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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). General characteristics 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. 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. 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.
Each pixel consists of a column of liquid crystal molecules suspended between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. Without the liquid crystals between them, light passing through one would be blocked by the other. The liquid crystal twists the polarization of light entering one filter to allow it to pass through the other. Competing displays include the Cathode ray tube, OLED, AMLCD, DLP, SED-tv and field emission flat panel displays. The main advantage of plasma display technology is that a very wide screen can be produced using extremely thin materials. Since each pixel is lit individually, the image is very bright and looks good from almost every angle. Because many plasma displays still have a lower resolution the image quality is often not quite up to the standards of good LCD displays or cathode ray tube sets, but it certainly meets most people's expectations. Also, most cheaper consumer displays appear to have an insufficient color depth - a moving dithering pattern may be easily noticible for a discerning viewer over flat areas or smooth gradients; expensive high-res panels are much better at managing the problem. 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.
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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. (Patterned Vertical Alignment) is a more advanced version of MVA technology offered by Samsung. Developed independently, it suffers from the same problems as MVA, but boasts the best contrast ratios of any TFT technology. With prices starting around US$2,000 and going all the way up past US$20,000 (as of 2004), these sets did not sell as quickly as older technologies like CRT. But as prices fall and technology advances, they have started to seriously compete against the CRT sets. Some 42" sets fell below $1,500 at major retailers like Best Buy and Costco during the 2005 Christmas season, and many of the retailers reported that plasma TVs were among the hottest selling items for that season. 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. IPS has since been superseded by S-IPS (Super-IPS), which has all the benefits of IPS technology with the addition of improved pixel refresh timing. Though color reproduction approaches that of CRTs, the contrast ratio remains relatively weak. S-IPS technology only appears in larger displays aimed at professionals, though pricing has come down to the reach of the typical consumer.
1936: The Marconi Wireless Telegraph company patents the first practical application of the technology, "The Liquid Crystal Light valve". Color displays The molecules of the liquid crystal have electric charges on them. By applying small electrical charges to transparent electrodes over each pixel or subpixel, the molecules are twisted by electrostatic forces. This changes the twist of the light passing through the molecules, and allows varying degrees of light to pass (or not to pass) through the polarizing filters. * LCD screens occasionally suffer from image persistence, which is similar to screen burn on CRT displays.