Four. One to change it, one to sing about how heartbroken he is at the loss of the old one, one to sing about how madly in love he is with the new one, and one to go "Yee-Hah!" and throw his cowboy hat in the air.
You can throw away your light bulbs. Just douse the cat with gasoline, light it up with a match, and you'll have all the light you need. (Comment: BLEAH!)