Free Illumination Converter
Convert illumination units instantly — lux, foot-candle, phot, kilolux, millilux, lumen/m², W/m². Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Illuminance is measured as luminous flux per unit area: 1 lux = 1 lumen per square meter by definition, while 1 foot-candle = 10.76391 lux (the ratio between a square meter and a square foot). Because foot-candles are defined per square foot rather than per square meter, the conversion factor isn't a clean round number — it's simply the area-conversion ratio applied to a light-measurement unit.
Practical Real-World Scenarios
- Architectural and interior lighting design: building codes and lighting specifications use lux internationally but foot-candles remain common in US commercial lighting standards.
- Photography and film production: light meters can display either unit, and cinematographers working across international crews need to convert on set.
- Agriculture and horticulture: grow-light intensity for indoor farming is specified in lux or the related PPFD units, with foot-candles appearing mainly in older US equipment manuals.
Historical & Technical Background
The lux was adopted as the SI-derived unit for illuminance in the mid-20th century, built from the lumen (a measure of total visible light output) divided by area. The foot-candle predates it, originally defined in the 19th century as the illuminance produced by one candle at one foot's distance — a delightfully literal, pre-electric definition that has persisted in US lighting standards long after standard candles stopped being the practical reference.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience. “W/m² (555 nm only)” uses 683 lm/W and is valid only for monochromatic green light at 555 nm; it is not a general watt-to-lux conversion.
How This Converter Works
Illumination (illuminance) measures the amount of light falling on a surface. Lux is the SI standard, foot-candles are used in the US film and photography industry. Our converter handles 10 illumination units.
Common Conversions
| Lux (lx) | Foot-candle (fc) | Context |
|---|---|---|
| 0.001 lx | 0.0001 fc | Moonless night sky |
| 1 lx | 0.093 fc | Deep twilight (full moon ≈ 0.1–0.3 lx) |
| 400 lx | 37.2 fc | Office lighting standard |
| 1,000 lx | 92.9 fc | TV studio lighting |
| 10,000 lx | 929 fc | Overcast outdoor daylight |
| 100,000 lx | 9,290 fc | Direct sunlight |