We investigate the spectral broadening in deep ultraviolet (UV) multi quantum well light emitting diodes (LED) by modeling the emission spectra. Experimental emission spectra of deep UV LEDs exhibit a at tail towards lower energies and a steep decrease towards high energies that cannot be explained by convolution of the spectrum with a broadening function. We devise a luminescence model based on the broadening of the density of states (DOS) function which is consistent with the experimental spectra. The broadening of the DOS also explains the emission red shift with respect to the quantum well subband transitions. In addition, we investigate the in uence of the DOS broadening on the carrier and luminescence in the active region.