I am never sure. After I had turned on my actinics, I turned on my left mh (AB 10,000K w/ pulse start ballast) I then turned on the right mh (XM 10,000 w/ m58). The right one just started to fire up, then out. So I am like, what the? I fiddle around with this for about a half hour. I test the XM on the pulse start ballast (yeah, I know perhaps not the best idea). It fired up like a charm. so then I am like "well then its the ballast". that is when I posted on this board. I tried the XM on the m58 ballast and there was light. so now I am not really sure what the culprit is.