ABSTRACT:  The effect of polydispersity on extinction cross sections is studied for a particle system composed of coated, spherical particles. Aden-Kerker equatuons, governing the light-scattering behaviour of the system, are formulated in a way that makes them more suitable for computation purposes. Differences found between light scattered by non-absorbing and highly absorbing particles show the importance of using accurate refractive indices, especially when dealing with their imaginary part, which accounts for absorption.