Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
Wet.
or
A porcupine with split ends
or
Ah-choo-choo!
or
He was tired of working for peanuts.
or
Microwaves.
or