Title: candela
Long Title: IUPAC Gold Book - candela
DOI: 10.1351/goldbook.C00787
Status: current
Index: unit

Definition
The candela, symbol \(\pu{cd}\), 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 \(\pu{540E12 Hz}\), \(K_{\rm{cd}}\), to be \(683\) when expressed in the unit \(\pu{lm W^{-1}}\), which is equal to \(\pu{cd sr W^{-1}}\), or \(\pu{cd sr kg-1 m-2 s3}\), where the kilogram, metre and second are defined in terms of h, c and ΔνCs.

Related Terms
- <em>h</em>: https://goldbook.iupac.org//terms/view/P04685
- Δ<em>ν</em><sub>Cs</sub>: https://goldbook.iupac.org//terms/view/S05854

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

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C00787/html
- json: https://goldbook.iupac.org/terms/view/C00787/json
- xml: https://goldbook.iupac.org/terms/view/C00787/xml

Citation: Citation: 'candela' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C00787
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-06-12T07:25:45+00:00