Ṁ_SED–luminosity relations for the four open clusters RSGC1, NGC 2100, NGC 7419, and χ Per. The coloured open symbols represent the (L_bol, Ṁ_SED)-values for the four clusters studied by Beasor & Davies (2016) and Beasor et al. (2020); error bars indicate their most conservative error estimates (see Appendix E). The dashed lines in the left panel show the individual fits to Eq. (4) where the values of both a and b are free parameters in each fit. In the right panel, we force the slope b to be identical for all clusters and fit Eq. (5). The best-fit values are listed in the legend and in Table 2. The shaded areas provide a visualisation of the uncertainties of the fits. They were constructed through MC as the 68%-locus of all best-fit relations derived from a fit to mock data sets used to assess the errors on the best-fit parameters.