Defined in 1996 by the "Conférence Générale des Poids et Mesures" (CGPM, the 11th General Conference on Weights and Measures), "the candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian."