Okay, it's a dual ballast that can fire EITHER type of bulb? This is like asking 'is it plugged in', but are you certain you toggled over to the HPS mode before switching bulbs? I've never used one of these but there should be a switch on it somewhere.
stinkyattic Reviewed by stinkyattic on . HPS/ballast issue. Having an issue with my HPS bulb. MH bulb works fine. Went to 12/12 and changed to the HPS bulb. Was working ok, then one morning when I went out to check on the grow it hadn't come on. Juice was getting to it since when I replaced it with the MH it went on immediately. Contacted the people I bought it from and they sent out a replacement bulb. Got the new HPS bulb, replaced it the next am and it lit up fine. Went out the next am, same thing not on and when replaced with MH works, fine. Rating: 5