Top panel: comparison of NESSY and ATLAS9 quiet Sun spectra to SIRS WHI observations Woods et al. (2009). NESSY spectra are calculated for three cases. Each case highlights the change in the spectrum at every single step in the progression from ATLAS9 LTE calculation with the set of U99 models to NESSY non-LTE calculation with the FAL99 models. The grey area designates the 1σ uncertainty range of the observations. NESSY and ATLAS9 spectra were convolved with the SIRS WHI spectral resolution. Bottom panel: comparison of facular, umbral and penumbral spectra. The colouring of the curves corresponds to that in the top panel. The three groups of curves on the main panel and the inset correspond, from bottom to top, to umbra, penumbra and facula. NESSY spectra are binned to the ATLAS9 spectral grid.