Candela (cd) is an SI Unit for luminous intensity in the International System of Units (SI). It is equal to the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. The name “candela” was introduced by Latinizing the name for a unit used at Leiden University, which was derived from the Latin candēla, meaning candle.