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Main article: TFT LCD A general purpose alphanumeric LCD, with two lines of 16 characters. Many LCDs are driven to darkness by an alternating current, which disrupts the twisting effect, and become faint or transparent when no current is applied.
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. The Plasma display panel was invented at the University of Illinois at Urbana-Champaign by Donald L. Bitzer and H. Gene Slottow in 1964 for the PLATO Computer System. The original monochrome (usually orange or green) panels enjoyed a surge of popularity in the early 1970s because the displays were rugged and needed neither memory nor refresh circuitry. There followed a long period of sales decline in the late 1970s as semiconductor memory made CRT displays incredibly cheap. Nonetheless, plasma's relatively large screen size and thin profile made the displays attractive for high-profile placement such as lobbies and stock exchanges. In 1983, IBM introduced a 19" orange on black monochrome display (model 3290 'information panel') which was able to show four simultaneous 3270 virtual machine (VM) terminal sessions. In 1992, Fujitsu introduced the world's first 21-inch full color display. It was a hybrid based on the plasma display created at the University of Illinois at Urbana-Champaign and NHK STRL, achieving superior brightness. General characteristics
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A Color LCD is a descendant of the primative monochrome LCD. This kind of LCD can emulate almost any real-life image compared to a monochrome LCD. Until quite recently (c. 2004) the superior brightness and viewing angle of color plasma panels, when compared to LCD, made them one of the most popular forms of display for HDTV. However since that time improvements in LCD technology have closed the gap dramatically. The much lower weight, price and power consumption of LCDs have seen them make large inroads into the former plasma market. Sony now only sell a very limited range of Plasma screens and appear set to quit this market altogether. Transflective LCDs work as either transmissive or reflective LCDs, depending on the ambient light. They work reflectively when external light levels are high, and transmissively in darker environments via a low-power backlight. Active matrix technologies 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.
1936: The Marconi Wireless Telegraph company patents the first practical application of the technology, "The Liquid Crystal Light valve". Raw LCD TFT panels are usually factory-sorted into three categories, with regard to the number of dead pixels, backlight evenness and general product quality. Additionally, there may be up to +/- 2ms maximum response time differences between individual panels that came off the same assembly line on the same day. The poorest-performing screens are then sold to no-name vendors or used in "value" TFT monitors (often marked with letter V behind the type number), the medium performers are incorporated in gamer-oriented or home office bound TFT displays (sometimes marked with the capital letter S), and the best screens are usually reserved for use in "professional" grade TFT monitors (usually marked with letter P or S after their type number). 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. 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. LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have a single electrical contact for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.