Lightsaber

A fictional weapon of the Jedi Knights in the Star Wars universe. They are used like swords and can deflects bullets as well as cut through walls. The lightsaber of Jedi Knights fighting for peace and justice have a glowing blue or green colour, while the lightsaber of the Sith (Jedi Knights turned to the evil "dark side of power") have a glowing red colour.

When he tries to learn how to drive using a simulator, Sheldon wants his car to have the pale blue colour of Luke Skywalkers lightsaber (0205).

Leonard has a replica lightsaber that glows bluish-green. He used it to 'defend' himself when he thought there was an intruder in the apartment (0102).

NOTE: This visual gag was used in the original pilot, when Leonard came out after hearing a noise to discover that Katie had broken a lamp (0100).