I have a 400 watt hps ballast that ive been using a 400 watt mh light in for the last month and everything is still working. No bad bulb, no fires. The best thing to do would be buy a conversion bulb like others have said but depending on your ballast a mh bulb should work.
Also i dont recommend switching your bulbs out just so you get both light spectrums. That would be way too many bulb changes. IF you really feel like you need both spectrum just get a bulb that has both. The reason i say this is because in my setup i have 3 lights. 2 hps and 1 mh. I shit you not the plants under the mh look almost identical to the plants under the hps, and the plants that are getting both spectrum dont look any better than the plants that are only getting one. No matter what light you use, your going to get great buds as long as you know what you are doing and take good care of them. I say save your money and just keep using what you are using.
