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absorptance, \(\alpha\)

https://doi.org/10.1351/goldbook.A00035
Ratio of the absorbed to the incident radiant power. Also called absorption factor. When α ≤ 1, α ≈ Ae, where Ae is the Napierian absorbance.
Source:
Green Book, 2nd ed., p. 32 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)