In this research we present results of the studying and calculating the optically active range depth for diffuse light reflected coating at change of the dispersiveness of pigment grains used in coating and wavelength of incident electromagnetic radiation. This coating consists of zinc oxide powder and organic material that acts as a binding film. The size of zinc oxide powder grains were changed between 0.2 μm and 10 μm. In addition, the depths of optically active range of diffuse light reflected coating were calculated when the absorption coefficient of the pigment used in the ZnO/binder coating changed between -1 0.1cm and -1 1000cm . The obtained results allow us optimization of the diffuse light reflecting coatings thickness at preparation determined kinds of them.