In the study of photoluminescence, simple spectra obtained by dc excitation often do not contain sufficient information for complete analysis of the kinetics of the luminescent light emission. This paper describes a system with which the spectral emission can be studied at controlled times after photoexcitation. The system uses separate mechanical chopping of the photoexcitation source and the photoluminescent emission. The two light choppers are hysteresis synchronously driven from a single alternating current source and their relative positions are, therefore, phase locked. Their relative positions and, therefore, the time between termination of photoexcitation and detection of photoluminescent emission is controlled by a 0–360° precision electrical phase shifter placed between the common alternating current source and the power amplifier driving one of the chopper motors. This time controlled system is described. The photoluminescence is wavelength resolved by a spectrometer, detected by a photomultiplier and lock‐in amplifier, and automatically recorded as a function of wavelength by an X‐Y recorder. X‐Y recorded tracings of photoluminescent spectra at various times after termination of photoexcitation are shown to illustrate the capabilities of the system.