I have several four foot fluorescent light fixtures in my basement. I recently found that some are marked that they take either T12 or T8 bulbs. Several others are not marked and currently have T12 bulbs.
Are these bulbs interchangable, or with T8 bulbs only go into specific fixtures?
I intend on opening up the fixtures to check the ballasts next time I'm up in the ceiling, but I'd like to know.