Mean interstellar radiation field assumed to model the SEDs of embedded cores. The solid black line is the ISRF caused by the stellar light as provided by Mathis et al. (1982). The dark grey line shows the assumed angle-averaged dust re-emission. The contribution of the PAH emission is reduced relative to the dust re-emission of the diffuse ISM (Fischera, in prep.) shown as light grey curve. The strength of the radiation field is scaled to the DIRBE flux at 140   μm. The DIRBE fluxes at 100, 140, and 240   μm are shown as open diamonds. The dust emission is divided into its several components: PAH (long dashed line), graphite (short dashed line), silicate (dotted line), and iron (dashed-dotted line).