VIVOSUN Ultra Bright 400 Watt Digital Dimmable Electronic Ballast with Soft Start Technology and Built-in Fan for Hydroponic HPS MH Sodium Halide Grow Lamp Bulb Light (ETL Listed, USA Brand) Note:Ballast should be the same watts as the bulb, or it may blow your bulbs. The extra setting is to adjust the brightness of the bulb( lumen). Different lumens have different effect on the plants. Exclusive Technology: "Soft Start"-allows multiple ballasts to start at the same time."Slow Light Start-up"- a healthy way to starup the bulb and reduces risks of premature failure of bulbs. Strike both metal halide and high pressure sodium bulbs, compatible with Double Ended lamps. Can withstand a wide range of voltage fluctuations from 98V to 268V and still supply a constant voltage to the lamps What You Get: VIVOSUN ultra bright 1000w digital ballast, 8ft 120 Volt Power Cord, four Rubber feet, ETL certified guarantee, our fan-favorite 3-year warranty and friendly customer service.