None. That's a software problem.
or
Does it have to be a light bulb? I've got this neat candle holder...
or
A hush puppy.
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It has a collar I.D.
or
None; the Bible doesn't mention any light bulbs.
or
Because the chicken was on vacation.
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Because he wears a size "S".
or
Five. One to tell the joke and one to get it.
or
None. They just steal somebody else's light.
or
No way Hose A.
or