  The complex processes underlying the generation of a coherent-like emission
from the multiple-scattering of photons and wave-localization in the presence
of structural disorder are still mostly un-explored. Here we show that a single
nonlinear Schroedinger equation, playing the role of the Schawlow-Townes law
for standard lasers, quantitatively reproduces experimental results and
three-dimensional time-domain parallel simulations of a colloidal laser system.
