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The Illumination Converter converts between units of illuminance, which measures the amount of luminous flux incident on a surface per unit area. The SI unit is the lux (lx), defined as one lumen per square meter (lm/m²), while the imperial equivalent is the foot-candle (fc), equal to one lumen per square foot.
Illuminance is critical in lighting design, workplace safety, photography, horticulture, and architectural planning. Building codes and occupational health standards specify minimum illuminance levels for various tasks: 300–500 lux for general office work, 750–1,000 lux for detailed technical work, and 50–100 lux for corridors and storage areas.
The relationship between lux and foot-candles is based on the area conversion: 1 ft² = 0.0929 m², so 1 foot-candle = 10.7639 lux. The phot is a CGS unit (1 phot = 10,000 lux), and the nox is used for very low light levels (1 nox = 0.001 lux), such as starlight and moonlight measurements.
Outdoor illuminance varies enormously: direct sunlight provides 100,000–130,000 lux, an overcast day about 10,000–20,000 lux, twilight about 10 lux, a full moon about 0.25 lux, and starlight about 0.001 lux (1 nox).
For photography, illuminance determines correct exposure settings. Indoor scenes typically range from 100 to 1,000 lux, requiring larger apertures or higher ISO compared to outdoor scenes at 10,000–100,000 lux.
All values are normalized to lux (lx). Key conversions: 1 fc = 10.7639 lx (from 1 ft² = 0.092903 m²), 1 phot = 10,000 lx, 1 nox = 0.001 lx, 1 mlx = 0.001 lx, 1 klx = 1,000 lx.
Recommended illuminance levels: reading: 300–500 lx, office work: 500 lx, surgery: 10,000–100,000 lx, warehouse: 100–200 lx, outdoor parking: 10–50 lx.
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500 lx = 46.45 fc (office lighting)
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50 fc = 538.2 lx
A lux (lx) is the SI unit of illuminance, equal to one lumen per square meter. It measures how much luminous flux falls on a surface.
Divide lux by 10.7639. For example, 500 lx = 46.45 foot-candles.
A foot-candle (fc) is the illuminance produced by one lumen uniformly distributed over one square foot. 1 fc = 10.7639 lux.
EN 12464-1 and IES recommend 500 lux (about 46 foot-candles) for general office work, 300 lux for filing areas, and 750 lux for technical drawing.
Direct sunlight produces 100,000-130,000 lux at the Earth's surface. An overcast day provides about 10,000-25,000 lux.
Lumens measure total light output from a source. Lux measures how much of that light falls on a surface (lumens per square meter). The same lumens spread over a larger area produce fewer lux.
The human eye can perceive light at levels as low as 0.001 lux (1 nox) under dark-adapted conditions. Normal vision functions well above 1 lux.
A phot (ph) is a CGS unit of illuminance equal to 10,000 lux (1 lumen per cm²). It is rarely used today but appears in older lighting references.
Use a light meter (lux meter or foot-candle meter) with a cosine-corrected sensor aimed at the surface where light falls. Many smartphone apps can provide approximate readings.
Illuminance decreases with the square of the distance from a point source: E = I/d², where E is lux, I is luminous intensity (candelas), and d is distance (meters).
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