I have a couple of 600 watt digital ballest that I purchased last summer from Htg. One of the ballest has been using the same bulb since January without any problems, no filckering or reduction in the amount of light emission. The other one blew a bulb out the first day it was in operation, which I had never seen a magnetic do in all my time of growing. Thought it must have been a bad bulb or the fact that it was a cheaper bulb I placed in the hood to check the operation of the system. I never knew that they had a history of blowing 600 watt bulbs. They seem to operate just fine with more expensive brand bulbs like Sunmaster. No problems with them so far as I can tell. I will tell you a digital ballest runs cooler than a magnetic one.