Flat-panel display device

Flat-panel display device

An electronic display in which a large orthogonal array of display elements, such as liquid-crystal or electroluminescent elements, form a flat screen. The term “flat-panel display” is actually a misnomer, since thinness is the distinguishing characteristic. Most television sets and computer monitors currently employ cathode-ray tubes. Cathode-ray tubes cannot be thin because the light is generated by the process of cathodoluminescence whereby a high-energy electron beam is scanned across a screen covered with an inorganic phosphor. The cathode-ray tube must have moderate depth to allow the electron beam to be magnetically or electrostatically scanned across the entire screen. See Cathode-ray tube

For a flat-panel display technology to be successful, it must at least match the basic performance of a cathode-ray tube by having (1) full color, (2) full gray scale, (3) high efficiency and brightness, (4) the ability to display full-motion video, (5) wide viewing angle, and (6) wide range of operating conditions. Flat-panel displays should also provide the following benefits: (1) thinness and light weight, (2) good linearity, (3) insensitivity to magnetic fields, and (4) no x-ray generation. These four attributes are not possible in a cathode-ray tube.

Flat-panel displays can be divided into three types: transmissive, emissive, and reflective. A transmissive display has a backlight, with the image being formed by a spatial light modulator. A transmissive display is typically low in power efficiency; the user sees only a small fraction of the light from the backlight. An emissive display generates light only at pixels that are turned on. Emissive displays should be more efficient than transmissive displays, but due to low efficiency in the light generation process most emissive and transmissive flat panel displays have comparable efficiency. Reflective displays, which reflect ambient light, are most efficient. They are particularly good where ambient light is very bright, such as direct sunlight. They do not work well in low-light environments.

Most flat-panel displays are addressed as an X-Y matrix, the intersection of the row and column defining an individual pixel (see illustration). Matrix addressing provides the potential for an all-digital display. Currently available flat-panel display devices range from 1.25-cm (0.5-in.) diagonal displays used in head-mounted systems to 125-cm (50-in.) diagonal plasma displays.

Currently, most commercially manufactured flat-panel display devices are liquid-crystal displays (LCDs). The benchmark for flat-panel display performance is the active matrix liquid-crystal display (AMLCD). Most portable computers use AMLCDs. Competing flat-panel display technologies include electroluminescent displays, plasma display panels, vacuum fluorescent displays, and field-emission displays. Electroluminescent displays are often used in industrial and medical applications because of their ruggedness and wide range of operating temperatures. Plasma display panels are most often seen as large flat televisions, while vacuum fluorescent displays are used in applications where the information content is fairly low, such as the displays on appliances or in automobiles. Field-emission displays are the most recent of these flat-panel technologies.

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