Information from: Organic Light-Emitting Diodes (OLEDs) Tutorial
[The old “ray-gun” approach of computer monitors:] Cathode Ray Tubes (CRTs) shoot electrons toward a phosphorescent screen. The electron beam leaves a bright spot wherever it strikes the phosphor screen.
[The newer flat screens and laptop screens:] Liquid Crystal Displays (LCDs) block or pass light reflected from an external light source or provided by a back lighting system. LCDs consist of liquid crystal electrodes sealed between two glass substrates.
[The future “rollup” screens:] An OLED is an electronic device made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted. These systems are usually less than 500 nm (0.5 thousandths of a millimeter). The displays have a wide viewing angle, and require very little power.