| Definition: | SI unit of luminous intensity, taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, to be 683 when expressed in the unit lm W−1
Note 1 to entry: The definition in the SI Brochure is: "The candela, symbol cd, is the SI unit of luminous intensity. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, to be 683 when expressed in the unit lm W−1, which is equal to cd sr W−1, or cd sr kg−1m−2 s3, where the kilogram, metre and second are defined in terms of h, c and ΔνCs."
Note 2 to entry: This definition applies to photopic vision, mesopic vision and scotopic vision.
Note 3 to entry: The candela is one of the seven SI base units: second (s), metre (m), kilogram (kg), ampere (A), kelvin (K), mole (mol) and candela (cd).
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