a ballast regulates the current to the lamps and provides sufficient voltage to start the lamps. Without a ballast to limit its current, a lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw. very quickly the lamp would overheat and burn out. During lamp starting, the ballast must briefly supply high voltage to establish an arc between the two lamp electrodes. Once the arc is established, the ballast quickly reduces the voltage and regulates the electric current to produce a steady light output. you will need a 400w ballast, there are 2 types, magnetic and digital. digitals are more expensive but run cooler and are more efficient with your electric,hence in the long run will save your hard earned cash. id go 4 a 400w dimable digital lumatek ballast if funds allow. however a magnetic ballast works just aswell and the heat output wouldnt be an issue if u mount the ballast outside ur grow space. cheapest place ive seen both the magnetic and the digital ballasts is ebay. u can get a magnetic 400w ballast for around £50 and a digital for around £100. hope this helps u mate. best wishes. peace.
