Illumination Converter

Illuminance is how much light falls on a surface: the luminous flux, in lumens, landing on each unit of area. Its SI unit is the lux (lx), one lumen per square meter. In the US, lighting is often specified in foot-candles (fc), one lumen per square foot.

For a sense of scale: full moonlight is about 0.1–0.3 lux, a living room about 100–200, an office desk about 300–500, and full daylight 10,000–100,000.

How to convert lux and foot-candles

Type a value into any field, and every other unit is calculated at once. A square meter is 10.7639 square feet, so:

1. Foot-candles to lux: multiply by 10.7639.

   50 fc × 10.7639 = 538.2 lux

2. Lux to foot-candles: divide by 10.7639.

   500 lux / 10.7639 = 46.45 fc

Common conversions

Illuminance units

• Lux (lx): Lux is the unit of Illuminance in the International System of Units (SI), measuring lumens per square meter (lm/m²), or the illumination produced by luminous flux of one lumen falling perpendicularly on a surface of one square meter.
  Conversion Factor: 1 lx = 1 lm/m²

• Meter-candle (m•c): An older unit of illumination, equivalent to lumen per square meter.
  Conversion Factor: 1 m•c = 1 lm/m² = 1 lx

• Centimeter-candle (cm•c): Similar to meter-candle, centimeter-candle is an older unit of illuminance, equivalent to lumen per square centimeter.
  Conversion Factor: 1 cm•c = 1 lm/cm² = 10000 lx

• Foot-candle (f•c): Foot-candle is also an older non-SI unit, representing lumen per square foot.
  Conversion Factor: 1 f•c = 1 lm/ft² = 10.764 lx

• Flame (flame): Flame is an old unit of illuminance, equal to 4 lumens per square foot. Conversion Factor: 1 flame = 4 lm/ft² = 43.056 lx

• Phot (ph): Phot measures illuminance in terms of the luminous flux incident on a surface. One phot is equivalent to one centimeter-candle and is equal to 10 kilolux.
  Conversion Factor: 1 ph = 10000 lx

• Nox (nx): Nox is a unit of illuminance used to measure low illumination (dark night) and is equal to one millilux.
  Conversion Factor: 1 nx = 0.001 lx

• Lumen per square meter (lm/m²): The illumination produced by luminous flux of one lumen falling perpendicularly on a surface of one square meter.
  Conversion Factor: 1 lm/m² = 1 lx

• Lumen per square centimeter (lm/cm²): The illumination produced by luminous flux of one lumen falling perpendicularly on a surface of one square centimeter.
  Conversion Factor: 1 lm/cm² = 10000 lx

• Lumen per square foot (lm/ft²): The illumination produced by luminous flux of one lumen falling perpendicularly on a surface of one square foot, commonly used in the United States.
  Conversion Factor: 1 lm/ft² = 10.764 lx

• Watt per square centimeter (W/cm²): Watt per square centimeter measures the power per unit area, providing information on energy concentration. The conversion between illuminance (lux) and irradiance (W/cm²) depends on the spectral distribution of the light source. The conversion factor of 1 watt at a wavelength of 555 nm is equal to 683 lumen.
  Conversion Factor: 1 W/cm² (at 555nm) = 683 lm/cm²

Frequently asked questions

What is the difference between lux and lumens?

Lumens measure the total light a lamp gives out, and lux measure how much of it lands on each square meter. A 1,000-lumen bulb spread evenly over 10 m² lights it at 100 lux.

How many lux do I need?

Common recommendations are about 300–500 lux for office work and reading, 500–1,000 for detailed work, and 100–200 for living areas.