The Cathode Ray Tube (CRT) is a vacuum tube which produces light when an electron beam hits its internal surface. An electron gun creates the electrons, and a high voltage source that accelerates them generates the electron beam.
The CRT is used as a picture displaying tube in video monitors, TV sets, computer monitors and others. The CRT uses an evacuated glass envelope which is large, deep, heavy, and relatively fragile. Display technologies without these disadvantages such as flat plasma displays, LCD, DLP, and OLED have replaced CRTs in many applications and are becoming increasingly common as costs decline.