UnitSnapIlluminance converter
Illuminance measures how much visible light falls on a surface per unit area. The SI unit is the lux, equal to one lumen per square meter; the older name meter-candle means the same thing. Illuminance is weighted by the sensitivity of the human eye, so it describes perceived brightness on a surface, not total radiant energy.
Convert between 7 illuminance units. Pick any two units below; results update as you type.
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About illuminance units
In the US, lighting designers often use the foot-candle, one lumen per square foot, which is roughly 10.76 lux. The phot, a CGS unit, is one lumen per square centimeter, exactly 10,000 lux. Typical office lighting targets are a few hundred lux, while direct sunlight can exceed 100,000 lux.
Illuminance is different from luminous flux, measured in lumens, which is the total light output of a source such as a bulb. The same lamp produces lower illuminance on a surface that is farther away or spread over a larger area.
Tips
- Bulb packaging lists lumens (total output); light meters measure lux or foot-candles at a specific spot.
- For a point source, illuminance falls with the square of distance, so doubling the distance gives roughly one quarter of the light.
- When reading lighting standards, confirm whether targets are in lux or foot-candles, which differ by about a factor of 10.
All illuminance units
| Unit | Symbol | Value in lux |
|---|---|---|
| Lux | lx | 1 lx = 1 lx |
| Lumens per Square Meter | lm/m² | 1 lm/m² = 1 lx |
| Meter-Candles | m·cd | 1 m·cd = 1 lx |
| Lumens per Square Foot | lm/ft² | 1 lm/ft² = 10.76391 lx |
| Foot-Candles | fc | 1 fc = 10.76391 lx |
| Lumens per Square Centimeter | lm/cm² | 1 lm/cm² = 10,000 lx |
| Phots | ph | 1 ph = 10,000 lx |
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Factors: NIST SP 811 · SI Brochure · NIST Handbook 44 — Updated