Marc raises a good point: it's very easy for someone to put the wrong bulb in these fixtures.
The result? damaged fixtures.
DON'T assume the right bulb is in the fixture. LOOK at the ballast and the fixyure; both should be identified as to what goes in.
OK, they make it confusing. Rather than say "250w MH", they say something like "M58." Still, you ought to be able to find a cross-reference ... for example, google "M58" and you'll find a description.
