Originally comes from 1 fc being the illuminance on a surface 1 foot away from a 1 candela light source. A candela being roughly the intensity of light from a

Originally comes from 1 fc being the illuminance on a surface 1 foot away from a 1 candela light source. A candela being roughly the intensity of light from a candle. Intensity (candelas) breaking down to lumens per steradian. They're a measure of how bright a light is in a particular direction, rather than its total light output (which is lumens). And steradians, for the unfamiliar, being a measure of "solid angle". Steradians are to 3D angles as radians are to 2D angles. A 1 steradian solid angle projects out to an area of 1 unit^2 on the surface of a unit sphere. Fun stuff!