Quote Originally Posted by JackHerer
If you don't already own the MH ballast system then whats the pont in fighting the flow of electricity to just be different you might as well get the most common system & benefit from the reduced purchase costs.
I was under the assumption, from the way the initial question was asked, that the poster was already using a MH system and wanted to know what would be more appropriate for flowering. In which case, barring any physical complications with the reflector, a conversion HPS would be feasible and economical. (Much better to save money and buy a conversion bulb than it is to buy an entirely new lighting system, right?) If you have an air-cooled & enclosed hood, I guess I could see a potential space issue...but there probably wouldn't be much interference in a light with an open hood.

If you have the money to get a switchable system, then by all means, get it. But if you happen to have an HPS-only, or a MH-only system, then conversion bulbs are the way to go if you want to veg under MH, and flower under HPS.