Experimental VUV spectra from the JET tokamak and from the reversed field pinch RFX have been simulated. For the former device both n=2 to n=2 L-shell Ar and Ne spectra (respectively, in the 14.5–43.0 and in the 35.0-80.0nm ranges) were considered, whereas for RFX only the Ne spectrum was available. The spectra have been observed with the SPRED spectrometer. From the simulation of the spectra, relative sensitivity curves have been obtained for each instrument in the ranges of the simulation. For RFX only, it has been possible to extend this curve from ~13.0 to ~105nm, by simulating intrinsic C and O emissions. The photon emission coefficients of the lines with wavelengths in the ranges of the experimental spectra were obtained from collisional-radiative models. For Ar and Ne these coefficients have been calculated by the HULLAC atomic physics codes, whereas for C and O the corresponding coefficients have been taken from the ADAS database. Impurity modelling is performed using a one-dimensional impurity transport code, calculating for each atomic species the radial distribution of the impurity ions. The line brightnesses are evaluated in a post-processing subroutine and the simulations of the spectra are obtained. The spectral simulations (including impurity ion transport) give confidence in the atomic physics calculations, and allow the determination of the transport coefficients in the plasma regions from which the considered ionisation states emit. Finally, the obtained relative sensitivity curves of the two SPRED spectrometers have been compared with the calibrations performed by means of the branching ratio technique.