Total luminosity function of the GC candidates over the joint sample of UDGs and LSB galaxies (Table 3) with N_GC ≥ 0 within 1.5R_e normalized to the total galaxy area (solid blue line). Left: GCLF globally corrected. The density distribution for the global background is shown with green dotted line. The gray shaded histogram shows the residuals of the two. The solid line shows the best-fit Gaussian function of the GC luminosity function (gray bins). The best-fit parameters are: μ_g, TOM = 25.8 ± 0.3 mag, σ_GCLF = 0.69 ± 0.12 mag. Right: As left panel, but using the local background (red dot-dashed line). The best-fit parameters are: μ_g, TOM = 25.8 ± 0.2 mag, σ_GCLF = 0.66 ± 0.14 mag. The error bars show the uncertainties on the residual GC density calculated as detailed in Sect. 4.