The SI unit of luminous intensity which is one of the seven fundamental SI units. It is defined as the luminous intensity n a given direction of a source that emits monochromatic radiation of frequency 540 THz and that has a radiant intensity in that direction of 1/683 watts per sterradian. The candela is abbreviated "cd."
The lumen is defined as 1 cd sterradian, and the lux is defined as 1 cd sterradian m-2.
Candle, Lumen, Luminous Intensity, Lux, Radiant Intensity
References
Bureau International des Poids et Mesures. "The International System of Units (SI), 7th ed." 1998. http://www1.bipm.org/en/si/si_brochure/.
