Visual Display Units
A computer monitor, or Visual Display Unit (VDU), is an output device that provides an interface for the user without leaving a permanent image. The monitor is compromised of a display device, the ability produce an image from the video signal sent by the source, and usually an enclosure. This signal contains a display adapter to generate video in a format compatible with the monitor. Usually, the signal is sent through a Visual Graphics Array (VGA), Digital Visual Interface (DVI), or High-Definition Multimedia Interface (HDMI) output port on the computer. The monitors come in many different forms. Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD) are the most popular displays at this time. Plasma Display Panel (PDP), Organic Light-Emitting Diode (OLED), and Surface-conduction Electron-emitter Display (SED) are other technologies that exist for producing a VDU. Cathode Ray Tubes refers to the tube that is inside of the monitor. An electron gun, in the tube, shoots electrons down the tube and onto a charged screen. The screen is coated with a pattern of phosphor dots that glow when struck by the electron stream. A pixel is one cluster of three dots: red, green and blue. The image displayed on the monitor consists of tens of thousands of pixels. The closer together the pixels are, the sharper the image on screen can be. The distance between pixels on a computer monitor screen is called dot pitch and is measured in millimeters. Most CRT monitors have a dot pitch of 0.28 mm or less. Though they have some advantages, such as a wide viewing angle, CRTs are becoming less prevalent as other technologies emerge. Their large size and weight, as well as higher power consumption, are contributing factors to the decline. A LCD is shaped into a thin, flat panel made up of pixels filled with liquid crystals and arrayed in front of a reflective mirror or source of light. An active-matrix of thin-film transistors (TFTs) is added to the polarizing and color filters. Each
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