Mean values of the fraction of the luminosity of the old and the young stellar populations (left and right panel, respectively) used for the dust heating. The crossed bars show the mean values of the ratio of the dust-absorbed luminosity to the unattenuated luminosity of the corresponding stellar component, while the solid bars are the ratios of the attenuated luminosity of the specific stellar component to its unattenuated luminosity. In each panel, the ratios are presented for each of the three galaxy populations (ETGs, LTGs, and (U)LIRGs) in the leftmost sub-panel, and for the four merging classes in the rightmost sub-panel.