The paper presents and discuss a new technique for the evaluation of the absorption spectrum of a body, whose coefficients of global absorption are known for a restricted number of incident grey-body spectra comprised in a given range of temperatures (T1, T2). Indeed, although the absorption spectra reconstructed through the method proposed are not faithful reproductions of the original spectra, they nevertheless allow to achieve very well approximated results if employed for the estimation of the coefficient of global absorption of whichever incident grey-body radiation emitted by a source with a temperature within the same range (T1, T2), with clear advantages for radiating heat transfer computations. It is identified an optimum criteria to choose the radiating temperatures, which allows to bring down to 6 the number of sources needed to rebuild the spectrum. Finally, it is verified that a computed spectrum allows obtaining a well approximate results in the study of radiation heat transfer, even in case multiple reflections are not negligible.