The candela, symbol \(\pu{cd}\), 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 \(\pu{540E12 Hz}\), \(K_{\rm{cd}}\), to be \(683\) when expressed in the unit \(\pu{lm W^{-1}}\), which is equal to \(\pu{cd sr W^{-1}}\), or \(\pu{cd sr kg-1 m-2 s3}\), where the kilogram, metre and second are defined in terms of h, c and Δν_Cs.