Using a scanning tunneling microscope (STM), we have measured the microscopic surface roughness of light emitting tunnel junctions (LETJ) which consist of thin films of Al, Al oxide, and Au. The power spectrum of roughness obtained from the STM data was used to calculate the light emission spectrum, using a theory that takes into account the effect of surface roughness in first order perturbation. The calculated spectrum due to the term first order in roughness fits the measured emission spectrum very well, but when the term due to an unperturbed smooth surface is included, the fit becomes unsatisfactory. We conclude that the theory predicts a wrong ratio between the contribution from surface roughness and the contribution from a smooth surface.