Q: How many members of the U.S.S. Enterprise does it take to change a light bulb?
A: Seven. Scotty has to report to Captain Kirk that the light bulb in the Engineering Section is getting dim, at which point Kirk will send Bones to pronounce the bulb dead (although he'll immediately claim that he's a doctor, not an electrician).
Scotty, after checking around, realizes that they have no more new light bulbs, and complains that he "canna" see in the dark. Kirk will make an emergency stop at the next uncharted planet, Alpha Regula IV, to procure a light bulb from the natives, who, are friendly, but seem to be hiding something.
Kirk, Spock, Bones, Yeoman Rand and two red shirt security officers beam down to the planet, where the two security officers are promply killed by the natives, and the rest of the landing party is captured.
As something begins to develop between the Captain and Yeoman Rand, Scotty, back in orbit, is attacked by a Klingon destroyer and must warp out of orbit. Although badly outgunned, he cripples the Klingon and races back to the planet in order to rescue Kirk et. al. who have just saved the natives' from an awful fate and, as a reward, been given all light bulbs they can carry.
The new bulb is then inserted and the Enterprise continues on its five year mission.