Term: action spectrum
https://doi.org/10.1351/goldbook.A00088

Definition:
A plot of a relative biological or chemical photoresponse (= Δ 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:
1) excitation spectrum (http://doi.org/10.1351/goldbook.E02253).
2) efficiency spectrum (http://doi.org/10.1351/goldbook.E01908).
3) wavelength (http://doi.org/10.1351/goldbook.W06659).
4) radiant power (http://doi.org/10.1351/goldbook.R05046).
5) spectral responsivity (http://doi.org/10.1351/goldbook.S05829).
6) spectral or quantum effectiveness (http://doi.org/10.1351/goldbook.S05814).
7) quantum efficiency (http://doi.org/10.1351/goldbook.Q04988).

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

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. https://doi.org/10.1351/goldbook.A00088

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