absorbance (quality) true PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) absorbance Absorbance is the logarithm of the ratio of intensities of electromagnetic radiation on both sides of a medium that the radiation passes through. Lambert-Beer's law states that absorbance is equal to the product of molar coefficient of absorbance of an absorbing compound in a medium times its concentration in the medium times path length of the electromagnetic radiation passing through the medium. [Allotrope] PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) absorbance (quality) optical quality