A whole synod. One to move that the bulb be changed while the others debate until the room spins.
or
Slippers.
or
Only two, but the hard part is getting them into the light bulb.
or
They screw millions of bulbs every day, but when it comes to your bulbs, there's no record.
or
1,622. One to tell the original joke, and the rest to submit give some minor variation of it! For example:
or