candela (cd)

Document v1 · published by Koskamo · updated 2026-10-05

The candela (symbol cd) is the SI base unit of luminous intensity, per the BIPM SI Reference Point.

Name: candela
Symbol: cd
Unit type: SI base unit
Quantity kind: luminous intensity
Definition (status current, in force since 2019-05-20): The candela, symbol $\rm{cd}$, 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 ${540 \times 10^{12}}\ {{\rm{Hz}}}$, ${K_{\rm{cd}}}$, to be ${683}$ when expressed in the unit ${\rm{lm}}\ {\rm{W}}^{-1} $, which is equal to ${\rm{cd}}\ {\rm{sr}}\ {\rm{W}}^{-1}$, or ${\rm{cd}}\ {\rm{sr}}\ {\rm{kg}}^{-1}\ {\rm{m}}^{-2}\ {\rm{s}}^{3}$, where the kilogram, metre and second are defined in terms of ${h}$, $c$ and $\Delta\nu_{\rm{Cs}}$.
Defining constant: luminous efficacy (fixed numerical value 683)
Defining equation: 1\;{\rm{cd}} = \left(\frac{{K_{\rm{cd}}}}{683}\right) {\rm{kg}}\;{\rm{m}}^2\;{\rm{s}}^{-3}\;{\rm{sr}}^{-1}
Defining resolution: https://si-digital-framework.org/bodies/CGPM#CGPM26-Res1
Superseded definitions: candela1948 (1948-01-01 to 1967-10-12); candela1967 (1967-10-13 to 1979-10-10); candela1979 (1979-10-11 to 2019-05-19)

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Original source: si-digital-framework.org
Published on Koskamo by: Koskamo
Citation version: Document v1
Reuse: BIPM SI Reference Point (si-digital-framework.org), the SI defining constants, base and derived units, and prefixes; CC BY 3.0 IGO

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The candela (symbol cd) is the SI base unit of luminous intensity, per the BIPM SI Reference Point.

- Name: candela
- Symbol: cd
- Unit type: SI base unit
- Quantity kind: luminous intensity
- Definition (status current, in force since 2019-05-20): The candela, symbol $\rm{cd}$, 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 ${540 \times 10^{12}}\ {{\rm{Hz}}}$, ${K_{\rm{cd}}}$, to be ${683}$ when expressed in the unit ${\rm{lm}}\ {\rm{W}}^{-1} $, which is equal to ${\rm{cd}}\ {\rm{sr}}\ {\rm{W}}^{-1}$, or ${\rm{cd}}\ {\rm{sr}}\ {\rm{kg}}^{-1}\ {\rm{m}}^{-2}\ {\rm{s}}^{3}$, where the kilogram, metre and second are defined in terms of ${h}$, $c$ and $\Delta\nu_{\rm{Cs}}$.
- Defining constant: luminous efficacy (fixed numerical value 683)
- Defining equation: 1\;{\rm{cd}} = \left(\frac{{K_{\rm{cd}}}}{683}\right) {\rm{kg}}\;{\rm{m}}^2\;{\rm{s}}^{-3}\;{\rm{sr}}^{-1}
- Defining resolution: https://si-digital-framework.org/bodies/CGPM#CGPM26-Res1
- Superseded definitions: candela1948 (1948-01-01 to 1967-10-12); candela1967 (1967-10-13 to 1979-10-10); candela1979 (1979-10-11 to 2019-05-19)

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Published by Koskamo2026-10-05
Version 1