There’s two ways of looking at this but I wouldn’t go to the barricades over either of them: this is either your light for your benefit and you have been allowed to place it on common property or it’s their light and you have sole use of it.
I reckon if push came to shove, the Owners Corp would have a very strong argument for saying this is your responsibility since it only benefits you and your guests.
On the other hand, if there’s a safety issue – the CP area under the light would be unsafe without it – , then they would probably have to provide a light in any case.
For the sake of good relations with your neighbours, I’d just buy the new light globe and ask them for help in replacing it if it’s not readily accessible.