Exponents of the mass-luminosity relation of the form L ~ M^αμ^β for homogeneous stars from Gräfener et al. (2011), for a chemical composition corresponding to our ZAMS models (labelled with the subscript ZAMS), and for pure helium stars of the corresponding metallicity (labelled with the subscript TAMS). Here, μ is the mean molecular weight of the stellar gas, which is computed as 1 /μ = 2X + 0.75Y + 0.5Z, with X, Y, and Z being the hydrogen, helium, and metal mass fraction, and assuming complete ionization.