LED & LCD & CRT

A liquid crystal display (LCD) is a flat panel display, electronic visual display, video display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly.

A light-emitting diode (LED) is a semiconductor light source.[1] LEDs are used as indicator lamps in many devices and are increasingly used for other lighting

The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen.