Lawsuits.
or
Two. One to take out the bulb and drop it, and the other to try and sell it before it crashes (knowing that it's already burned out).
or
50. One to screw in the light bulb and the remaining 49 to guard him .
or
6: 2 to screw in the bulb and 4 to testify that it was lit from the moment they began screwing.
or
Because sometimes you can get rid of cancer.
or
Because he wanted sweet dreams.
or