depth of penetration of light

The inverse of the absorption coefficient. If the decadic absorption coefficient, $Math - text$ , is used, the depth of penetration ( $Math - ei$ ) is the distance at which the radiant power, $Math - text$ , decreases to one tenth of its incident value, $Math - text$ . If the Naperian absorption coefficient, $Math - text$ , is used, the depth of penetration ( $Math - ei$ in this case) is the distance at which the radiant power decreases to $Math - ei$ of its incident value.

See: absorbance, attenuance

Source:

PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2235