How can you tell if a fluorescent light ballast is bad?

I know the obvious %26quot;change the bulb%26quot;. Does anyone know the acceptable output voltage ranges and how to check them safely? I have a lot of fixtures and when doing trouble shooting/maintenance, I always end up with bulbs and ballast of unknown condition.How can you tell if a fluorescent light ballast is bad?
I think the ballast rating is written on the thing itself. They all vary. I know that one is going bad when you notice a more frequent change of bulbs. Eventually a bad ballast will just burn out a brand new set of bulbs. why don't you write down the bulb change date and ballast change date on each fixture? Hope this helps.How can you tell if a fluorescent light ballast is bad?
Have a good look at it they usually show sign's of burning or over heating, if in doubt it's better to change them as they are not easy to check without the proper tools.