I have a 400w MH as well with a conversion bulb for flowering and can tell you that the HPS conversion bulb works well - it was about $130 though, so if you can't afford it then the MH should work too. Unfortunately I haven't tried using the regular MH bulb all the way through so I don't have anything to compare... at the end of the day though if you get the conversion bulb then you save those extra bulb hours by changing the bulb half way through your grow...
Dayzt1 Reviewed by Dayzt1 on . Metal Halide Hey all, im a noob, tho I have trolled for years and have half-assed tried to grow a few times with little avail. I seem to have a nice bagseed plant that is likely to show sex soon, my main question is: I am using a 400 watt metal halide (which kills the rinky-dink cfl's I had)... What will be the difference, when flowering, when compared to an HPS of the same wattage? I dont have a switchable ballast, so its not an option... tho I have seen some conversion bulbs, are they worthwhile? Rating: 5