A limited set of illuminants and phosphor colors are commonly used in video display terminal (VDT) working environments. This study attempts to identify any combinations of such conditions that influence performance on a visually demanding counting task. Experiments were performed to test whether the phosphor color, ambient lighting spectrum, or temporal frequency characteristics of the display and ambient lighting could alter performance. Under conditions where potentially contaminating variables such as reflectance level and screen glare patterns were equalized, no significant differences in performance were produced by the particular sets of stimulus conditions tested. The results suggest that displays and illuminant types that are in common use allow substantially equivalent visual performance.