  The global star formation rate has decreased significantly since z ~ 1, for
reasons that are not well understood. Red-sequence galaxies, dominating in
galaxy clusters, represent the population that have had their star formation
shut off, and may therefore be the key to this problem. In this work, we select
127 rich galaxy clusters at 0.17<z<0.36, from 119 square degrees of the
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) optical imaging data, and
construct the r'-band red-sequence luminosity functions (LFs). We show that the
faint end of the LF is very sensitive to how red-sequence galaxies are
selected, and an optimal way to minimise the contamination from the blue cloud
is to mirror galaxies on the redder side of the colour-magnitude relation
(CMR). The LFs of our sample have a significant inflexion centred at Mr' ~-
18.5, suggesting a mixture of two populations. Combining our survey with low
redshift samples constructed from the Sloan Digital Sky Survey, we show that
there is no strong evolution of the faint end of the LF (or the red-sequence
dwarf-to-giant ratio) over the redshift range 0.2 < z < 0.4, but from z ~ 0.2
to z ~ 0 the relative number of red-sequence dwarf galaxies has increased by a
factor of ~3, implying a significant build-up of the faint end of the cluster
red-sequence over the last 2.5 Gyr.
