The candela, symbol \(\text{cd}\), is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 x 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, metre and second are defined in terms of h, c and Δν_Cs.