A blackboard.
or
The letter G.
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
Shamboo!
Frankenstein: Witch can you make me a lemonade?
Witch: Poof you are a lemonade!
or
The letter H.
or
but I couldn't find any.
or
Does it have to be a light bulb? I've got this neat candle holder...
or