Liquid-crystal display
In 1888, Friedrich Reinitzer observed a strange behavior in cholesterol extracted from carrots. He found the substance melted twice and generated colors during the process. This discovery marked the first identification of liquid crystals by physicists like Otto Lehmann and Georges Friedel. Lehmann published his work "Flüssige Kristalle" (Liquid Crystals) in 1904 to describe these unique materials. Friedel later classified them into three types: nematics, smectics, and cholesterics. Vsevolod Frederiks devised an electrically switched light valve called the Fréedericksz transition in 1927. This effect became essential for all future LCD technology. The Marconi Wireless Telegraph company patented the first practical application known as "The Liquid Crystal Light Valve" in 1936. Richard Williams of RCA discovered electro-optic characteristics in 1962. He generated stripe patterns inside a thin layer of liquid crystal material by applying voltage. These patterns are now called Williams domains.
George H. Heilmeier achieved the switching of colors by field-induced realignment of dichroic dyes at RCA laboratories in 1964. He created the first operational liquid-crystal display based on dynamic scattering mode or DSM. Application of voltage switched the clear transparent liquid crystal layer into a milky turbid state. Hoffmann-LaRoche filed a patent for twisted nematic field effect on the 4th of December 1970. Wolfgang Helfrich and Martin Schadt were listed as inventors for Swiss patent No. 532 261. James Fergason filed an identical patent in the United States on the 22nd of April 1971. ILIXCO produced LCDs based on the TN-effect in 1971 which superseded poor-quality DSM types. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971 for an electronic wristwatch incorporating a TN-LCD. The Gruen Teletime became the first wristwatch with TN-LCD launched on the market in 1972. T. Peter Brody's team at Westinghouse demonstrated the first thin-film-transistor liquid-crystal display in 1973. Brody coined the term active matrix in 1975 after demonstrating the first flat active-matrix thin-film transistor liquid-crystal display.
Brown Boveri & Cie Research Center invented the super-twisted nematic structure for passive matrix-addressed LCDs in 1983. H. Amstutz et al. filed corresponding patent applications in Switzerland on the 7th of July 1983. Philips acquired Videlec AG company based in Switzerland in 1985 and moved production lines to the Netherlands. Sharp Corporation introduced dot matrix TN-LCD in 1983. Citizen Watch introduced the Citizen Pocket TV in 1984 as a 2.7-inch color LCD TV with the first commercial TFT LCD. In 1988, Sharp demonstrated a 14-inch active-matrix full-color full-motion TFT-LCD. This led Japan to launch an LCD industry developing large-size LCDs including computer monitors and televisions. The LCD industry began shifting away from Japan towards South Korea and Taiwan in the late 1990s. From 2001 to 2006, Samsung and five other major companies held 53 meetings in Taiwan and South Korea to fix prices. These six companies were fined 1.3 billion dollars by the United States. China became the largest manufacturer of LCDs in the 2020s with Chinese firms holding a 40% share of the global market. Local governments played a significant role through state-owned investment companies.
LCDs do not produce light on their own so they require external light to produce a visible image. Active-matrix LCDs are almost always backlit while passive LCDs may be reflective using ambient light. White LED arrays place LEDs behind a diffuser behind the panel for transmissive type displays. Cold cathode fluorescent lamps or CCFLs lit panels either by two lamps placed at opposite edges or parallel arrays behind larger displays. Edge-lit WLED technology places white LEDs at one or more edges of the screen. A light guide plate spreads the light evenly across the whole display. Quantum dots receive blue light from a backlight and convert it to light allowing better color reproduction. Mini-LED backlighting supports over a thousand Full-area Local Area Dimming zones. This allows deeper blacks and higher contrast ratio. Dynamic backlight control invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan increases dynamic range. The combination of reflective polarizers and LED dynamic backlight control makes today's LCD televisions far more efficient than CRT-based sets leading to worldwide energy saving of 600 TWh in 2017.
Passive-matrix LCDs were standard in most early laptops until the mid-1990s when color active-matrix became standard. Displays having a passive-matrix structure use super-twisted nematic STN technology invented by Brown Boveri Research Center in 1983. Individual pixels are addressed by corresponding row and column circuits without steady electrical charge. Active-matrix structures add a matrix of thin-film transistors to electrodes in contact with the LC layer. Each pixel has its own dedicated transistor allowing each column line to access one pixel. Twisted nematic displays contain liquid crystals that twist and untwist at varying degrees to allow light to pass through. In-plane switching aligns liquid crystals in a plane parallel to glass substrates requiring two transistors for each pixel instead of single transistor needed for standard TFT display. Vertical alignment displays form LCDs where liquid crystals naturally align vertically to glass substrates creating black display between crossed polarizers. Blue phase mode LCDs have been shown as engineering samples early in 2008 but not yet in mass production.
Resolution is expressed by number of columns and rows of pixels such as 1024x768. Each pixel usually composed of three sub-pixels red green and blue. Spatial performance varies per application with televisions generally having low density for long-distance viewing. Temporal resolution describes how well display can show changing images or accuracy times per second drawing data. Individual pixel response time important as all displays have inherent latency creating visual artifacts if image changes rapidly. Contrast ratio is ratio of brightness full-on pixel to full-off pixel. Black levels may not be dark enough because individual liquid crystals cannot completely block backlight from passing through. Display motion blur on moving objects caused by slow response times greater than 8 milliseconds. Dead or stuck pixels occur during manufacturing or after period of use. A stuck pixel glows with color even on all-black screen while dead one always remains black. Samsung held zero-tolerance policy for LCD monitors sold in Korea at one point. Other companies known to tolerate as many as 11 dead pixels in their policies. Clouding dirty screen effect involves uneven patches of luminance most visible in dark areas. ISO released standard ISO 9241-302 in 2008 regulating acceptability of defects.
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Common questions
Who discovered liquid crystals in 1888?
Friedrich Reinitzer observed the strange behavior of cholesterol extracted from carrots in 1888. This discovery marked the first identification of liquid crystals by physicists like Otto Lehmann and Georges Friedel.
When was the twisted nematic field effect patented?
Hoffmann-LaRoche filed a patent for the twisted nematic field effect on the 4th of December 1970. James Fergason filed an identical patent in the United States on the 22nd of April 1971.
Which company launched the first wristwatch with TN-LCD in 1972?
The Gruen Teletime became the first wristwatch with TN-LCD launched on the market in 1972. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971 for an electronic wristwatch incorporating a TN-LCD.
How much were six companies fined for fixing LCD prices between 2001 and 2006?
Samsung and five other major companies held 53 meetings in Taiwan and South Korea to fix prices from 2001 to 2006. These six companies were fined 1.3 billion dollars by the United States.
What is the difference between active-matrix and passive-matrix LCDs?
Passive-matrix LCDs address individual pixels using corresponding row and column circuits without steady electrical charge. Active-matrix structures add a matrix of thin-film transistors so each pixel has its own dedicated transistor allowing each column line to access one pixel.