The illuminance produced by one lumen spread over one square foot, equal to about 10.76 lux. North American designers, codes and owners talk in foot-candles: around 30 to 50 fc for offices, 5 fc or less for parking, 1 fc at a property line for some ordinances. Calculation software and meters switch freely between the two units, which is a common source of reporting mistakes.
Parking lot averages 2.1 foot-candles with a max to min of 12 to 1, inside what the city asks for.
Also heard as
- fc
- footcandle
- ft-c
Related terms
Lux
The metric measure of light landing on a surface: one lumen falling evenly on each square meter.
Illuminance
The amount of light falling on a surface per unit area, measured in lux or foot-candles.
Uniformity
How evenly light is spread over an area, expressed as a ratio such as minimum to average or maximum to minimum.
Point-by-point
A lighting calculation that predicts illuminance at each point on a grid from every luminaire's photometric data.