In areas you are walking under them 8ft clearance would be normal ceiling height. Above tables you can have them significantly lower. In olden dayz it was quite normal to have a 1ft cord from an 8ft ceiling but everyone walked about with their head lowered anyway because timez was sad.
How high does your ceiling need to be before you can use dangling lights? Are there rough guidelines?
I'd love to have some in my apartment, but I'm pretty sure I'd be walking into them all the time :(