In this Letter the results of applicability of Kirchhoff 's law as given by Salisbury and coworkers are discussed. In their paper, experimental evidence on the violation of Kirchhoff 's law for heterogeneous temperature regimes was given. In this Letter the hypothesis of the existence of a single 'sample temperature' resulting in measured emissivities which were less than the true values was demonstrated. Thus, the 'evidence' given by Salisbury and coworkers needs reviewing.