  We present the composite luminosity function (hereafter LF) of galaxies for
81 Abell clusters studied in our survey of the Northern Hemisphere, using DPOSS
data processed by the CRoNaRio collaboration. The derived LF is very accurate
due to the use of homogeneous data both for the clusters and the control fields
and to the local estimate of the background, which takes into account the
presence of large-scale structures and of foreground clusters and groups. The
global composite LF is quite flat down to $M^*+5$ has a slope
$\alpha\sim-1.0\pm0.2$ with minor variations from blue to red filters, and
$M^*\sim-21.8,-22.0,-22.3$ mag ($H_0=50$ km s$^{-1}$ Mpc$^{-1}$) in the $g, r$
and $i$ filters, respectively (errors are detailed in the text). We find a
significant difference between rich and poor clusters thus arguing in favour of
a dependence of the LF on the properties of the environment.
