Time evolution of the bolometric luminosity for different IMFs. The MKDP IMF changes with the initial mass of the UCD and does not scale linearly with its mass. In contrast, the vDC, SAL, and CAN IMFs have UCD-mass-independent slopes and scale proportionally with M_UCD. The grey panel shows the typical luminosities of quasars (Dunlop et al. 1993, 2003; Souchay et al. 2015) and the brown panel shows the luminosity span for the peak luminosities supernovae (Gal-Yam 2012; Lyman et al. 2016), which might cause luminosity variations in L_bol of UCDs younger than about 50 Myr according to SNe rates.