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 x 10^{12} 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} s^{3}, where the kilogram, metre and second are defined in terms of *h*, *c* and Δ*ν*_{Cs}.*Source: *

BIPM, The International System of Units, SI Brochure, 9^{th} ed. (2019), p. 135 (https://www.bipm.org/en/publications/si-brochure/)

BIPM, The International System of Units, SI Brochure, 9