absorbance

symbols: $A$, $A_{10}$, $A_{\rm{e}}$
synonyms: extinction, optical density
https://doi.org/10.1351/goldbook.A00028
Logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls). Depending on the base of the logarithm a decadic and Napierian absorbance are used.
Note: This quantity is sometimes called 'extinction', although the term extinction, is reserved for the quantity which takes into account the effects of luminescence and scattering as well.
Source:
Green Book, 2nd ed., p. 32 [Terms] [Book]
See also:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2169 [Terms] [Paper]
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2226 [Terms] [Paper]
Citation: 'absorbance' 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.A00028 RIS BibTex EndNote
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