We have studied the electronic absorption spectra of niobium chloride and oxychloride compounds in different oxidation states and of the reduction products of pentavalent niobium and tantalum in various alkali chloride melts at different temperatures up to 1000 K. Furthermore, we present spectra of the corresponding cluster compounds Na4Nb6Cl18 and Na4Ta6Cl18 dissolved in alkali chloride melts at elevated temperatures. It is found that these compounds decompose at these temperatures. In comparing the spectra corresponding to the different oxidation states of the niobium systems, it is concluded that reduction of NbCl5 with excess metal yields Nb(II) or Nb(III), whereas in NbOCl3 the oxidation state IV is stabilized. These spectra are characterized by d-d and charge transfer bands. The optical absorption of TaCl5 reduced with excess metal exhibits the features typical of intervalence charge transfer : an intense asymmetric band at 1.6 eV whose intensity is reduced with temperature. The intensity of this band is correlated with an additional absorption visible in the infrared. These peculiarities of the electronic absorption are qualitatively discussed.