https://doi.org/10.1351/goldbook.D01605

The inverse of the absorption coefficient. If the decadic absorption coefficient, a, is used, the depth of penetration (1/a) is the distance at which the radiant power, P λ, decreases to one tenth of its incident value, P λ 0. If the Naperian absorption coefficient, α, is used, the depth of penetration (1/α = β in this case) is the distance at which the radiant power decreases to 1/e of its incident value.*See: *absorbance, attenuance*Source: *

PAC, 1996,*68*, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2235 (https://doi.org/10.1351/pac199668122223)

PAC, 1996,