  (Summary) Making use of scaling relations between the central and the total
galaxy luminosity of a dark matter halo as a function of the halo mass, and the
scatter in these relations, we present an empirical model to describe the
luminosity function (LF) of galaxies. We extend this model to describe relative
statistics of early-type, or red, and late-type, or blue, galaxies, with the
fraction of early type galaxies at halo centers, relative to the total sample,
determined only by the halo mass and the same fraction in the case of
satellites is taken to be dependent on both the halo mass and the satellite
galaxy luminosity. This simple model describes the conditional luminosity
functions, LF of galaxies as a function of the halo mass, measured with the 2dF
galaxy group catalog from cluster to group mass scales. Using 2dF measurements,
we extract information related to conditional mass function for halos from
extreme voids to dense regions in terms of the galaxy overdensity. We also
calculate the probability distribution function of halo mass, as a function of
the galaxy overdensity, and use these probabilities to address preferred
environments of red and blue galaxies. Our model also allow us to make
predictions, for example, galaxy bias as a function of the galaxy type and
luminosity, the void mass function, and the average galaxy luminosity as a
function of the density environment.
