The Globular Cluster Luminosity Function (GCLF) is an observed density function of the occurrence of Globular Clusters at various B-Band Absolute Magnitudes. The distribution peaks at about absolute Magnitude -6.5. This is taken as a distance indicator for galaxies: by assembling a histogram of globular clusters in a galaxy by Apparent Magnitude, the absolute magnitude, and thus the distance of some of them can be inferred.
Luminosity Function (LF)
Planetary Nebula Luminosity Function (PNLF)