What does (blank) foot candles, mean?? Please Help!

[OrchidDragon]

Hi I'm confused..I've been growing orchids for about..3-4 years now, and I keep seeing that the way people measure an Orchid's light is by "foot candles"...Ok, so I know they're not ACTUALLY candles but what are they? For instance, about three months ago I bought a Lady of The Night (Brassavola nodosa), and I read that they need 2500 - 3500 foot candles. How do I which window in my house has that? I guess what I'm asking is for someone to explain this form of measurement..in depth. Sorry for sounding so stupid..I'm only 15. Thanks!



(P.S. I've successfully grown orchids for the past 3-4 years, but I still would like to know how to use this measurement. Otherwise, I'm just going to have to keep being "successful", with Orchids by chance.)