Liquid crystal display
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2008-07-16T21:31:53Z
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{{redirect|LCD}}
[[Image:LCD layers.svg|thumb|300px|Reflective twisted nematic [[liquid crystal]] display.
<ol><li>[[polarisation|Polarizing]] filter film with a vertical axis to polarize light as it enters. </li>
<li>Glass substrate with [[Indium tin oxide|ITO]] [[electrode]]s. The shapes of these electrodes will determine the dark shapes that will appear when the LCD is turned on or off. Vertical ridges etched on the surface are smooth.</li>
<li>Twisted nematic liquid crystals.</li>
<li>Glass substrate with common electrode film (ITO) with horizontal ridges to line up with the horizontal filter.</li>
<li>Polarizing filter film with a horizontal axis to block/pass light.</li>
<li>Reflective surface to send light back to viewer. (In a backlit LCD, this layer is replaced with a light source.)</li></ol>]]
A '''[[liquid crystal]] display''' ('''LCD''') is a thin, flat [[display device]] made up of any number of color or [[monochrome]] [[pixel]]s arrayed in front of a [[light source]] or [[reflector]]. It is often utilized in [[battery (electricity)|battery]]-powered [[electronics|electronic]] devices because it uses very small amounts of [[electric power]].
== Overview ==
[[Image:MA-2.JPG|right|thumb|250px|LCD alarm clock]]
Each [[pixel]] of an LCD typically consists of a layer of [[molecule]]s aligned between two [[transparency (optics)|transparent]] electrodes, and two [[polarization|polarizing]] [[filter (optics)|filter]]s, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no [[liquid crystal]] between the polarizing filters, [[light]] passing through the first filter would be blocked by the second (crossed) polarizer.
The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes
are made of a transparent conductor called [[Indium Tin Oxide]] (ITO).
Before applying an [[electric field]], the orientation of the liquid crystal molecules is determined by the alignment at the surfaces. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a [[helix|helical]] structure, or twist. Because the liquid crystal material is [[birefringence|birefringent]], light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the incident light is absorbed by the first polarizing filter, but otherwise the entire assembly is reasonably transparent.
[[Image:LCDpos.jpg|left|thumb|LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are crossed.]]
When a [[voltage]] is applied across the [[electrodes]], a [[torque]] acts to align the liquid crystal molecules [[parallel]] to the [[electric field]], distorting the helical structure (this is resisted by [[elastic forces]] since the molecules are [[constrained]] at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears [[gray]]. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the [[pixel]] will appear [[black]]. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.
[[Image:LCDneg.jpg|left|thumb|LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel.]]
The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device.
Both the liquid crystal material and the alignment layer material contain [[ionic compound]]s. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an [[alternating current]] or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).
When a large number of pixels are needed in a display, it is not technically possible to drive each directly since then each pixel would require independent electrodes. Instead, the display is ''[[multiplexer|multiplexed]]''. In a multiplexed display, electrodes on one side of the display are grouped and wired together (typically in columns), and each group gets its own [[voltage source]]. On the other side, the electrodes are also grouped (typically in rows), with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink.
==Specifications ==
Important factors to consider when evaluating an LCD monitor:
* [[Display resolution|Resolution]]: The horizontal and vertical size expressed in pixels (e.g., 1024x768). Unlike monochrome [[CRT monitors]], LCD monitors have a native-supported resolution for best display effect.
* [[Dot pitch]]: The distance between the centers of two adjacent pixels. The smaller the dot pitch size, the less granularity is present, resulting in a sharper image. Dot pitch may be the same both vertically and horizontally, or different (less common).
* Viewable size: The size of an LCD panel measured on the diagonal (more specifically known as active display area).
* [[Lcd Response Time|Response time]]: The minimum time necessary to change a pixel's color or brightness. Response time is also divided into rise and fall time. For LCD Monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult.
* [[Refresh rate]]: The number of times per second in which the monitor draws the data it is being given. A refresh rate that is too low can cause flickering and will be more noticeable on larger monitors. Many high-end LCD televisions now have a 120 Hz refresh rate (current and former [[NTSC]] countries only). This allows for less distortion when [[movie]]s filmed at 24 frames per second (fps) are viewed due to the elimination of [[telecine]] (3:2 pulldown). The rate of 120 was chosen as the [[least common multiple]] of 24 fps (cinema) and 30 fps (TV).
* [[#Passive-matrix and active-matrix addressed LCDs|Matrix type]]: Active or Passive.
* [[Viewing angle]]: (coll., more specifically known as [[:Image:Viewing-Direction-mB-June207.png|viewing direction]]).
* Color support: How many types of colors are supported (coll., more specifically known as color [[gamut]]).
* [[Brightness]]: The amount of light emitted from the display (coll., more specifically known as [[luminance]]).
* [[Contrast ratio]]: The ratio of the intensity of the brightest bright to the darkest dark.
* [[Aspect ratio]]: The ratio of the width to the height (for example, 4:3, 16:9 or 16:10).
* Input ports (e.g., [[Digital Visual Interface|DVI]], [[Video Graphics Array|VGA]], [[Low-voltage differential signaling|LVDS]], or even [[S-Video]] and [[High-Definition Multimedia Interface|HDMI]]).
== Brief history ==
* [[1888]]: [[Friedrich Reinitzer]] (1858-1927) discovers the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and generation of colors) and published his findings at a meeting of the Vienna Chemical Society on [[May 3]], [[1888]] (F. Reinitzer: ''Beiträge zur Kenntniss des Cholesterins, Monatshefte für Chemie (Wien) 9, 421-441 (1888)'').<ref>Tim Sluckin: ''Ueber die Natur der kristallinischen Flüssigkeiten und flüssigen Kristalle'' (''The early history of liquid crystals''), Bunsen-Magazin, 7.Jahrgang, 5/2005
</ref>
* [[1904]]: [[Otto Lehmann]] publishes his work ''"Liquid Crystals"''.
* [[1911]]: [[Charles Mauguin]] first experiments of liquids crystals confined between plates in thin layers.
* [[1922]]: [[George Friedel]] describes the structure and properties of liquid crystals and classified them in 3 types (nematics, smectics and cholesterics).
* [[1936]]: The [[Marconi Company|Marconi Wireless Telegraph company]] patents the first practical application of the technology, ''"The Liquid Crystal Light Valve"''.
* [[1962]]: The first major English language publication on the subject ''"Molecular Structure and Properties of Liquid Crystals"'', by Dr. [[George W. Gray]].<ref>George W. Gray, Stephen M. Kelly: ''"Liquid crystals for twisted nematic display devices"'', J. Mater. Chem., 1999, 9, 2037–2050</ref>
* [[1962]]: Richard Williams of RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what is now called “Williams domains” inside the liquid crystal.<ref>R. Williams, “Domains in liquid crystals,” J. Phys. Chem., vol. 39, pp. 382–388, July 1963</ref>
* [[1964]]: In the fall of 1964 [[George H. Heilmeier]], then working in the RCA laboratories on the effect discovered by Williams realized the switching of colors by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal. Practical problems with this new electro-optical effect made Heilmeier to continue work on scattering effects in liquid crystals and finally the realization of the first operational liquid crystal display based on what he called the ''dynamic scattering mode'' (DSM). Application of a voltage to a DSM display switches the initially clear transparent liquid crystal layer into a milky turbid state. DSM displays could be operated in transmissive and in reflective mode but they required a considerable current to flow for their operation.<ref name="cast06">{{Citation | title=Modifying Light | first1=Joseph A. | last1=Castellano | journal=American Scientist | volume=94 | issue=5 | year=2006 | pages=pp. 438-445}}</ref><ref>G. H. Heilmeier and L. A. Zanoni, “Guest-host interactions in nematic liquid crystals. A new electro-optic effect,” Appl. Phys. Lett., vol. 13, no. 3, pp. 91–92, 1968</ref><ref>G. H. Heilmeier, L. A. Zanoni, and L. A. Barton, “Dynamic scattering: A new electrooptic effect in certain classes of nematic liquid crystals,” Proc. IEEE, vol. 56, pp. 1162–1171, July 1968</ref>
* 1960s: Pioneering work on liquid crystals was undertaken in the late 1960s by the [[United Kingdom|UK]]'s [[Royal Radar Establishment]] at [[Great Malvern|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 correct stability and temperature properties for application in LCDs).
* [[1970]]: On December 4, 1970, the [[twisted nematic field effect]] in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, ([http://www.lcd-experts.net/ Swiss patent No. 532 261]) with Wolfgang Helfrich and [[Martin Schadt]] (then working for the Central Research Laboratories) listed as inventors.<ref name="cast06" /> Hoffmann-La Roche then licensed the invention to the Swiss manufacturer Brown, Boveri & Cie who produced displays for wrist watches during the 1970s and also to Japanese electronics industry which soon produced the first digital quartz wrist watches with TN-LCDs and numerous other products. [[James Fergason]] at the Westinghouse Research Laboratories in Pittsburgh while working with Sardari Arora and Alfred Saupe at [[Kent State University]] Liquid Crystal Institute filed an identical patent in the USA on April 22, 1971.<ref>{{cite web | title = Modifying Light | work = American Scientist Online | url = http://www.americanscientist.org/template/AssetDetail/assetid/53321/page/4;jsessionid=aaa6J-GFIciRx2%3Ci%3ELive }}</ref> In 1971 the company of Fergason [[ILIXCO]] (now [[LXD Incorporated]]) produced the first LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption.
* [[1972]]: The first active-matrix liquid crystal display panel was produced in the United States by T. Peter Brody.<ref>Brody, T.P., ''"Birth of the Active Matrix"'', Information Display, Vol. 13, No. 10, 1997, pp. 28-32.</ref>
* [[2007]]: In the 4Q of 2007 for the first time LCD surpassed CRT in worldwide sales.<ref>{{cite news |url=http://www.engadgethd.com/2008/02/19/worldwide-lcd-tv-shipments-surpass-crts-for-first-time-ever/ |title=Worldwide LCD TV shipments surpass CRTs for first time ever |publisher=engadgetHD |date=2008-02-19 |accessdate=2008-06-13}}</ref>
* [[2008]]: LCD TVs are the main stream with 50% market share of the 200 million TVs forecasted to ship globally in 2008 according to [[Display Bank]].<ref>{{cite news |url=http://www.displaybank.com/eng/info/news/press_show.php?id=2996 |title=Displaybank's Global TV Market Forecasts for 2008 - Global TV market to surpass 200 million units |publisher=Displaybank |date=2007-12-05 |accessdate=2008-06-13}}</ref>
A detailed description of the origins and the complex history of liquid crystal displays from the perspective of an insider during the early days has been published by Joseph A. Castellano in "Liquid Gold, The Story of Liquid Crystal Displays and the Creation of an Industry" <ref>LIQUID GOLD, The Story of Liquid Crystal Displays and the Creation of an Industry, 2005 World Scientific Publishing Co. Pte. Ltd., ISBN 981-238-956-3</ref>. Another book on the origins and history of LCD from a different perspective has been published by Hiroshi Kawamoto, available at the IEEE History Center.<ref>Hiroshi Kawamoto: [http://www.ieee.org/web/aboutus/history_center/lcd.html ''The History of Liquid-Crystal Displays''], ''Proc. IEEE'', Vol. 90, No. 4, April 2002</ref>
== Color displays ==
[[Image:LCD subpixel (en).png|thumb|left|300px|A subpixel of a color LCD]]
[[Image:Simulated LCD.png|thumb|Simulation of an LCD monitor up close]]
[[Image:XO screen 01 Pengo.jpg|thumb|Comparison of the [[OLPC XO-1]] display (left) with a typical color LCD. The images show 1×1 [[millimeter|mm]] of each screen. A typical LCD addresses groups of 3 locations as pixels. The XO-1 display addresses each location as a separate pixel.]]
In color LCDs each individual [[pixel]] is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters (pigment filters, dye filters and metal oxide filters). Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel. [[Cathode ray tube|CRT monitors]] employ a similar 'subpixel' structures ''via'' phosphors, although the electron beam employed in CRTs do not hit exact 'subpixels'.
Color components may be arrayed in various [[pixel geometry|pixel geometries]], depending on the monitor's usage. If software knows which type of geometry is being used in a given LCD, this can be used to increase the apparent resolution of the monitor through [[subpixel rendering]]. This technique is especially useful for text [[anti-aliasing]].
To reduce smudging in a moving picture when pixels do not respond quickly enough to color changes, so-called [[pixel overdrive]] may be used.
== Passive-matrix and active-matrix addressed LCDs==
[[Image:LCD display 16x2 alphanumeric.jpg|thumb|left|300px|A general purpose [[alphanumeric]] LCD, with two lines of 16 characters.]]
LCDs with a small number of segments, such as those used in [[digital watch]]es and [[pocket calculator]]s, have individual electrical contacts for each segment. An external dedicated [[Electronic circuit|circuit]] supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.
Small monochrome displays such as those found in personal organizers, or older [[laptop]] screens have a passive-matrix structure employing [[Super-twisted nematic display|super-twisted nematic]] (STN) or double-layer STN (DSTN) technology—the latter of which addresses a color-shifting problem with the former—and color-STN (CSTN)—wherein color is added by using an internal filter. Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called ''passive-matrix addressed'' because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow [[response time]]s and poor [[contrast]] are typical of passive-matrix addressed LCDs.
High-[[display resolution|resolution]] color displays such as modern LCD [[computer display|computer monitors]] and [[televisions]] use an [[Active-matrix liquid crystal display|active matrix]] structure. A matrix of [[thin-film transistor]]s (TFTs) is added to the polarizing and color filters. Each pixel has its own dedicated [[transistor]], allowing each column line to access one pixel. When a row line is activated, all of the column lines are connected to a row of pixels and the correct voltage is driven onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the row lines are activated in sequence during a [[Refresh rate|refresh]] operation. Active-matrix addressed displays look "brighter" and "sharper" than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images.
==Active matrix technologies==
[[Image:Casio LCD screen for digital camera.jpg|thumb|right|200px|A [[Casio]] 1.8" colour TFT liquid crystal display which equips the [[Sony]] Cyber-shot DSC-P93A [[digital camera|digital compact cameras]]]]
:''Main article:'' [[Thin film transistor liquid crystal display|TFT LCD]], [[Active-matrix liquid crystal display]]
===Twisted nematic (TN)===
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 almost any grey level or transmission can be achieved.
For a more comprehensive description refer to the section on the [[twisted nematic field effect]].
===In-plane switching (IPS)===
In-plane switching is an LCD technology which aligns the liquid crystal cells in a horizontal direction. In this method, the electrical field is applied through each end of the crystal, but this requires two transistors for each pixel instead of the single transistor needed for a standard thin-film transistor (TFT) display. This results in blocking more transmission area, thus requiring a brighter backlight, which will consume more power, making this type of display less desirable for notebook computers.
===Vertical alignment (VA)===
Vertical alignment displays are a form of LC displays in which the liquid crystal material naturally exists in a horizontal state removing the need for extra transistors (as in IPS). When no voltage is applied the liquid crystal cell, it remains perpendicular to the substrate creating a black display. When voltage is applied, the liquid crystal cells shift to a horizontal position, parallel to the substrate, allowing light to pass through and create a white display. VA liquid crystal displays provide some of the same advantages as IPS panels, particularly an improved viewing angle and improved black level.
===Blue Phase mode===
:''Main article:'' [[Blue Phase Mode LCD]]
In ''blue phase'' based LC-displays for TV applications it is not the selective reflection of light according the lattice pitch ([[Bragg]] reflection), but an electric field deforms the [[lattice]] which results in [[anisotropy]] of the refractive indices of the layer, followed by a change of [[transmission]] between crossed [[polarizer]]s.
Developed with a look at cost-efficiency, ''[[Blue Phase Mode LCD| blue phase mode LCD]]s'' do not require liquid crystal alignment layers, unlike today’s most widely used LCD modes such as [[Twisted nematic field effect|Twisted Nematic]] (TN), In-Plane Switching (IPS) or Vertical Alignment (VA) modes. The ''[[Blue Phase Mode LCD| blue phase mode]]'' can make its own alignment layers, eliminating the need for any mechanical alignment and rubbing processes. This reduces the number of required fabrication steps, resulting in savings on production costs. Additionally is has been claimed that blue phase panels will reduce sensitivity of the LC-layer to mechanical pressure which can impair the lateral uniformity of display luminance.
Overdrive circuits that are currently applied to many LCD panels with 120Hz [[frame]] [[frequency]] for improvement of the display of moving images in premium LCD TVs will become obsolete since the blue phase mode features a superior response speed, allowing images to be reproduced at 240Hz frame rate or higher without the need for any overdrive circuit <ref>Samsung Develops World’s First 'Blue Phase' Technology [http://www.physorg.com/news129997960.html], retrieved May 2008</ref>.
== Quality control ==
Some LCD panels have defective [[transistor]]s, causing permanently lit or unlit pixels which are commonly referred to as [[stuck pixel]]s or [[dead pixel]]s respectively. Unlike [[integrated circuits]] (ICs), LCD panels with a few defective pixels are usually still usable. It is also economically prohibitive to discard a panel with just a few defective pixels because LCD panels are much larger than ICs. Manufacturers have different standards for determining a maximum acceptable number of defective pixels. The maximum acceptable number of defective pixels for LCD varies greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea.<ref>{{cite web |title=Samsung to Offer 'Zero-PIXEL-DEFECT' Warranty for LCD Monitors |publisher=Forbes.com |date=December 30, 2004 |url=http://www.forbes.com/infoimaging/feeds/infoimaging/2004/12/30/infoimagingasiapulse_2004_12_30_ix_9333-0197-.html |accessdate=2007-09-03 }}</ref> Currently, though, Samsung adheres to the less restrictive [[ISO 13406-2]] standard.<ref>{{cite web |title=What is Samsung's Policy on dead pixels? |publisher=Samsung |date=February 5, 2005 |url=http://erms.samsungelectronics.com/customer/uk/jsp/faqs/faqs_view.jsp?SITE_ID=31&PG_ID=16&AT_ID=17628&PROD_SUB_ID=546 |accessdate=2007-08-03 }}</ref> Other companies have been known to tolerate as many as 11 dead pixels in their policies.<ref>{{cite web |title=Display (LCD) replacement for defective pixels - ThinkPad |publisher=Lenovo |date=June 25, 2007 |url=http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=MIGR-4U9P53 |accessdate=2007-07-13 }}</ref> Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the [[ISO 13406-2]] standard.<ref>{{cite web |url=http://www.jacobsen.no/anders/blog/archives/2006/01/04/what_is_the_iso_134062_standard_for_lcd_screen_pixel_faults.html |title=What is the ISO 13406-2 standard for LCD screen pixel faults? |publisher=Anders Jacobsen's blog |date=January 4, 2006}}</ref> However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways.
[[Image:lcd defects.png|thumb|right|300px|Examples of defects in LCDs]]
LCD panels are more likely to have defects than most ICs due to their larger size. In the example to the right, a 300 mm SVGA LCD has 8 defects and a 150 mm wafer has only 3 defects. However, 134 of the 137 dies on the wafer will be acceptable, whereas rejection of the LCD panel would be a 0% yield. The standard is much higher now due to fierce competition between manufacturers and improved quality control. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. Some manufacturers, notably in South Korea where some of the largest LCD panel manufacturers, such as LG, are located, now have "zero defective pixel guarantee", which is an extra screening process which can then determine "A" and "B" grade panels. Many manufacturers would replace a product even with one defective pixel. Even where such guarantees do not exist, the location of defective pixels is important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other. Manufacturers may also relax their replacement criteria when defective pixels are in the center of the viewing area.
LCD panels also have defects known as [[Mura (Japanese term)|''mura'']], which look like a small-scale crack with very small changes in [[luminance]] or [[color]].<ref>EBU – TECH 3320, ''"User requirements for Video Monitors in Television Production"'', EBU/UER, May 2007, p. 11.</ref> It is most visible in dark or black areas of displayed scenes. Defects in various LCD panel components can cause mura effect.{{clarifyme}}
== Zero-power (bistable) displays ==
The zenithal bistable device (ZBD), developed by [[QinetiQ]] (formerly [[Defence Evaluation and Research Agency|DERA]]), can retain an image without power. The crystals may exist in one of two stable orientations (Black and "White") and power is only required to change the image. [http://www.zbddisplays.com/ ZBD Displays] is a spin-off company from QinetiQ who manufacture both grayscale and color ZBD devices.
A French company, [http://www.nemoptic.com/ Nemoptic], has developed another zero-power, [[paper]]-like LCD technology which has been mass-produced since July 2003. This technology is intended for use in applications such as Electronic Shelf Labels, E-books, E-documents, E-newspapers, E-dictionaries, Industrial sensors, Ultra-Mobile PCs, etc. Zero-power LCDs are a category of [[electronic paper]].
Kent Displays has also developed a "no power" display that uses Polymer Stabilized Cholesteric Liquid Crystals (ChLCD). The major drawback to the ChLCD is slow refresh rate, especially with low temperatures.
In 2004 researchers at the [[University of Oxford]] demonstrated two new types of zero-power bistable LCDs based on Zenithal bistable techniques.<ref>{{cite web |title=Development of bistable displays |publisher=University of Oxford |author=Dr Chidi Uche |url=http://www.eng.ox.ac.uk/lc/research/Gratingstructures.html |accessdate=2007-07-13 }}</ref>
Several bistable technologies, like the 360° BTN and the bistable cholesteric, depend mainly on the bulk properties of the liquid crystal (LC) and use standard strong anchoring, with alignment films and LC mixtures similar to the traditional monostable materials. Other bistable technologies (i.e. Binem Technology) are based mainly on the surface properties and need specific weak anchoring materials.
==Drawbacks==
[[Image:ThinkPad Viewing Angle Comparison.JPG|250px|thumb|Two IBM [[ThinkPad]] laptop screens viewed at an extreme angle.]]
LCD technology still has a few drawbacks in comparison to some other display technologies:
*While CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCDs produce crisp images only in their "[[native resolution]]" and, sometimes, fractions of that native resolution. Attempting to run LCD panels at non-native resolutions usually results in the panel [[image scaling|scaling the image]], which introduces blurriness or "blockiness" and is susceptible in general to multiple kinds of [[HDTV blur]]. Many LCDs are incapable of displaying very low resolution screen modes (such as 320x200) due to these scaling limitations.
*Although LCDs typically have more vibrant images and better "real-world" contrast ratios (the ability to maintain contrast and variation of color in bright environments) than CRTs, they do have lower [[contrast ratio]]s than CRTs in terms of how deep their blacks are. A contrast ratio is the difference between a completely on (white) and off (black) pixel, and LCDs can have "backlight bleed" where light (usually seen around corners of the screen) leaks out and turns black into gray. However, as of December 2007, the very best LCDs can approach the contrast ratios of plasma displays in terms of delivering a deep black.
*LCDs typically have longer [[response time]]s than their plasma and CRT counterparts, especially older displays, creating visible [[ghosting]] when images rapidly change. For example, when moving the mouse quickly on an LCD, multiple cursors can sometimes be seen.
*Some LCD TVs have significant [[input lag]] due to slow video processing. If the lag delay is large enough, such displays can be unsuitable for fast and time-precise mouse operations ([[CAD]], [[first-person shooter|FPS]] gaming) as compared to CRT displays or other LCD panels with negligible amounts of input lag. Some LCD TVs have a "game mode" (the term used by Sony) that reduces both the amount of video processing and the amount of input lag.
*LCD panels using [[Thin film transistor liquid crystal display#Types|TN]] tend to have a limited [[viewing angle]] relative to CRT and plasma displays. This reduces the number of people able to conveniently view the same image – laptop screens are a prime example. Usually when looking below the screen, it gets much darker; looking from above makes it look lighter. Many panels which are based on the IPS, MVA, or PVA panels have much improved viewing angles; typically the color only gets a little brighter when viewing at extreme angles.
*Consumer LCD monitors tend to be more fragile than their CRT counterparts. The screen may be especially vulnerable due to the lack of a thick glass shield as in CRT monitors.
*[[Dead pixel]]s can occur when the screen is damaged or pressure is put upon the screen; few manufacturers replace screens with dead pixels for free.
*Horizontal and/or vertical banding is a problem in some LCD screens. This flaw occurs as part of the manufacturing process, and cannot be repaired (short of total replacement of the screen). Banding can vary substantially even among LCD screens of the same make and model. The degree is determined by the manufacturer's [[quality control]] procedures.
*The [[cold cathode]] fluorescent bulbs typically used for back-lights in LCDs contain mercury. LED backlit LCD displays are mercury-free.
== See also ==
===LCD technologies===
*[[List of LCD matrices]]
*[[Thin film transistor liquid crystal display|TFT LCD]]
*[[Transreflective liquid crystal display]] – adaptation to environment brightness
*[[Active-matrix liquid crystal display]] (AMLCD)
*[[Anisotropic Conductive Film]]
*[[Backlight]]
*[[HDTV Blur]]
===Other display technologies===
*[[Comparison of display technology]]
**[[Cathode ray tube]] (CRT)
**[[Digital Light Processing]] (DLP)
**[[Field emission display]] (FED)
**[[Light-emitting diode]] (LED)
**[[Liquid crystal on silicon]] (LCOS)
**[[Organic light-emitting diode]] (OLED)
**[[Plasma display|Plasma display panel]] (PDP)
**[[Surface-conduction electron-emitter display]] (SED)
**[[Vacuum fluorescent display]] (VFD)
===Display applications===
*[[Television]] and [[digital television]]
*[[Liquid crystal display television]] (LCD TV)
*[[LCD projector]]
*[[Computer monitor]]
===Manufacturers===
<div style="-moz-column-count:4; column-count:4;">
*[[Acer (company)]]
*[[Aoc]]
*[[AU Optronics]]
*[[Barco]]
*[[BenQ]]
*[[Casio]]
*[[Chi Mei|Chi Mei Optoelectronics]]
*[[CoolTouch Monitors]]
*[[Corning Inc.]]
*[[Dell]]
*[[Eizo]]
*[[Epson]]
*[[Fujitsu]]
*[[Hansol]]
*[[Hewlett-Packard|HP]]
*[[iiyama (company)|iiyama]]
*[[International Display Works]]
*[[JVC]]
*[[Kyocera]]
*[[Lenovo]]
*[[LG.Philips LCD]]
*[[LXD Incorporated]]
*[[Medion]]
*[[NEC Display Solutions]]
*[[Panasonic]] (Matsushita)
*[[Polaroid Corporation]]
*[[Polytronix Inc.]]
*[[Powerlight]]
*[[Samsung Electronics]]
*[[Sharp Corporation]]
*[[S-LCD]]
*[[Sony]]
*[[Toshiba]]
*[[Videocon]]
*[[Viewsonic]]
*[[Vizio]]
*[[Wintek]]
*[[Xerox]]
</div>
==References==
{{reflist}}
== External links - Tutorials ==
*
[http://lcdinterfacing.googlepages.com/colorlcd Color LCD Interfacing],LCD Interfacing with microcontroller
*
* [http://solutions.3m.com/wps/portal/3M/en_US/Vikuiti1/BrandProducts/secondary/optics101/ Animated tutorial of LCD technology by 3M]
{{commonscat|Liquid Crystal Displays}}
* [http://nobelprize.org/educational_games/physics/liquid_crystals/history/ History and Physical Properties of Liquid Crystals by Nobelprize.org]
* [http://www.iupac.org/publications/pac/2001/7305/7305x0845.html Definitions of basic terms relating to low-molar-mass and polymer liquid crystals (IUPAC Recommendations 2001)]
* [http://plc.cwru.edu/tutorial/enhanced/files/textbook.htm An intelligible introduction to liquid crystals] from Case Western Reserve University
* [http://bly.colorado.edu/lcphysics.html Liquid Crystal Physics tutorial] from the Liquid Crystals Group, University of Colorado
* [http://www.eng.ox.ac.uk/lc/introduction/intro_1.html Introduction to liquid crystals] from the Liquid Crystal Technology Group, Oxford University
* [http://www.elis.ugent.be/ELISgroups/lcd/lc/lc.php Liquid Crystals & Photonics Group - Ghent University (Belgium)], good tutorial
* [http://liqcryst.chemie.uni-hamburg.de/lcionline/ Liquid crystals] Liquid Crystals Interactive Online (not updated since 1999)
* [http://www.lci.kent.edu Liquid Crystal Institute] Kent State University
* [http://www.tandf.co.uk/journals/titles/02678292.asp Liquid Crystals] a journal by Taylor&Francis
* [http://www.tandf.co.uk/journals/titles/15421406.asp Molecular Crystals and Liquid Crystals] a journal by Taylor&Francis
* [http://www.acceleratedanalysis.com/LC_hotspotdetection_procedure.html Hot-spot detection techniques for ic's]
* [http://www.mc2.chalmers.se/mc2/pl/lc/engelska/frame.html What are liquid crystals?] from Chalmers University of Technology, Sweden
===General information===
*[http://www.maxi-pedia.com/TFT+LCD+display+monitor+panel What is TFT and how it works], TFT LCD guide for dummies.
*[http://www.auo.com/auoDEV/content/technology/technology_tftprocess_popup_en.htm How LCDs are made], an interactive demonstration from AUO (LCD manufacturer).
* [http://www.vega.org.uk/video/programme/25 Development of Liquid Crystal Displays: Interview with George Gray, Hull University, 2004] – Video by the Vega Science Trust.
*[http://www.maths.soton.ac.uk/staff/Sluckin/crystals_that_flow/homepage.htm History of Liquid Crystals] – Presentation and extracts from the book ''Crystals that Flow: Classic papers from the history of liquid crystals'' by its co-author Timothy J. Sluckin
* {{cite web
|url=http://www.xbitlabs.com/articles/other/display/lcd-parameters.html
|accessdate=2008-05-17
|title=Contemporary LCD Monitor Parameters: Objective and Subjective Analysis
|publisher=X-bit labs
|date=2007-01-23
|author=Oleg Artamonov}}
* [http://www.presentationtek.com/2006/09/21/3lcd-microdisplay-technology/ Overview of 3LCD technology], Presentation Technology
* [http://www.diamondhmi.co.uk/pages.cfm?ID=4&Sub=44 LCD Module technical resources and application notes], Diamond Electronics
* [http://www.techmind.org/lcd/phasexplan.html LCD Phase and Clock Adjustment], Techmind offers a free test screen to get a better LCD picture quality than the LCDs "auto-tune" function.
*[http://pcsupport.about.com/od/maintenance/ht/cleanflatscreen.htm How to clean your LCD screen] About.com: PC Support
*[http://www.tftcentral.co.uk TFT Central]LCD Monitor Reviews, Specs, Articles and News
*[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Interfacing-LCD.html Interfacing Alphanumeric LCD to Microcontroller]
{{Display Technology}}
[[Category:Display technology]]
[[Category:Liquid crystal displays| ]]
[[af:Vloeikristalskerm]]
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[[br:Skramm strinkennoù liñvel]]
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[[ca:Pantalla de cristall líquid]]
[[cs:Displej z tekutých krystalů]]
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[[de:Flüssigkristallbildschirm]]
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[[eo:Likvokristala ekrano]]
[[fr:Écran à cristaux liquides]]
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[[ko:액정 디스플레이]]
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[[vi:Màn hình tinh thể lỏng]]
[[tr:Sıvı kristal ekran]]
[[uk:Рідкокристалічний дисплей]]
[[ur:بلوری سیال تظاہرہ]]
[[zh:液晶显示器]]