Foot-candle is a unit of measurement of illumination, the amount of light that falls on an object. The foot-candle is part of the inch-pound system of measurement customarily used in the United States.
Two factors determine the amount of light an object receives: (1) the luminous intensity (the amount of light a light source produces) and (2) the distance between the light source and the object. As the luminous intensity increases, illumination also increases. As the distance increases, illumination decreases by the square of the distance.
To calculate in foot-candles the illumination (E) on a surface perpendicular to a light ray, scientists use the formula E = I/D< 2. I is the luminous intensity in candelas (see Candela). D is the distance in feet between the light source and the object.
In the metric system, illumination is measured in a unit called the lux. Distance is measured in meters. One foot-candle equals 10.764 lux.
