An Etymological Dictionary of Astronomy and Astrophysics

The → SI unit of → luminous intensity in a given direction; symbol cd. It is defined by taking the fixed numerical value of the → luminous efficacy of → monochromatic radiation of → frequency 540 × 10¹² Hz, K_cd, to be 683 when expressed in the unit lm W^-1, which is equal to cd sr W^-1, or cd sr kg^-1 m^-2 s³, where the kilogram, meter and second are defined in terms of → Planck’s constant (h), → velocity of light (c), and Δν_Cs.

See also: From L. candela, → candle.