lux, which is the number of square feet in a square metre. Both units measure lumens landing on a surface; they differ only in whether that surface is measured in feet or metres. Foot-candles remain common in North American lighting design, lux everywhere else.
Can I convert lumens to lux?
Not without knowing the area the light falls on. Lumens measure total light output from a source; lux measures how densely that light lands on a surface. A 1,000 lumen lamp produces 1,000 lux on one square metre, but only 250 lux if spread over four square metres — the same lamp, four times further away.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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