The letter H.
or
Does it have to be a light bulb? I've got this neat candle holder...
or
I said, "I can't make Tuesdays"
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Anything you like, he can't hear you.
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Five. Four to decide which way the bulb ought to turn, and . . .
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
In a hambulance.
or