  We carried out the deep spectroscopic observations of the nearby cluster
A2151 with AF2/WYFFOS@WHT. The caustic technique enables us to identify 360
members brighter than $M_r = -16$ and within 1.3$R_{200}$. We separated the
members into subsamples according to photometrical and dynamical properties
such as colour, local environment and infall time. The completeness of the
catalogue and our large sample allow us to analyse the velocity dispersion and
the luminosity functions of the identified populations. We found evidence of a
cluster still in its collapsing phase. The LF of the red population of A2151
shows a deficit of dwarf red galaxies. Moreover, the normalized LFs of the red
and blue populations of A2151 are comparable to the red and blue LFs of the
field, even if the blue galaxies start dominating one magnitude fainter and the
red LF is well represented by a single Schechter function rather than a double
Schechter function. We discuss how the evolution of cluster galaxies depends on
their mass: bright and intermediate galaxies are mainly affected by dynamical
friction and internal/mass quenching, while the evolution of dwarfs is driven
by environmental processes which need time and a hostile cluster environment to
remove the gas reservoirs and halt the star formation.
