depth of penetration

of light
https://doi.org/10.1351/goldbook.D01605
The inverse of the @A00037@. If the decadic @A00037@, \(a\), is used, the depth of penetration (\(\frac{1}{a}\)) is the distance at which the @R05046@, \(P_{\lambda }\), decreases to one tenth of its incident value, \(P_{\lambda }^{0}\). If the Naperian @A00037@, \(\alpha \), is used, the depth of penetration (\(\frac{1}{\alpha } = \beta \) in this case) is the distance at which the @R05046@ decreases to \(\frac{1}{\text{e}}\) of its incident value.
See:
absorbance
,
attenuance
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2235 [Terms] [Paper]