Most instruments intended for luminescence spectroscopy fall in the category of uncorrected spectrofluorimeters. In many routine analyses, uncorrected spectra are useful, especially if they do not have to be compared with others from different laboratories. However, for theoretical work, results must be on an absolute basis. This paper describes a method and the related equipment that have been developed and used to obtain, on an absolute basis, many of the parameters that are important in photochemical research. The system can provide absolute emission spectra, absolute excitation spectra, and quantum efficiencies for luminescence, fluorescence, delayed fluorescence, and phosphorescence. Also, it can measure the half-life of phosphorescence and of delayed fluorescence. Provision is made for the independent and continuous control of the time between excitation and detection pulses, thus allowing the measurement of the half-life at any wavelength of emission. With these provisions it is possible to resolve overlapping fluorescence, delayed fluorescence, and phosphorescence spectra.