The leaning tower of Pizza.
or
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
Only one, but they get three tech. reports out of it.
or
None. There never was any light bulb.
Notes: Probably the only really good light bulb joke of 1984.
or