I had an 400 watt MH bulb on my last crop...The bulb would light up for about 5 minutes, or less and go out...It would come back on after awhile, but kept on turning off after a short time..I replaced the bulb with a new one, same problem...When I use an HPS bulb, it works fine...Should I replace the MH bulb again???Or is there something i'm doin' wrong???