A 400 Volt HPS lamp is much more efficient than a standard HPS lamp. Both systems consume 1000 Watts and therefore cost exactly the same to run but the Pro HPS lamps run at a higher voltage and a lower current. 400 Volt Pro HPS lamps produce more light for the same power consumption and will give at least 10% higher yield compared to even the best standard HPS systems. In fact, when they are seen side-by-side, the HPS Pro lamps are noticeably brighter, run cooler and the light they produce is slightly whiter. So in addition to them giving a higher yield, plants grown under a 400 Volt Pro HPS are healthier, happier and are at less risk of heat damage too. The way that the system works is that UK mains power (230 Volts) is fed directly to the combined ballast and reflector via a standard mains power lead. The special ballast then converts the mains electricity to drive the special double ended 400 Volt / 1000 Watt EL lamp. The distance from the ballast to the lamp is very short, meaning that virtually no power is lost through the connecting cable. The reflector has been especially designed to give a superbly even light spread despite it's small size. The surface of the reflector has one of the best coatings available and gives at least 95% reflectivity. 400 Volt / 1000 Watt Pro HPS lamps maintain their efficiency and light output for much longer than standard HPS lamps. In fact they will normally last at least a year before they need to be changed out. It should be noted that normal HPS lamps and 400 Volt Pro HPS lamps are NOT interchangeable with different ballasts. Standard HPS lamps should only be used with standard or digital 230 Volt ballasts. 400 Volt Pro HPS lamps should only be used in lighting systems with a 400 Volt Pro HPS ballast like with this Gavita product. 400 Volt Pro HPS lamps can be identified by the HPS EL marking on them. The Gavita Pro 400 Volt / 1000 Watt HPS Lighting Kit includes a power control with 6 power settings so that it can be run at 600 Watts, 660 Watts, 750 Watts, 825 Watts, 1000 Watts or boosted to 1150 Watts! The fact that the Gavita Pro 400 Volt / 1000 Watt HPS light is dimmable and boostable makes the unit incredibly versatile.