a unit in which to measure
light visible to the
human eye.
selenium cell meters, when filtered, are often used to measure footcandles. i never heard of a foot
candle before i came to
miner institute; i suppose they are most commonly used among
scientists and
engineers. here we use them all the time to measure the light levels in the
cow barns.
cute story: in the early 40's, companies like
general electric came out with meters that supposedly measured
black light in footcandles. however, since footcandles are only a measurement of visible light, we can see this as a
scientific inaccuracy put up with for the sake of convenience.
http://www.magwerks.com/Information/footcandles_vs_mW.htm really knows its footcandles...