Apparatus and a method for operating high intensity discharge (HID) lamps at a predetermined substantially constant luminous flux output. A power-time characteristic is developed using a test lamp of similar type and rating to the HID lamps. This characteristic defines the power required at different times, which may be regularly spaced intervals of for example 20 hours, during the operating life of the HID lamps to operate the lamps at the predetermined luminous flux output. The power time characteristic is then “played back” in real time via a microprocessor based master controller for the HID lamps. The communications to the HID lamps may be wireless or hard wired. The result is that the HID lamps are operated at substantially constant lumens resulting in significant energy savings and improved lamp performance.