There were two cows in a field. The first cow said "moo" and the second cow said "baaaa." The first cow asked the second cow, "why did you say baaaa?" The second cow said, "I'm learning a foreign language."
Depends. One, if it's an eco-kosher bulb that isn't going to be lit by electricity generated from nuclear power. Two, as long as a man and a woman rabbi have equal turns putting in the bulb. Three, one to change it, one to do a Buddhist mindfulness practice during the change, and one to document the paradigm shift in a best-selling book called The Jew in the Lightbulb. Four, same as above plus an additional rabbi to study the psycho-halachic implications of such a change and then lead a retreat weekend on the experience.