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.
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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