a question about metal halide bulbs

[cprowler]

What ballasts are you using?

I know you said that you changed the bulb to the other ballast. How long did you run them on each ballast?

Sounds exactly like what happens to core & coil ballasts when they go bad. If they are electronic then I would get new bulbs, if that doesn't work contact the (electronic) balasts manufacturer and they should be able to figure it out.