what is a footcandle a measure of
A foot candle is a measure of luminance or light intensity. It is an imperial measurement unit, unlike the more common lux, which is based on the International System of Units (SI) or metric system. Foot candles are mainly used in film and photography, but can also be used in gardening. One foot candle is the amount of illumination received on an area of a surface that is a sphere with a one foot radius, cast by a light source with an intensity of one candela.