One; after reflecting in the twilight on the merit of the previous bulb.
or
Two, one to call Daddy, and one to get the (pick one:) mineral water/Tab.
or
They're both plastic and little boys turn them on.
or
He wanted to win the no-bell prize!
or
Do you want to grab a bite?
or
None, because people who glow in the dark don't need light bulbs.
Note: Topical to the Chernobyl Reactor disaster of 1984.
or
I got you covered.
or