Absorption of Light by Turbid Materials

The transmission and absorption properties of turbid media have been examined with Kubelka and Munk’s theory of the optics of intensely scattering material. The equation for the optical density of such material as a function of thickness has been derived and examined experimentally. It is shown that the reflectivity and scattering coefficient can be determined absolutely without reference to a standard material from the optical-density measurements. The absorption spectra of pigments in scattering media and in clear solution have been compared. It is shown that light in passing through a turbid sample may traverse an optical path which is many times the sample thickness. The practical consequence of this increased path length is an intensification of the absorption bands of pigments in light-scattering media. The theoretical expression for this intensification has been derived and tested experimentally. Spectral effects due to the physical binding of pigment molecules to the scattering particles have also been examined.