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.
Six: two to screw in the bulb and four to testify that it was lit from the moment they began screwing.
None; the bulb will change itself when it is ready.