  We have measured the 3.6 micron luminosity evolution of about 1000 galaxies
in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity
evolution, i.e. in a logically rigorous way. We find that the luminosity of our
galaxies evolves as an old and passively evolving population formed at high
redshift without any need for additional redshift-dependent evolution. Models
with a prolonged stellar mass growth are rejected by the data with high
confidence. The data also reject models in which the age of the stars is the
same at all redshifts. Similarly, the characteristic stellar mass evolves, in
the last two thirds of the universe age, as expected for a stellar population
formed at high redshift. Together with the old age of stellar populations
derived from fundamental plane studies, our data seems to suggest that
early-type cluster galaxies have been completely assembled at high redshift,
and not only that their stars are old. The quality of the data allows us to
derive the LF and mass evolution homogeneously over the whole redshift range,
using a single estimator. The Schechter function describes the galaxy
luminosity function well. The characteristic luminosity at z=0.5 is is found to
be 16.30 mag, with an uncertainty of 10 per cent.
