They make switchable ballast yes. They also make conversion bulbs so you can run a MH light in a HPS ballast. As well as the other way around. They have been on the market for years, it's nothing new.
Zandor Reviewed by Zandor on . Mh conervsion bulb runnin on hps ballast so if im correct you can run a 400w mh conversion bulb on a 400w hps grow light system with a ballast??? this is what im thinkin about buying...will it work ok??? http://cgi.ebay.com/400W-HPS-MH-CONVERSION-Bat-Wing-Grow-Light_W0QQitemZ7755230101QQcategoryZ42225QQrdZ1QQcmdZViewItem Rating: 5