The aim of this investigation is to show, whether totally different calibration methods (absolute spectral response at Fraunhofer ISE, blackbody at various temperatures at SERC) give similar results for the performance of TPV cells under infrared spectra. Two cell types (InGaAs and GaSb) have been tested, applying two different methods to each cell type. Spectral responses and I-V-curves of the cells have been measured. To compare the two methods the spectra of a halogen light bulb were measured up to 1.6 µm at different lamp currents and then fitted to the Planck formula and in this way extended into the infrared. The two methods are compared to each other and results are discussed. It is shown that the I-V-curves of both cell types are independent of the used spectrum. The currents of the cells measured at SERC and calculated at Fraunhofer ISE differ only in the range of measurement errors.