λQ_abs (left) and (right) are plotted versus the wavelength for 1 BG and for 1 BG with varying numbers of VSGs. The BG consist either of astronomical silicate a) or of amorphous carbon b). We consider 250, 500, 1000, 1500 and 2000 VSGs. In some cases Q_abs is not calculated at short wavelengths, since these calculations are time consuming. Calculations at short wavelengths are carried out for the cases where the dust temperature and emission is determined with DustEM. Since the optical constants of amorphous carbon are assumed to have an ambiguous power-law at wavelengths longward 300 μm we show the results only until 300 μm.