a ballast is an electronic component in a lighting system that controls the amount of current in a circuit. Without it, a grow light would fail to work.Modern
digital ballasts limit current flow without wasting electricity also help to extend the lifespan of grow lights.
So Factors to Consider While Buying a Digital Ballast which is measured in Watts / Light output.
Another important factor in hydroponics is heating. A ballast that emits a lot of heat will affect the temperature of your growing environment. Some ballasts may include a fan for cooling, but these are known to have a high failure rate.
A good ballast should also switch off automatically in case of a short circuit.
i recommend digital ballast is best way to use with above advantages.