Three - one to cast the bulb into the outer darkness, and two to catch it when it falls.
or
I was amazed, I never knew they worked.
or
He was tired of working for peanuts.
or
Climb up a tree and act like a nut
or
Dead.
or
None, because people who glow in the dark don't need light bulbs.
Note: Topical to the Chernobyl Reactor disaster of 1984.
or