None. The light bulb contains the seeds of its own revolution.
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
Stop! You're under a vest.
or
Five: one to handle the bulb and four to contemplate how David Sanborn would've done it.
or