Foot-candle (fc)
In photography we often use the term foot-candle. It is the amount of illumination the inside surface of a 1-foot radius sphere would be receiving if there were a uniform point source of one candela in the exact center of the sphere. Some people simplify this definition by stating that it is the intensity of one candle one foot away from the source. This measures the perceived intensity. How intense is the light at a certain distance; in other words its illuminance.