Only photometers scanning a large range of wavelengths provide the amount of information which is necessary to analyze multicomponent systems in a general form. After a description of a rapid scanning photometer and a discussion of the recording problems, the mathematical method is described which allows an optimal analysis of the concentrations of the single components of a multicomponent system. The error involved in this procedure is demonstrated by the calculation of the four nucleotides in a mixture. The long range photometry has been successfully applied to other problems such as measurements by reflected light and analyses of inhomogeneously distributed substances in living tissues.