An embarrased mime!
or
Two… one to tell the engineer to do it, the other to say "I don't know, what do you think?"
or
None. There never was any light bulb.
Notes: Probably the only really good light bulb joke of 1984.
or
Twenty. One to hold the bulb, two to turn the ladder, and seventeen on the guest list.
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Anywhere it wants to
or