Title: action spectrum
Long Title: IUPAC Gold Book - action spectrum
DOI: 10.1351/goldbook.A00088
Status: current

Definition
A plot of a relative biological or chemical photoresponse (= \(\Delta y\)) per number of incident photons against wavelength or energy of radiation under the same radiant power of light. This form of presentation is frequently used in the studies of biological or solid state systems, where the nature of the absorbing species is unknown. This type of action spectrum is sometimes called spectral responsivity or sensitivity spectrum. The precise action spectrum is a plot of the spectral or quantum effectiveness. By contrast, a plot of the biological or chemical change or response per absorbed photon (quantum efficiency) versus wavelength is the efficiency spectrum.

Related Terms
- efficiency spectrum: https://goldbook.iupac.org/terms/view/E01908
- excitation spectrum: https://goldbook.iupac.org/terms/view/E02253
- quantum efficiency: https://goldbook.iupac.org/terms/view/Q04988
- radiant power: https://goldbook.iupac.org/terms/view/R05046
- spectral or quantum effectiveness: https://goldbook.iupac.org/terms/view/S05814
- spectral responsivity: https://goldbook.iupac.org/terms/view/S05829
- wavelength: https://goldbook.iupac.org/terms/view/W06659

Source
- PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2227 (https://doi.org/10.1351/pac199668122223)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00088/html
- json: https://goldbook.iupac.org/terms/view/A00088/json
- xml: https://goldbook.iupac.org/terms/view/A00088/xml

Citation: Citation: 'action spectrum' 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.A00088
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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: 2026-06-30T19:42:42+00:00