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IEVref: | 112-02-10 | ID: | |

Language: | en | Status: Standard | |

Term: | candela | ||

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Symbol: | cd | ||

Definition: | SI unit of luminous intensity, equal to the luminous intensity in a given direction, of a source that emits monochromatic radiation of frequency 540 × 10^{12} Hz and has a radiant intensity in that direction of 1/683 W/sr
Note 1 to entry: The definition in the SI Brochure is: "The candela, symbol 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 × 10 Note 2 to entry: This definition implies that 683 lm/W is the exact value of the luminous efficacy of monochromatic radiation 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). | ||

Publication date: | 2020-12 | ||

Source: | SI Brochure, 9th edition, 2019, 2.3.1, modified – The definition in the SI Brochure has been revised to comply with the IEV rules. Notes 1 to 3 to entry have been added. | ||

Replaces: | 112-02-10:2010-01 | ||

Internal notes: | 2020-12-10: Correction to Note 1 to entry: "minus" deleted in "monochromatic radiation of frequency 540 × 10−12 Hz". The French is already correct. JGO | ||

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Note 1 to entry: The definition in the SI Brochure is: "The candela, symbol 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 × 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}."

Note 2 to entry: This definition implies that 683 lm/W is the exact value of the luminous efficacy of monochromatic radiation *K*_{m}.

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).