Top panel: luminosity function of the spectroscopically confirmed halo PNs, corrected for incompleteness (red circles). The red line shows the fit of the generalised analytical formula (Eq. (10)) to the halo PNLF, with c₂ = 0.72 and bright cut-off at 26.3 mag, corresponding to a distance modulus m − M = 30.8. Central panel: completeness-corrected PNLF for the ICPNs (blue circles). The blue line shows the fit of the generalised analytical formula (Eq. (10)) to the ICPNLF, with c₂ = 0.66. The ICPNLF shows a dip 1−1.5 mag fainter than the bright cut-off. Bottom panel: PNLFs in absolute magnitude for the spectroscopically confirmed Virgo ICPNs (blue circles) and for the outer disk of M 33 (Ciardullo et al. 2004, cyan triangles) matched at the first bin. For this comparison, the data are corrected for line-of-sight reddening (see text). Absolute magnitudes are determined using a distance modulus of 30.8 for the ICL and 24.86 for M 33 (Ciardullo et al. 2004).