I have used mh bulbs for years for blooming and like the results. imp: :dance:
A automated system and, have tested both hp and mh bulbs for blooming.
I like the mh due to less streach and tighter buds.
Note would buy 2 and have a spare, I like GE bulbs with the normal ballast.
Note mh are directional mount and U mount is universal. I realy think theres not much differance between bulb makers , just the box and the snow job of selling.
note 400 watts, not 4,000 and 4,000k would be one hell of a size bulb, like 4,000,000