In the first part of this work a simple model for the description of the radiant Field in heterogeneous photoreactors was developed, based on the assumption of zero reflectance of the particles. In this second part of the investigation a limiting model is developed in which the above hypothesis is removed. In this last model, scattering phenomena are dealt with. in a very simple "two-flux" way, so that analytical solutions are obtained again. The case here developed is the same as in pari; 1, namely slab geometry with orthogonal parallel irradiation, giving special reference to the important case of semi-infinite reactor thickness. Both cases of solid catalysts with single particle size and with distributed particle sizes are implicitly dealt with. The model here developed represents a limiting case as it overestimates the radiation lost from the reactor, giving rise to an opposite behavior with respect to the predictions given by the simpler model developed in part P. Therefore, the real behavior of heterogeneous photoreactors lies between the predictions of the two models. It is also shown that for a fairly wide range of reflectance values, the predictions of the two models do not differ significantly.