Yes, you either need both an MH and an HPS ballast, or you get an HPS ballast and get a MH conversion bulb. Also, if your pockets are deep enough, you can get a switchable ballast, which allows you to exchange the sockets to be able to use both bulbs. The thing is, each bulb requires its own initial charge, provided by a transformer and capacitor circuit. The voltage is different for each bulb, so in that respect, they require different equipment, unless you get a conversion bulb. Got it?