[en] Divertor plasmas are a mixture of electrons, hydrogenic ions and neutrals and a radiation field. The strong mutual influence of the charged and neutral particle components is the key for establishing favourable divertor conditions, for example detached divertor scenarios. In most quantitative assessments of such plasmas the radiation field has been regarded as entirely decoupled from the particle fields, i.e., the plasma is assumed to be optically thin. However, various spectroscopic studies have shown clear signals of opacity (line absorption) effects. In order to quantify these effects we argue that already current divertor neutral particle codes, in which photons are treated as just another particle species, can be used. We apply this concept to study possible Lyman opacity effects on divertors