https://doi.org/10.1351/goldbook.C00787
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 \(540\times 10^{12}\ \text{Hz}\), \(K_{cd}\), to be \(683\) when expressed in the unit \(\text{lm W}^{-1}\), which is equal to \(\text{cd sr W}^{-1}\), or \(\text{cd sr kg}^{-1}\ \text{m}^{-2}\ \text{s}^{3}\), where the kilogram, metre and second are defined in terms of @P04685@, @S05854-1@ and @S05854-2@.