It doesn't matter, they don't have any electricity any more.
or
None. There never was any light bulb.
Notes: Probably the only really good light bulb joke of 1984.
or
In a hambulance.
or
Because each player raises a racquet.
or
They turn from notating nuclear spins to notating unclear puns.
or
Because 7 ate 9.
or
I've been framed!
or