Illumination Converter
Convert illumination (illuminance) between lux, foot-candle, phot, nox, kilolux and more. Choose any source and target unit for an exact, instant answer.
Illumination Formula
Each illumination unit is a fixed multiple of the lux (lx), which is one lumen per square meter. Convert by multiplying the value by the factor of the source unit and dividing by the factor of the target unit. The foot-candle is one lumen per square foot, so its factor comes from the exact size of the foot (0.3048 m), giving 1 fc = 1 ÷ 0.09290304 lx. The tool uses the full-precision factor, not the rounded 10.764 or the rough 10 used for quick estimates.
What Is Illumination (Illuminance)?
Illumination, more precisely called illuminance, measures how much visible light falls on a surface. Its SI unit is the lux (lx), defined as one lumen spread evenly over one square meter. Moving a lamp farther from a desk spreads the same lumens over a bigger area, so the lux level on the desk drops.
Different regions use different units. The foot-candle (fc) is one lumen per square foot and is common in the United States. The phot (ph) is the CGS unit, one lumen per square centimeter, equal to 10,000 lux. The nox is a very small unit equal to 0.001 lux (one millilux), used for very dim light such as night-time scotopic vision. The kilolux (klx) is 1,000 lux and is handy for daylight.
Illuminance is not the same as brightness of a surface: that is luminance, covered by our Luminance Converter. For the strength of a light source in one direction, see the Luminous Intensity Converter.
Supported Illumination Units
Every unit below is converted through its exact definition in lux.
| Unit | Symbol | 1 unit equals (in lx) | Basis |
|---|---|---|---|
| Lux | lx | 1 lx | SI unit (1 lm/m²) |
| Kilolux | klx | 1,000 lx | Exact |
| Millilux | mlx | 0.001 lx | Exact |
| Foot-candle | fc | 10.7639104167 lx | Exact (1 ÷ 0.09290304) |
| Phot | ph | 10,000 lx | Exactly 1 lm/cm² |
| Milliphot | mph | 10 lx | Exact |
| Nox | nox | 0.001 lx | Exactly 1 millilux |
| Lumen per square meter | lm/m² | 1 lx | Exactly 1 lux |
| Lumen per square centimeter | lm/cm² | 10,000 lx | Exactly 1 phot |
| Lumen per square foot | lm/ft² | 10.7639104167 lx | Exactly 1 foot-candle |
How to Use the Illumination Converter
- Enter the illumination value. Decimals and scientific notation, such as 350 or 2.5e-3, are accepted.
- Select the unit to convert from and the unit to convert to.
- The result is shown instantly with the same value in all other supported units. Press Convert Now if you want to confirm manually.
- Use Swap Units to reverse, Scientific notation for extreme values, Copy Result to copy, or Reset to start again.
Illumination cannot be negative. A value of zero is valid and means no light.
Practical Examples
- Office lighting: a recommended 500 lx desk level equals 46.45152 fc.
- US specification: a requirement of 30 fc is 322.917312501 lx.
- Daylight: 25,000 lx = 25 klx.
- Phot: 0.5 phot = 0.5 × 10,000 = 5,000 lx.
- Dim light: 250 nox = 250 × 0.001 = 0.25 lx.
Illumination – Common Values
Quick reference for frequently used conversions
| Lux (lx) | Kilolux (klx) | Foot-candle (fc) | Phot (ph) | Nox |
|---|---|---|---|---|
| 0.25 | 0.00025 | 0.02322576 | 0.000025 | 250 |
| 1 | 0.001 | 0.09290304 | 0.0001 | 1,000 |
| 10 | 0.01 | 0.9290304 | 0.001 | 10,000 |
| 50 | 0.05 | 4.645152 | 0.005 | 50,000 |
| 100 | 0.1 | 9.290304 | 0.01 | 100,000 |
| 300 | 0.3 | 27.870912 | 0.03 | 300,000 |
| 500 | 0.5 | 46.45152 | 0.05 | 500,000 |
| 1,000 | 1 | 92.90304 | 0.1 | 1,000,000 |
| 10,000 | 10 | 929.0304 | 1 | 10,000,000 |
| 100,000 | 100 | 9,290.304 | 10 | 100,000,000 |
Real-Life Applications of Illumination Conversion
- Workplace and school lighting: standards give target lux levels for offices, classrooms and workshops. Many European standards use lux while US documents use foot-candles.
- Photography and film: light meters read in lux or foot-candles, and exposure guides may use either.
- Architecture and lighting design: calculations and drawings from different countries need unit conversion.
- Horticulture and indoor growing: light levels for plants are often compared in lux and foot-candles.
- Safety and emergency lighting: escape route minimums are written in lux or foot-candles.
- Astronomy and night vision: very low light levels are expressed in millilux or nox.
Rough guide: a clear full moon gives about 0.1 to 0.3 lx, typical office lighting about 300 to 500 lx, and bright daylight in the shade can reach tens of thousands of lux. These are typical values and vary with conditions.