footcandle

The footcandle is a unit of illuminance, a measure of how much luminous flux falls on a surface. It is equivalent to one lumen per square foot. The footcandle is part of the imperial system of units and is less commonly used today than the SI unit, the lux, which is equivalent to one lumen per square meter. One footcandle is approximately equal to 10.764 lux.

The concept of the footcandle originated from the idea of measuring light intensity based on the light produced by a standard candle. Specifically, it was defined as the illuminance received by a surface placed one foot away from a standard candle. While this definition provides a historical context, modern measurement is done with light meters that directly quantify the illuminance in footcandles or lux.

Footcandle measurements are useful in various applications, including architectural lighting design, workplace safety, and photography. For instance, recommended illuminance levels for different tasks are often specified in footcandles to ensure adequate visibility and prevent eye strain. While the lux is the internationally recognized standard, the footcandle can still be encountered in older documents or in regions that traditionally use imperial units. The conversion between footcandles and lux is straightforward, allowing for easy comparison between measurements made in different systems.