Can a landlord charge you to replace light bulbs in a rental in Pennsylvania?

While that's kind of a crappy thing for him to do, that really could go either way. If light bulbs were provided when you moved in, and the lease specifies that you are responsible for replacing them, then yes, he can probably do that. But he can only deduct the actual cost of the light bulbs, so if this is more than a few bucks, he's probably in the wrong. One could make an argument that this is "normal wear and tear" which is not supposed to be deducted from security deposits, but now we're talking about fighting over a very small amount of money. It would probably cost you more than you'd recover if you took the landlord to court, assuming you even win. This is the kind of thing that you probably want to let go. It's not worth the trouble. But if your landlord is deducting more than the cost of the light bulbs from the deposit, there may be a more significant problem. If that's the case, consult a local landlord/tenant attorney.