Full continuum and spectral line flux emitted by a model clump of M = 10 M_⊙, n = 10⁵ cm^-3, and χ = 1000. The two panels show the results for different dust models. Top: WD01-7 dust model, equivalent to a R_V = 3.1. This is the dust model with the largest grain surface contributing to the heating. Bottom: MRN dust mode. This is a dust model with a slightly smaller grain surface compared to WD01-7. The PE heating was calculated according to Bakes & Tielens (1994).