In order to estimate the performance of solar cells with downshifters under realistic irradiation conditions we used spectral distributions as they may be found outdoors. The spectral distributions were generated on a minutely basis by means of the spectrum simulation model SEDES2, using minutely measured data for global, direct, and diffuse irradiation from a Dutch meteorological station. Hourly aggregated spectra for a number of typical days (clear summer day, cloudy summer day, clear winter day, cloudy winter day) were used in modelling the output of the solar cell with and without downshifter. It was found that the simulated short current enhancement, which varies between about 7 and 23%, is linearly related with the average photon energy of the spectra. (c) 2007 Elsevier B.V. All rights reserved.