where "A" is the measured absorbance (in Absorbance Units (AU)), formula_2 is the intensity of the incident light at a given wavelength, formula_3 is the transmitted intensity, "L" the path length through the sample, and "c" the concentration of the absorbing species. For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, and has units of formula_4.