Only one. But he'll leave a big puddle of spit on the floor underneath him.
or
The baker, because he has lots of dough.
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or
Because they are black and white.
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Five: one to handle the bulb and four to contemplate how David Sanborn would've done it.
or