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General characteristics Screen sizes have increased since the 21 inch display in 1992. The largest Plasma display in the world was shown at the CES (Consumer Electronics Show) in Las Vegas in 2006. It measured 103" and was made by Matsushita Electrical Industries (Panasonic). Twisted Nematic displays contain liquid crystal elements which twist and untwist at varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, the light is polarized to pass through the cell. In proportion to the voltage applied, the LC cells twist up to 90 degrees changing the polarization and blocking the light's path. By properly adjusting the level of the voltage most any grey level or transmission can be achieved. Brief history Quality control A plasma display is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. The gas discharge contains no mercury (contrary to the backlights of an AMLCD); a mixture of noble gases (neon and xenon) is used instead. This gas mixture is inert and entirely harmless.
Reflective LCDs, often found in digital watches and calculators, are illuminated by external light reflected by a (sometimes) diffusing reflector behind the display. This type of LCD can produce darker 'blacks' than the transmissive type since light must pass through the liquid crystal layer twice and thus is attenuated twice, however because the reflected light is also attenuated twice in the translucent parts of the display image contrast is usually poorer than a transmissive display. The absence of a lamp significantly reduces power consumption, allowing for longer battery life in battery-powered devices; small reflective LCDs consume so little power that they can rely on a photovoltaic cell, as often found in pocket calculators. In color LCDs each individual pixel is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters. Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel. Older CRT monitors employ a similar method for displaying color. Color components may be arrayed in various pixel geometries, depending on the monitor's usage. The glass panels seem to be vacuum sealed, because when they are broken,the plasma breaks up,seemingly from the addition of air to the space. Reflective LCDs, often found in digital watches and calculators, are illuminated by external light reflected by a (sometimes) diffusing reflector behind the display. This type of LCD can produce darker 'blacks' than the transmissive type since light must pass through the liquid crystal layer twice and thus is attenuated twice, however because the reflected light is also attenuated twice in the translucent parts of the display image contrast is usually poorer than a transmissive display. The absence of a lamp significantly reduces power consumption, allowing for longer battery life in battery-powered devices; small reflective LCDs consume so little power that they can rely on a photovoltaic cell, as often found in pocket calculators. Pioneering work on liquid crystals was undertaken in the late 1960s by the UK's Radar Research Establishment at Malvern. The team at RRE supported ongoing work by George Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals (which had all of the correct stability and temperature properties for application in LCDs). A diagram of the Pixel layout
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Normal Liquid Crystal Displays like those found in calculators have direct driven image elements – a voltage can be applied across one segment without interfering with other segments of the display. This is impractical for a large display with a large number of pixels since it would require millions of connections - top and bottom connections for each of red, green and blue of every pixel. To avoid this issue, the pixels are addressed in rows and columns which reduce the connection count from millions to thousands. If all the pixels in one row are driven with a positive voltage and all the pixels in one column are driven with a negative voltage, then the pixel at the intersection has the largest applied voltage and is switched. The problem with this solution is that all the pixels in the same column see a fraction of the applied voltage as do all the pixels in the same row, so although they are not switched completely, they do tend to darken. The solution to the problem is to supply each pixel with its own transistor switch which allows each pixel to be individually controlled. The low leakage current of the transistor also means that the voltage applied to the pixel does not leak away between refreshes to the display image. Each pixel is a small capacitor with a transparent ITO layer at the front, a transparent layer at the back and a layer of insulating liquid crystal between. History * Many users of older (around pre-2000) LCD monitors get migraines and other severe eyestrain problems from the flicker nature of the fluorescent backlights. If you experience eyestrain issues with LCDs, consider these possibilities: using a small resolution for reading text, on a >=15 inch LCD, glare from another light, brightness is set too low or high, defective backlight, LCD monitor is too close, or too far away, Not using WindowsXP Cleartype (generally helps improve font visibility, but can cause some problems in some cases).
Value TFT screens and most 38 cm (~15 in.) sized LCDs usually fail to include a digital signal compatible DVI interface, thus their future proofing may be limited. The upper end of 43 cm (~17 in.) or 48 cm (~19 in.) gamer and office TFT screens may have dual analog-VGA and DVI sockets; almost all professional screens have DVI and pivot mode for letter-mode display. However, the use of a DVI video signal does not automatically guarantee better image quality: a good video card RAMDAC and properly shielded analogue VGA cable may produce a better display than a bad video card and DVI. LCDs can be either transmissive or reflective, depending on the location of the light source. A transmissive LCD is illuminated from the back by a backlight and viewed from the opposite side (front). This type of LCD is used in applications requiring high luminance levels such as computer displays, televisions, personal digital assistants, and mobile phones. The illumination device used to illuminate the LCD in such a product usually consumes much more power than the LCD itself. Construction A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices. LCD technology still has a few drawbacks in comparison to some other display technologies: Main article: TFT LCD