A lighting control system interfaced with the inexpensive VIC‐20 microcomputer is described which can automatically vary light intensity and photoperiod in the laboratory to simulate natural intensity curves throughout the day, and daylengths throughout the changing seasons. Adjustments to compensate for differing latitudes and habitat types are easily accomplished through modifications of the controlling software. The system enables the study of effects of crepuscular lighting and circannual periodicities of physiology and behavior which were previously infeasible. Circuit diagrams, details of construction for simultaneous control of three sets of lights, and a menu‐driven BASIC program for accurately simulating the annual light cycle for any point between the equator and 60 degrees north latitude are presented. The importance of photoenvironment in laboratory studies of physiology and behavior is discussed.