Dead Ballast or burnt out bulb?

[JenniferL]

I have a 2x250W HQI metal halide light fixture. Noticed one of my bulbs not on today. This sounds like a stupid question but how do I know if its my bulb or ballast that has quite? I have only had this fixture for about 8 months. The ballast that runs that bulb is cold while the other one is warm, so does that mean that the ballast is not working?

[apexifd]

switch the ballast around. see if the other bulb lights up or not. or switch the bulbs around.

[Delphinus]

Yeah, pretty much you have to try a different lamp, at least you have two setup so swapping is easy and you don't have to worry about begging/borrowing/buying for a new lamp only to find out it wasn't the lamp. However fwiw, double-ended lamps are pretty delicate, it's my guess that it is the lamp and not the ballast (this has happened with me a few times too - the lamp just craps out after a while). The ballast is probably cool simply because the lamp is not lit.