text: The law can be expressed in terms of attenuation coefficient, but in this case is better called the Bouguer-Lambert's law.  The (Napierian) attenuation coefficient  and the decadic attenuation coefficient  of a material sample are related to its number densities and amount concentrations asrespectively, by definition of attenuation cross section and molar attenuation coefficient. Then the law becomesand
  In many cases, the attenuation coefficient does not vary with , in which case one does not have to perform an integral and can express the law as:where the attenuation is usually an addition of absorption coefficient  (creation of electron-hole pairs) or scattering (for example Rayleigh scattering if the scattering centers are much smaller than the incident wavelength). Also note that for some systems we can put  (1 over inelastic mean free path) in place of