text: For samples which scatter light, absorbance is defined as "the negative logarithm of one minus absorptance (absorption fraction: ) as measured on a uniform sample". For decadic absorbance, this may be symbolized as  If a sample both transmits and remits light, and is not luminescent, the fraction of light absorbed  remitted  and transmitted  add to 1:  Note that  and the formula may be written as  For a sample which does not scatter,  and  yielding the formula for absorbance of a material discussed below. 
  Even though this absorbance function is very useful with scattering samples, the function does not have the same desirable characteristics as it does for non-scattering samples. There is, however, a property called absorbing power which may be estimated for these samples. The absorbing power of a single unit thickness of material making up a scattering sample is the same as the absorbance of the same thickness of the material in the absence of scatter.