It is important to choose the correct ballast to match not only the type of grow light but also your pocketbook. You will need a separate ballast depending on whether you are using a Metal Halide or High Pressure Sodium bulb. Or you may get a convertible ballast that is able to switch between the two and all you need to do is change the bulb. HydroWarehouse is happy to offer you a great selection of ballasts for all of your hydroponic gardening needs.