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Convert illuminance between metric and imperial units instantly
1 lux = 0.092903 foot-candles
foot-candles = lux × 0.092903
| Lux (lx) | Foot-Candles (fc) | Typical Application |
|---|---|---|
| 50 lx | 4.65 fc | Corridors, stairways |
| 100 lx | 9.29 fc | Casual reading |
| 200 lx | 18.58 fc | General office work |
| 500 lx | 46.45 fc | Detailed office work |
| 750 lx | 69.68 fc | Design, drafting |
| 1,000 lx | 92.90 fc | Supermarket displays |
| 1,500 lx | 139.35 fc | Detailed inspection |
| 2,000 lx | 185.81 fc | Surgery, precision work |
| 5,000 lx | 464.52 fc | TV/film production |
| 10,000 lx | 929.03 fc | Full daylight (not direct sun) |
| 50,000 lx | 4,645.15 fc | Bright sunlight |
| 100,000 lx | 9,290.30 fc | Direct sunlight |
Both lux and foot-candles measure illuminance - the amount of light falling on a surface. Lux is the metric unit (lumens per square meter), while foot-candles is the imperial unit (lumens per square foot). One lux equals 0.092903 foot-candles, or conversely, one foot-candle equals 10.764 lux. These units are essential for lighting design, workplace safety compliance, photography exposure calculations, and architectural specifications. Unlike lumens which measure total light output from a source, illuminance measures the intensity of light at a specific location, decreasing with distance from the source. Professional lighting designers and photographers use light meters calibrated in lux or foot-candles to ensure proper illumination levels for various applications, from office environments to film sets.
Foot-candles originated in the United States and remain common in American lighting standards, while lux is the SI (metric) unit used internationally. The difference stems from the area unit: foot-candles use square feet while lux uses square meters. Since 1 square meter equals 10.764 square feet, the conversion factor between these units is 10.764. Most modern light meters can display both units.
Comfortable reading requires 300-500 lux (30-50 fc) for most people, though this increases with age. For prolonged reading or detailed work, 500-750 lux (50-75 fc) is recommended. Task lighting can supplement ambient lighting to achieve these levels at specific work surfaces without over-illuminating the entire room. The Illuminating Engineering Society (IES) provides detailed recommendations for various activities.
Yes, illuminance follows the inverse square law: doubling the distance reduces illuminance to one-quarter. For example, if a surface receives 1,000 lux at 1 meter from a point source, it receives only 250 lux at 2 meters. This is why lighting calculations must account for fixture height and distance to work surfaces. Diffuse sources and reflective surfaces complicate this relationship in real-world environments.
Lumens measure total light output from a source, while lux measures illuminance at a specific surface. Think of lumens as the total water flowing from a hose, and lux as how wet a particular spot gets. A 1,000-lumen light source creates different lux levels depending on distance and spread: concentrated in a spotlight it might produce 5,000 lux in a small area, but diffused over a room might only produce 100 lux on work surfaces.
Yes, the conversion factor (0.092903) is purely geometric and doesn't depend on light color, spectrum, or color temperature. However, human perception of brightness varies with color - we're most sensitive to yellow-green light (555nm). This is why photometric measurements (lux/foot-candles) use spectral weighting to match human vision. The conversion between lux and foot-candles remains constant regardless of these factors.
Most building codes and workplace standards specify minimum illuminance levels with some tolerance. Measurements within ±10% are generally acceptable for compliance purposes. Professional light meters have ±2-5% accuracy under controlled conditions. However, natural variations in lamp output, aging, dirt accumulation, and surface reflectance mean actual illuminance varies over time, so designs typically include a maintenance factor providing 20-30% excess initial lighting.