of this term can also have an effect on the actual mass-luminosity relation, since we are using a counting method to obtain it. However, for the mass range we are interested in, the number counts are dominated by the central galaxies and will therefore not be affected (see section 4). Likewise, the only haloes capable of hosting subhaloes large enough to be counted in this range are the most massive ones, for which the effect is smallest (see section 3). Secondly, in principle, this approach will also depend on the exact form of the mass-luminosity relation. However, for the small deviations from the base relation we will be considering in this paper, the effect on the total luminosity is small, since the variation to the base relation will be greatest at higher mass, where this effect is smallest. We will therefore, for simplicity, use this one result throughout the paper.

Finally, it needs to be stressed that this is just a very simple approximation. The calculated factor is applied to the whole subhalo mass fraction as a correction to the normalization, without taking into account a possible dependence on subhalo mass. In particular, the situation with very low mass subhaloes 