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28 février 2011 1 28 /02 /février /2011 03:55

A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly  (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

They are used in a wide range of applications, including computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones  Dell Studio XPS 1640 Battery .

LCDs have displaced cathode ray tube (CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in Dell Vostro 1710 Battery .

LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-poweredelectronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of alight source (backlight) or reflector to produce images in colour or monochrome Dell KM958 battery .

The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from 1888. By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units  Dell Studio 1555 battery .

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other  Sony VGP-BPS13 battery .

With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. In most of the cases the liquid crystal has double refraction  Sony VGP-BPS13/B battery .

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  Sony VGP-BPS13/S battery .

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 of electrodes  Sony VGP-BPS13A/B battery .

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 helical structure, or twist. This reduces the rotation of the polarization of the incident light, and the device appears grey  Sony VGP-BPS13B/B battery .

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  Sony VGP-BPL9 battery .

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. This electric field also controls (reduces) the double refraction properties of the liquid crystal  Sony VGP-BPS13B/B battery .

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) Sony VGP-BPL15 battery .

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 Dell Inspiron E1505 battery .

Both the liquid crystal material and the alignment layer material contain ionic compounds. 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 Dell Latitude E6400 battery .

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) HP Pavilion dv6000 Battery .

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 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  SONY VAIO VGN-FZ Battery .

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   SONY VAIO VGN-FZ18 Battery .

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 colours)  SONY VAIO VGN-FZ21E Battery
  • 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)).
  • 1911: Charles Mauguin first experiments of liquids crystals confined between plates in thin layers.
  • 1936: The 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  SONY VAIO VGN-FW21E Battery .
  • 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  SONY VAIO VGN-NR11S/S Battery .
  • This effect is based on an electro-hydrodynamic instability forming what is now called “Williams domains” inside the liquid crystal.
  • 1964: George H. Heilmeier, then working in the RCA laboratories on the effect discovered by Williams achieved the switching of colours by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal  SONY VAIO VGN-NR11M/S Battery .
  • Practical problems with this new electro-optical effect made Heilmeier continue to work on scattering effects in liquid crystals and finally the achievement of the first operational liquid crystal display based on what he called the dynamic scattering mode(DSM)  SONY VAIO VGN-NR11Z/S Battery .
  • 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  SONY VAIO VGN-NR11Z/T Battery .
  • George H. Heilmeierwas inducted in the National Inventors Hall of Fame and credited with the invention of LCD.
  • 1960s: Pioneering work on liquid crystals was undertaken in the late 1960s by the UK's Royal Radar Establishment at Malvern, England  Sony VAIO VGN-FZ21E Battery .
  • 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) Sony VAIO VGN-FW21E Battery .
  • 1970: On December 4, 1970, the twisted nematic field effect in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich andMartin Schadt (then working for the Central Research Laboratories) listed as inventors  Sony VAIO VGN-NR11S/S Battery .
  • 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  Sony VAIO VGN-NR11Z/S Battery .
  • James Fergason 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   Sony VAIO VGN-NR11M/S Battery .
  • 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 Sony VAIO VGN-NR11Z/T Battery .
  • 1972: The first active-matrix liquid crystal display panel was produced in the United States by Westinghouse, in Pittsburgh, PA.
  • 1996 Samsung develops the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2010  SONY VAIO VGN-FZ180E Battery .
  • 1997 Hitachi resurrects the In Plane Switching (IPS) technology producing the first LCD to have the visual quality acceptable for TV application.
  • 2001 Jean Paul Gaultier uses LCD technology at his 2001 fall collection fashionshow which brings LCD to mainstream SONY VAIO VGN-FZ220E Battery .
  • 2007: In the 4Q of 2007 for the first time LCD televisions surpassed CRT units in worldwide sales.
  • 2008: LCD TVs become the majority with a 50% market share of the 200 million TVs forecast to ship globally in 2008 according to Display Bank SONY VAIO VGN-FZ340E Battery .

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 SONY VAIO VGN-FZ430E Battery .

Another report on the origins and history of LCD from a different perspective has been published by Hiroshi Kawamoto, available at the IEEE History Center.

Illumination

As LCD panels produce no light of their own, they require an external lighting mechanism to be easily visible  SONY VAIO VGN-FZ460E Battery .

On most displays, this consists of a cold cathode fluorescent lamp that is situated behind the LCD panel. Passive-matrix displays are usually not backlit, but active-matrix displays almost always are, with a few exceptions such as the display in the original Gameboy Advance  SONY VAIO VGN-FZ480E Battery .

Recently, two types of LED backlit LCD displays have appeared in some televisions as an alternative to conventional backlit LCDs. In one scheme, the LEDs are used to backlight the entire LCD panel. In another scheme, a set of red, green and blue LEDs is used to illuminate a small cluster of pixels, which can improve contrast and black level in some situations  SONY VAIO VGN-FZ4000 Battery.

For example, the LEDs in one section of the screen can be dimmed to produce a dark section of the image while the LEDs in another section are kept bright. Both schemes also allows for a slimmer panel than on conventional displays  SONY VAIO VGN-FZ31E Battery.

LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have individual electrical contacts 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  SONY VAIO VGN-FZ31B Battery .

Small monochrome displays such as those found in personal organizers, electronic weighing scales, older laptop screens, and the original Nintendo Game Boy have a passive-matrix structure employing super-twisted nematic (STN) or double-layer STN (DSTN) technology (the latter of which addresses a colour-shifting problem with the former) SONY VAIO VGN-FZ31J Battery,

and colour-STN (CSTN) in which colour 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 addressedbecause the pixel must retain its state between refreshes without the benefit of a steady electrical charge SONY VAIO VGN-FZ31M Battery .

As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow response times and poor contrast are typical of passive-matrix addressed LCDs.

Monochrome passive-matrix LCDs were standard in most early laptops (although a few used plasma displays)  SONY VAIO VGN-FZ31Z Battery .

The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an active-matrix display (though still monochrome), but passive-matrix was the norm until the mid-1990s, when colour active-matrix became standard on all laptopsSONY VAIO VGN-FZ38M Battery .

High-resolution colour displays such as modern LCD computer monitors and televisions use an active matrix structure. A matrix of thin-film transistors (TFTs) is added to the polarizing and colour filters. Each pixel has its own dedicated transistor, allowing each column line to access one pixel   SONY VGP-BPS8 Battery .

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 operation  SONY VGP-BPS13/S Battery .

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  SONY VGP-BPS13A/B Battery .

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  SONY VGP-BPS13B/B Battery .

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  SONY VGP-BPS13A/S Battery .

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  SONY VGP-BPS13AS Battery .

Before LGEnhanced IPS was introduced in 2009, the additional transistors resulted in blocking more transmission area, thus requiring a brighter backlight, which consumed more power, and made this type of display less desirable for notebook computers  Dell Inspiron 1320n Battery .

This newer, lower power technology can be found in the AppleiMac, iPad, and iPhone 4, as well as the Hewlett-Packard EliteBook 8740w. Currently Panasonic is using an enhanced version eIPS for their large size LCD-TV products  Dell Inspiron 1464 Battery .

Advanced fringe field switching (AFFS)

Known as fringe field switching (FFS) until 2003, advanced fringe field switching is a technology similar to IPS or S-IPS offering superior performance and colour gamut with high luminosity. AFFS is developed by Hydis Technologies Co.,Ltd, Korea (formally Hyundai Electronics, LCD Task Force)  Dell Inspiron 1564 Battery .

AFFS-applied notebook applications minimize colour distortion while maintaining its superior wide viewing angle for a professional display. Colour shift and deviation caused by light leakage is corrected by optimizing the white gamut which also enhances white/grey reproduction  Dell Inspiron 1764 Battery .

In 2004, Hydis Technologies Co.,Ltd licenses AFFS patent to Japan's Hitachi Displays. Hitachi is using AFFS to manufacture high end panels in their product line. In 2006, HYDIS also licenses AFFS to Sanyo Epson Imaging Devices Corporation.

Hydis introduced AFFS+ which improved outdoor readability in 2007  Dell Studio 1450 Battery .

Vertical alignment (VA)

Vertical alignment displays are a form of LCDs in which the liquid crystal material naturally exists in a vertical state removing the need for extra transistors (as in IPS)  Dell Studio 1457 Battery .

When no voltage is applied, the liquid crystal cell 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        Dell Latitude D610 Battery .

VA liquid crystal displays provide some of the same advantages as IPS panels.

Blue Phase mode

Blue phase mode LCDs have been shown as engineering samples early in 2008, they are not in mass-production yet  Toshiba NB100 Battery .

The physics of blue phase mode LCDs suggest that very short switching times (~1 ms) can be achieved, so time sequential color control can possibly be realized and expensive color filters would be obsolete. For details refer to Blue Phase Mode LCD Toshiba Satellite M65 battery .

Quality control

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective transistors are usually still usableToshiba Satellite M60 battery .

It is claimed that it is economically prohibitive to discard a panel with just a few defective pixels because LCD panels are much larger than ICs, but this has never been proven. Manufacturers' policies for the acceptable number of defective pixels vary greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea Dell Latitude D830 Battery .

As of 2005, though, Samsung adheres to the less restrictive ISO 13406-2 standard.Other companies have been known to tolerate as many as 11 dead pixels in their policies.Dead pixel policies are often hotly debated between manufacturers and customers  Dell Latitude D620 Battery .

To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard.However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways  Dell Inspiron Mini 10 Battery .

LCD panels are more likely to have defects than most ICs due to their larger size. For example, 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  Sony VGN-FW11S Battery .

Due to competition between manufacturers quality control has been improved. 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  Sony VGN-FW11M Battery ,

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  Sony VGN-FW139E/H battery .

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   Dell Latitude E5400 Battery .

LCD panels also have defects known as clouding (or less commonly mura), which describes the uneven patches of changes in luminance. It is most visible in dark or black areas of displayed scenes.

Zero-power (bistable) displays

The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can retain an image without power  Dell Latitude E4200 Battery .

The crystals may exist in one of two stable orientations ("Black" and "White") and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufacture both grayscale and colour ZBD devices  Dell Inspiron 300M Battery .

A French company, Nemoptic, has developed the BiNem zero-power, paper-like LCD technology which has been mass-produced in partnership with Seiko since 2007. 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  Dell Vostro A840 Battery .

Kent Displays has also developed a "no power" display that uses Polymer Stabilized Cholesteric liquid crystal (ChLCD). A major drawback of ChLCD screens are their slow refresh rate, especially at low temperatures Dell Studio 1737 battery .

Kent has recently demonstrated the use of a ChLCD to cover the entire surface of a mobile phone, allowing it to change colours, and keep that colour even when power is cut off.

In 2004 researchers at the University of Oxford demonstrated two new types of zero-power bistable LCDs based on Zenithal bistable techniques   Dell Inspiron E1505 battery .

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 materialsDell RM791 battery .

Other bistable technologies (i.e. Binem Technology) are based mainly on the surface properties and need specific weak anchoring materials.

Specifications

Important factors to consider when evaluating a Liquid Crystal Display (LCD)  Dell XPS M1530 battery :

  • Resolution versus Range: Fundamentally resolution is the granularity (or number of levels) with which a performance feature of the display is divided. Resolution is often confused with range or the total end-to-end output of the display. Each of the major features of a display has both a resolution and a range that are tied to each other but very different Dell XPS M2010 battery .
  • Frequently the range is an inherent limitation of the display while the resolution is a function of the electronics that make the display work.
  • Spatial Performance LCDs come in only one size for a variety of applications and a variety of resolutions within each of those applications  Acer Aspire One battery .
  • LCD spatial performance is also sometimes described in terms of a “dot pitch”. The size (or spatial range) of an LCD is always described in terms of the diagonal distance from one corner to its opposite. This is a historical aspect from the early days of CRT TV when CRT screens were manufactured on the bottoms of a glass bottle  Toshiba Satellite P10 Battery .
  • The diameter of the bottle determined the size of the screen. Later, when TVs went to a more square format, the square screens were measured diagonally to compare with the older round screens.

The spatial resolution of an LCD is expressed in terms of the number of columns and rows of pixels (e.g., 1024×768) SONY VGN-FZ210CE Battery .

This had been one of the few features of LCD performance that was easily understood and not subject to interpretation. Each pixel is usually composed of a red, green, and blue sub pixel. However there are newer schemes to share sub-pixels among pixels and to add additional colours of sub-pixels  Dell Precision M70 Battery .

So going forward, spatial resolution may be more subject to interpretation.

One external factor to consider in evaluating display resolution is the resolution of your own eyes. For a normal person with 20/20 vision, the resolution of your eyes is about one minute of arc  Toshiba Satellite L305 Battery .

In practical terms that means for an older standard definition TV set the ideal viewing distance was about 8 times the height (not diagonal) of the screen away. At that distance the individual rows of pixels merge into a solid. If you were closer to the screen than that, you would be able to see the individual rows of pixels  Toshiba Satellite T4900 Battery .

If you are further away, the image of the rows of pixels still merge, but the total image becomes smaller as you get further away. For an HDTV set with slightly more than twice the number of rows of pixels, the ideal viewing distance is about half what it is for a standard definition set  Toshiba PA3399U-2BRS battery .

The higher the resolution, the closer you can sit to the set or the larger the set can usefully be sitting at the same distance as an older standard definition display.

For a computer monitor or some other LCD that is being viewed from a very close distance, resolution is often expressed in terms of dot pitch or pixels per inch Toshiba Satellite A200 Battery .

This is consistent with the printing industry (another form of a display). Magazines, and other premium printed media are often at 300 dots per inch. As with the distance discussion above, this provides a very solid looking and detailed image  Toshiba Satellite 1200 Battery .

LCDs, particularly on mobile devices, are frequently much less than this as the higher the dot pitch, the more optically inefficient the display and the more power it burns. Running the LCD is frequently half, or more, of the power consumed by a mobile device Toshiba Satellite M300 Battery .

An additional consideration in spatial performance are viewing cone and aspect ratio. The Aspect ratio is the ratio of the width to the height (for example, 4:3, 5:4, 16:9 or 16:10). Older, standard definition TVs were 4:3. Newer, HDTV’s are 16:9 as are most new notebook computers  SONY VGP-BPS13A/Q Battery .

Movies are often filmed in much different (wider) aspect ratios which is why there will frequently still be black bars at the top and bottom of a HDTV screen.

The Viewing Angle of an LCD may be important depending on its use or location  SONY VGP-BPS13A/Q Battery .

The viewing angle is usually measured as the angle where the contrast of the LCD falls below 10:1. At this point, the colours usually start to change and can even invert, red becoming green and so forth. Viewing angles for LCDs used to be very restrictive however, improved optical films have been developed that give almost 180 degree viewing angles from left to right SONY VGP-BPS13B/Q Battery .

Top to bottom viewing angles may still be restrictive, by design, as looking at an LCD from an extreme up or down angle is not a common usage model and these photons are wasted. Manufacturers commonly focus the light in a left to right plane to obtain a brighter image here  SONY VGP-BPS13B/Q Battery .

  • Temporal/Timing Performance: Contrary to spatial performance, temporal performance is a feature where smaller is better. Specifically, the range is the pixel response time of an LCD, or how quickly you can change a sub-pixel’s brightness from one level to another  SONY VGP-BPS13/Q Battery .
  • For LCD monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult. Further, this number is almost never published in sales advertising  SONY VGP-BPS13/Q Battery .

Refresh rate or the temporal resolution of an LCD is the number of times per second in which the display draws the data it is being given. Since activated LCD pixels do not flash on/off between frames, LCD monitors exhibit no refresh-induced flicker, no matter how low the refresh. rate  SONY VGP-BPS21A/B Battery .

High-end LCD televisions now feature up to 240 Hz refresh rate, which requires advanced digital processing to insert additional interpolated frames between the real images to smooth the image motion. However, such high refresh rates may not be actually supported by pixel response times and the result can be visual artifacts that distort the image in unpleasant ways SONY VGP-BPS21/S Battery .

Temporal performance can be further taxed if it is a 3D display. 3D displays work by showing a different series of images to each eye, alternating from eye to eye. For a 3D display it must display twice as many images in the same period of time as a conventional display and consequently the response time of the LCD becomes more important  SONY VGP-BPS21B Battery .

3D LCDs with marginal response times, will exhibit image smearing.

The temporal resolution of human perception is about 1/100th of a second. It is actually greater in your black and white vision (rod cells) than in colour vision (cone cells)  SONY VGP-BPS21A Battery .

You are more able to see flicker or any sort of temporal distortion in a display image by not looking directly at it as your rods are mostly grouped at the periphery of your vision.

  • Colour Performance There are many terms to describe colour performance of an LCD SONY VGP-BPS21 Battery .
  • They include colour gamut which is the range of colours that can be displayed and colour depth which is the colour resolution or the resolution or fineness with which the colour range is divided. Although colour gamut can be expressed as three pairs of numbers  Sony VGP-BPS21A/B Battery ,
  • the XY coordinates within colour space of the reddest red, greenest green, and bluest blue, it is usually expressed as a ratio of the total area within colour space that a display can show relative to some standard such as saying that a display was “120% of NTSC”  Sony VGP-BPS21/S Battery .
  • NTSC is the National Television Standards Committee, the old standard definition TV specification. Colour gamut is a relatively straight forward feature. However with clever optical techniques that are based on the way humans see colour, termed colour stretch  Sony VGP-BPS21A Battery .
  • colours can be shown that are outside of the nominal range of the display. In any case, colour range is rarely discussed as a feature of the display as LCDs are designed to match the colour ranges of the content that they are intended to show. Having a colour range that exceeds the content is a useless feature  Sony VGP-BPS21 Battery .

Colour Depth or colour support is sometimes expressed in bits, either as the number of bits per sub-pixel or the number of bits per pixel. This can be ambiguous as an 8-bit colour LCD can be 8 total bits spread between red, green, and blue or 8 bits each for each colour in a different display  Sony Vaio PCG-5G2L Battery .

Further, LCDs sometimes use a technique called dithering which is time averaging colours to get intermediate colours such as alternating between two different colours to get a colour in between. This doubles the number of colours that can be displayed; however this is done at the expense of the temporal performance of the display  Sony Vaio PCG-5G3L Battery .

Dithering is commonly used on computer displays where the images are mostly static and the temporal performance is unimportant.

When colour depth is reported as colour support, it is usually stated in terms of number of colours the LCD can show. The number of colours is the translation from the base 2-bit numbers into common base-10  Sony Vaio PCG-5J1L Battery .

For example, s 8-bit, in common terms means 2 to the 8th power or 256 colours. 8-bits per colour or 24-bits would be 256 x 256 x 256 or over 16 Million colours. The colour resolution of the human eye depends on both the range of colours being sliced and the number of slices; but for most common displays the limit is about 28-bit colour  Sony Vaio PCG-5K2L Battery .

LCD TVs commonly display more than that as the digital processing can introduce colour distortions and the additional levels of colour are needed to ensure true colours  Sony Vaio PCG-5J2L Battery .

There are additional aspects to LCD colour and colour management such as white point and gamma correction which basically describe what colour white is and how the other colours are displayed relative to white      Sony Vaio PCG-5K1L Battery .

LCD televisions also frequently have facial recognition software which recognizes that an image on the screen is a face and both adjust the colour and the focus differently from the rest of the image  Sony Vaio PCG-6S2L Battery .

These adjustments can have important impact to the consumer but are not easily quantifiable; people like what they like and everyone does not like the same thing. There is no substitute for looking at the LCD you are going to buy before buying it. Portrait film, another form of display, has similar adjustments built in to it  Sony Vaio PCG-6S3L Battery .

Many years ago, Kodak had to overcome initial rejection of its portrait film in Japan because of these adjustments. In the US, people generally prefer a more colour facial image than is reality (higher colour saturation). In Japan, consumers generally prefer a less saturated image  Sony Vaio PCG-6V1L Battery .

The film that Kodak initially sent to Japan was biased in exactly the wrong direction for Japanese consumers. TV sets have their built in biases as well     Sony Vaio PCG-6W1L Battery .

  • Brightness and Contrast ratio: Contrast Ratio is the ratio of the brightness of a full-on pixel to a full-off pixel and, as such, would be directly tied to brightness if not for the invention of the blinking backlight (or burst dimming)  Sony Vaio PCG-6W2L Battery.
  • The LCD itself is only a light valve, it does not generate light; the light comes from a backlight that is either a florescent tube or a set of LEDs. The blinking backlight was developed to improve the motion performance of LCDs by turning the backlight off while the liquid crystals were in transition from one image to another  Sony Vaio PCG-6W3L Battery .
  • However, a side benefit of the blinking backlight was infinite contrast. The contrast reported on most LCDs is what the LCD is qualified at, not its actual performance. In any case, there are two large caveats to contrast ratio as a measure of LCD performance  Sony Vaio PCG-7111L Battery .

The first caveat is that contrast ratios are measured in a completely dark room. In actual use, the room is never completely dark as you will always have the light from the LCD itself. Beyond that, there may be sunlight coming in through a window or other room lights that reflect off of the surface of the LCD and degrade the contrast  Sony Vaio PCG-7112L Battery .

As a practical matter, the contrast of an LCD, or any display, is governed by the amount of surface reflections not by the performance of the display.

The second caveat is that the human eye can only image a contrast ratio of a maximum of about 200:1  Sony Vaio PCG-7113L Battery.

Black print on a white paper is about 15-20:1. That is why viewing angles are specified to the point where the fall below 10:1. A 10:1 image is not great, but is discernable.

Brightness is usually stated as the maximum output of the LCD   Sony Vaio PCG-7133L Battery .

In the CRT era, Trinitron CRTs had a brightness advantage over the competition so brightness was commonly discussed in TV advertising. With current LCD technology, brightness, though important     Sony Vaio PCG-7Z2L Battery ,

is usually the same from maker to maker and is consequently not discussed much except for notebook LCDs and other displays that will be viewed in bright sunlight. In general, brighter is better but there is always a trade-off between brightness and battery life in a mobile device  Sony Vaio PCG-8Y1L Battery .

Military use of LCD monitors

LCD monitors have been adopted by the United States of America military instead of CRT displays because they are smaller, lighter and more efficient, although monochrome plasma displays are also used, notably for their M1 Abrams tanks  Sony Vaio PCG-8Y2L Battery .

For use with night vision imaging systems a US military LCD monitor must be compliant with MIL-L-3009 (formerly MIL-L-85762A). These LCD monitors go through extensive certification so that they pass the standards for the military  Sony Vaio PCG-8Z1L Battery .

These include MIL-STD-901D - High Shock (Sea Vessels), MIL-STD-167B - Vibration (Sea Vessels), MIL-STD-810F – Field Environmental Conditions (Ground Vehicles and Systems), MIL-STD-461E/F – EMI/RFI (Electromagnetic Interference/Radio Frequency Interference)  Sony Vaio PCG-8Z2L Battery ,

MIL-STD-740B – Airborne/Structureborne Noise, and TEMPEST - Telecommunications Electronics Material Protected from Emanating Spurious Transmissions.

Thin film transistor liquid crystal display (TFT-LCD) is a variant of liquid crystal display (LCD) which uses thin-film transistor (TFT) technology to improve image quality (e.g., addressability, contrast)  SONY VAIO VGN-FW31J Battery .

TFT LCD is one type of active matrix LCD, though all LCD-screens are based on TFT active matrix addressing. TFT LCDs are used in television sets, computer monitors, mobile phones, handheld video game systems, personal digital assistants,navigation systems, projectors, etc SONY VAIO VGN-FW31E Battery .

Small liquid crystal displays as used in calculators and other devices 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 picture elements (pixels)  SONY VAIO VGN-FW31B Battery ,

since it would require millions of connections – top and bottom connections for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions to thousands  SONY VAIO VGN-FW31M Battery .

The column and row wires attach totransistor switches, one for each pixel. The one-way current passing characteristic of the transistor prevents the charge applied to the pixel from draining between refreshes to the display image. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive ITO layers SONY VAIO VGN-FW31Z Battery .

The circuit layout process of a TFT-LCD is very similar to that of semiconductor products. However, rather than fabricating the transistors from siliconformed into a crystalline silicon wafer, they are made from a thin film of amorphous silicon deposited on a glass panel  SONY VAIO VGN-FW38M Battery .

The silicon layer for TFT-LCDs is typically deposited using the PECVD process . Transistors take up only a small fraction of the area of each pixel; the rest of the silicon film is etched away to allow light to pass through  SONY VAIO VGN-AW41JF Battery .

Polycrystalline silicon is sometimes used in displays requiring higher TFT performance. Examples include small high-resolution displays such as those found in projectors or view finders. Amorphous silicon-based TFTs are by far the most common due to their lower production cost, whereas polycrystalline silicon TFTs are more costly and difficult to produce SONY VAIO VGN-AW41JF/H Battery .

The inexpensive twisted nematic display is the most common consumer display type. The pixel response time on modern TN panels is sufficiently fast to avoid the shadow-trail and ghosting artifacts of earlier production  SONY VAIO VGN-AW41MF Battery .

The fast response time has been emphasised in advertising TN displays, although in most cases this number does not reflect performance across the entire range of possible color transitions  SONY VAIO VGN-AW41MF/H Battery .

More recent use of RTC (Response Time Compensation / Overdrive) technologies has allowed manufacturers to significantly reduce grey-to-grey (G2G) transitions, without significantly improving the ISO response time  SONY VAIO VGN-FW30B Battery .

Response times are now quoted in G2G figures, with 4ms and 2ms now being commonplace for TN-based models. The good response time and low cost has led to the dominance of TN in the consumer market  SONY VAIO VGN-FW50B Battery .

TN displays suffer from limited viewing angles, especially in the vertical direction. Colors will shift when viewed off-perpendicular. In the vertical direction, colors will shift so much that they will invert past a certain angle SONY VAIO VGN-FW51B/W Battery .

Also, most TN panels represent colors using only 6 bits per RGB color, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bittruecolor) that are available from graphics cards. Instead, these panels display interpolated 24-bit color using a dithering method that combines adjacent pixels to simulate the desired shade   SONY VAIO VGN-FW51MF Battery .

They can also use a form of temporal dithering called Frame Rate Control (FRC), which cycles between different shades with each new frame to simulate an intermediate shade. Such 18 bit panels with dithering are sometimes advertised as having "16.2 million colors"SONY VAIO VGN-FW51MF/H Battery .

These color simulation methods are noticeable to many people and highly bothersome to some. FRC tends to be most noticeable in darker tones, while dithering appears to make the individual pixels of the LCD visible. Overall, color reproduction and linearity on TN panels is poor  SONY VAIO VGN-FW51ZF Battery .

Shortcomings in display color gamut(often referred to as a percentage of the NTSC 1953 color gamut) are also due to backlighting technology. It is not uncommon for displays with simple LED orCCFL-based lighting to range from 10% to 26% of the NTSC color gamut  SONY VAIO VGN-FW51ZF/H Battery ,

whereas other kind of displays, utilizing more complicated CCFL or LED phosphorformulations or RGB LED backlights, may extend past 100% of the NTSC color gamut, a difference quite perceivable by the human eye  SONY VAIO VGN-FW52JB Battery .

The transmittance of a pixel of an LCD panel typically does not change linearly with the applied voltage, and the sRGB standard for computer monitors requires a specific nonlinear dependence of the amount of emitted light as a function of the RGB value  SONY VAIO VGN-FW54FB Battery .

In-plane switching (IPS)

In-plane switching was developed by Hitachi Ltd. in 1996 to improve on the poor viewing angle and the poor color reproduction of TN panels at that time  SONY VAIO VGN-FW70DB Battery .

Its name comes from the main difference from TN panels, that the crystal molecules move parallel to the panel plane instead of perpendicular to it. This change reduces the amount of light scattering in the matrix, which gives IPS its characteristic wide viewing angles and good color reproduction   SONY VAIO VGN-FW71DB/W Battery . 

Initial iterations of IPS technology were plagued with slow response time and a low contrast ratio but later evolutions have made marked improvements to these shortcomings. Because of its wide viewing angle and accurate color reproduction  SONY VAIO VGN-FW72JGB Battery (

with almost no off-angle color shift), IPS is widely employed in high-end monitors aimed at professional graphic artists, although with the recent fall in price it has been seen in the mainstream market as well  SONY VAIO VGN-FW73JGB Battery .

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