Light bulb
From Memory Alpha, the free Star Trek reference
A light bulb is a device that runs an electrical current through it and produces light. Various types of light bulbs do this in different ways.
Vic Fontaine once referred to himself as a light bulb, acknowledging the fact that, as a hologram, he is little more than photons and force fields. Doctor Bashir's friends were surprised that Fontaine was a self-aware hologram, something they had never seen before. (DS9: "His Way")
