A foot-candle (fc) is a unit of illuminance: one lumen of light falling on one square foot of surface. It is the customary way to measure light levels in the United States.
How foot-candles are measured
One foot-candle equals one lumen per square foot. In practice you measure it with a light meter held at the work plane — the desk, counter, or floor where the task happens.
Foot-candles versus lux
Lux is the metric equivalent. One foot-candle equals about 10.764 lux, so to convert foot-candles to lux you multiply by 10.764, and to go the other way you divide.
| Space | Typical level |
|---|---|
| Hallways | 5 to 10 fc |
| General office | 30 to 50 fc |
| Retail | 50 to 75 fc |
| Detailed work | 50 to 100 fc |
| Parking lot | 1 to 5 fc |
See the Foot Candle Calculator and the Recommended Foot Candle Levels.
Using foot-candles
A foot-candle is the imperial counterpart to lux: one lumen falling on one square foot. It’s still common in North American lighting specs and codes. Because a square foot is much smaller than a square metre, the numbers are smaller than lux for the same brightness — one foot-candle is about 10.76 lux. Typical targets in fc: ~5 fc for general circulation, 20–30 fc for offices and kitchens, 50 fc for detailed tasks, and 75+ fc for fine work. Like lux, foot-candles obey the inverse-square law, so illuminance drops to a quarter when you double the distance. To convert lux to foot-candles divide by 10.76; to go the other way, multiply.