Luminosity function of all spectroscopically confirmed PNs corrected for incompleteness (full dots). The dashed green line represents the Ciardullo et al. (1989) formula for a distance modulus of 30.8, convolved with photometric errors and normalised to the data at the bright end. The spectroscopically confirmed PNLF shows an excess of fainter PNs with respect to the analytical formula, similar to the photometric PNLF (Longobardi et al. 2013). Open circles represent magnitude bins where the sample is not completeness-corrected. The error bars show the uncertainties from counting statistics and completeness correction.