## Wikipedia - Absorptance (en) absorptance, $$\alpha$$

https://doi.org/10.1351/goldbook.A00035
Ratio of the absorbed to the incident @R05046@. Also called @A00039@. When $$\alpha \leq 1$$, $$\alpha \approx A_{\text{e}}$$, where $$A_{\text{e}}$$ is the Napierian @A00028@.
Source:
Green Book, 2nd ed., p. 32 [Terms] [Book]