  We derive and interpret some relations between the luminosity, mass, and age
distributions of star clusters, denoted here by phi(L), psi(M), and chi(tau),
respectively. Of these, phi(L) is the easiest to determine observationally,
whereas psi(M) and chi(tau) are more informative about formation and disruption
processes. For populations of young clusters, with a relatively wide range of
ages, phi(L) depends on both psi(M) and chi(tau) and thus cannot serve as a
proxy for psi(M) in general. We demonstrate this explicitly by four
illustrative examples with specific forms for either psi(M) or chi(tau). In the
special case in which psi(M) is a power law and is independent of chi(tau),
however, phi(L) is also a power law with the same exponent as psi(M). We
conclude that this accounts for the observed similarity between phi(L) and
psi(M) for the young clusters in the Antennae galaxies. This result reinforces
our picture in which clusters form with psi(M) propto M^{-2} and are then
disrupted rapidly at a rate roughly independent of their masses. The most
likely disruptive process in this first stage is the removal of interstellar
matter by the energy and momentum input from young stars (by photoionization,
winds, jets, and supernovae). The few clusters that avoid this "infant
mortality" are eventually disrupted in a second stage by the evaporation of
stars driven by two-body relaxation, a process with a strong dependence on
mass. We suspect this picture may apply to many, if not all, populations of
star clusters, but this needs to be verified observationally by determinations
of psi(M) and chi(tau) in more galaxies.
