Top: blackbody-estimated luminosities, L_bb, versus temperature, T_bb, determined from Planck functions fitted to the continuum component of SSa and SSe spectra, marked by bullet and triangular symbols, respectively. Open symbols indicate particularly high degree of uncertainty owed to line blends or high but poorly constrained amounts of photoelectric absorption. The hatched and shaded histograms in the top and right, decoded in the legend, give the number of SSe and SSa spectra in rough temperature and luminosity intervals. Bottom: cumulative distributions of derived luminosities for SSa and SSe, including only the systems with filled symbols in the top panel. SSa clearly yield higher luminosities. BB-derived luminosities and temperatures are indicative, as they are not the result of a full-physics modelling of the data, and for this reason error bars are not plotted.