Two. One to screw it in, and one to stab the other in the back and take all the credit.
or
By carving a Trumpkin.
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None, because people who glow in the dark don't need light bulbs.
Note: Topical to the Chernobyl Reactor disaster of 1984.
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One's a spineless, poisonous blob. The other is a form of sea life.
or