We report on a transparent analysis of the luminescence spectra of dense electron-hole plasmas confined in GaAs/(Ga,Al)As quantum wells. We fit the spectra using the fact that the total number of particle states does not depend on collision broadening. Further, the effective dispersion of the valence and conduction subbands and the dependence of the optical matrix elements on wavevector is accounted for. We find (a) that the lowest subbands shift almost rigidly with changing plasma density, and (b) that the theoreticallly calculated band gap shrinkage (random phase approximation) is always higher than the experimental values.