The ballast is the power behind your hydroponic set up. If you want to get the most from your grow, and the most from your bulb, then don't skimp on quality. Getting the right ballast runs the bulbs at their correct settings and will provide full length of bulb life outputting the correct spectrum consistently. This ballast is robust and extremely reliable. High quality standards are never compromised HPS ? (High Pressure Sodium) This ballast is suited to run a HPS bulb and is most suitable for the bloom stage of growth. If you want a light for vegitive growth, you should select a MH (Metal Halide)