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
They don't lie.
or
It's not a shrub, it's a lemon tree my dear Watson.
or
I just found the Bush that Jeb lost."
or
None. The darkness will cause the bulb to change by itself.
or
A snail because it carries it's home.
or