text: Within a homogeneous medium such as a solution, there is no scattering. For this case, researched extensively by August Beer, the concentration of the absorbing species follows the same linear contribution to absorbance as the path-length. Additionally, the contributions of individual absorbing species are additive. This is a very favorable situation, and made absorbance an absorption metric far preferable to absorption fraction (absorptance). This is the case for which the term "absorbance" was first used.
  A common expression of the Beer's law relates the attenuation of light in a material as:  where  is the absorbance;  is the molar attenuation coefficient or absorptivity of the attenuating species;  is the optical path length; and  is the concentration of the attenuating species.