In glassy polymers toughened by inclusion of nanometric rubber particles, the high impact strength is due to cavitation of the rubber particles followed by the appearance of microshear bands in the glassy matrix. These materials are mostly opalescent or even opaque, which renders difficult any optical investigation of the damage process. Simple light scattering techniques were employed in earlier work to study the onset of damage in transparent toughened polymers. As demonstrated in one previous paper, multiple Light scattering can be employed to further investigate opaque materials and hence highly damaged polymers. Coherent light backscattering in strongly opaque materials arises from the fact that an incident light beam, if not absorbed, is scattered successively by several scatterers before emerging again at the front surface of the body. The so-called coherent backscattering cone may be analyzed in terms of the size, shape, and density of the scatterers. In the present work, this technique was applied to a semicrystalline polymer and to rubber toughened PMMA containing core-shell (hard core) particles, an initially transparent material which becomes progressively opaque in the course of mechanical damage under stress. During the damage process, both the number of cavitated particles and their individual void fraction may increase, and a cavitated particle acts as a light scatterer of cross-section proportional to its void content. The weakness of such scattering techniques resides in the fact that the light scattering pattern is determined by the product of the density of the scatterers and their scattering cross-section. Consequently, the number of damaged particles cannot be separated from the particle void content. This study describes a new method based on the superposition of small elastic unloadings on the main tensile strain. During these unloadings, the number of damaged particles remains constant but their optical cross-section changes, thus leading to a supplementary equation describing the scattering properties of the body. Hence, the number of cavitated particles and their individual void fraction may be calculated separately from the experimental data. Since the use of coherent light backscattering to investigate damage mechanisms in polymers is relatively new, the paper also recalls the basic principles of multiple light scattering.