05045 IUPAC Gold Book - radiant intensity 10.1351/goldbook.R05045 R05045 current quantity 1 Radiant power, \(P\), at all wavelengths per solid angle, \(\varOmega\). The @R05046-2@ emitted in a given direction by a source or an element of the source in a small cone containing the given direction divided by the solid angle of the cone. SI unit is \(\rm{W sr}^{-1}\). Mathematical definition: \(I = \rm{d}P/\rm{d}\varOmega\). If the radiant power is constant over the solid angle considered, \(I = P/\varOmega\). Equivalent to \(I = \int_{\lambda}I_{\lambda}\, \rm{d}\lambda\), where \(I_{\lambda}\) is the spectral radiant intensity at wavelength \(\lambda\). It is not recommended to abbreviate this term to just intensity because it is confusing. angle https://goldbook.iupac.org/terms/view/A00346 radiant power https://goldbook.iupac.org/terms/view/R05046 spectral radiant intensity https://goldbook.iupac.org/terms/view/S05827 wavelength https://goldbook.iupac.org/terms/view/W06659 PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 410 (https://doi.org/10.1351/pac200779030293) https://goldbook.iupac.org/terms/view/R05045/html https://goldbook.iupac.org/terms/view/R05045/json https://goldbook.iupac.org/terms/view/R05045/plain Citation: 'radiant intensity' 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.R05045 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-05-10T15:55:10+00:00