Liquid crystal display television
Encyclopedia
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s that use LCD display technology to produce images. LCD televisions are thinner and lighter than cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRTs) of similar display size, and are available in much larger sizes. When manufacturing costs fell, this combination of features made LCDs practical for television receivers.
In 2007, LCD televisions surpassed sales of CRT-based televisions worldwide for the first time, and their sales figures relative to other technologies are accelerating. LCD TVs are quickly displacing the only major competitors in the large-screen market, the plasma display panel
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
and rear-projection television
Rear-projection television
Rear-projection television or RPTV is a type of large-screen television display technology. Up until the mid-2000s, most of the relatively affordable consumer large screen TVs up to used rear-projection technology...
. LCDs are, by far, the most widely produced and sold television display type.
LCDs also have a variety of disadvantages. Other technologies address these weaknesses, including organic light-emitting diode
Organic light-emitting diode
An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s (OLED), FED
Field emission display
A field emission display is a display technology that incorporates flat panel display technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor to produce a color image as a electronic visual display...
and SED
Surface-conduction Electron-emitter Display
A surface-conduction electron-emitter display is a display technology which is currently developing various flat panel displays by a number of companies as a electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image...
, but none of these have entered widespread production.
Basic LCD concepts
Cold cathode
A cold cathode is a cathode used within nixie tubes, gas discharge lamps, discharge tubes, and some types of vacuum tube which is not electrically heated by the circuit to which it is connected...
s (CCFLs) at the back of the screen, although some displays use white or colored LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s instead. Millions of individual LCD shutters, arranged in a grid, open and close to allow a metered amount of the white light through. Each shutter is paired with a colored filter to remove all but the red, green or blue (RGB) portion of the light from the original white source. Each shutter–filter pair forms a single sub-pixel. The sub-pixels are so small that when the display is viewed from even a short distance, the individual colors blend together to produce a single spot of color, a pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
. The shade of color is controlled by changing the relative intensity of the light passing through the sub-pixels.
Liquid crystal
Liquid crystal
Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...
s encompass a wide range of (typically) rod-shaped polymers that naturally form into thin layers, as opposed to the more random alignment of a normal liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
. Some of these, the nematic liquid crystals, also show an alignment effect between the layers. The particular direction of the alignment of a nematic liquid crystal can be set by placing it in contact with an alignment layer or director, which is essentially a material with microscopic grooves in it. When placed on a director, the layer in contact will align itself with the grooves, and the layers above will subsequently align themselves with the layers below, the bulk material taking on the director's alignment. In the case of an LCD, this effect is utilized by using two directors arranged at right angles and placed close together with the liquid crystal between them. This forces the layers to align themselves in two directions, creating a twisted structure with each layer aligned at a slightly different angle to the ones on either side.
LCD shutters consist of a stack of three primary elements. On the bottom and top of the shutter are polarizer
Polarizer
A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined polarization. The common types of polarizers are linear polarizers and circular...
plates set at right angles. Normally light cannot travel through a pair of polarizers arranged in this fashion, and the display would be black. The polarizers also carry the directors to create the twisted structure aligned with the polarizers on either side. As the light flows out of the rear polarizer, it will naturally follow the liquid crystal's twist, exiting the front of the liquid crystal having been rotated through the correct angle, that allows it to pass through the front polarizer. LCDs are normally transparent.
To turn a shutter off, a voltage is applied across it from front to back. the rod-shaped molecules align themselves with the electric field instead of the directors, destroying the twisted structure. The light no longer changes polarization as it flows through the liquid crystal, and can no longer pass through the front polarizer. By controlling the voltage applied across the crystal, the amount of remaining twist can be selected. This allows the transparency of the shutter to be controlled. To improve switching time, the cells are placed under pressure, which increases the force to re-align themselves with the directors when the field is turned off.
Several other variations and modifications have been used in order to improve performance in certain applications. In-Plane Switching displays (IPS and S-IPS) offer wider viewing angles and better color reproduction, but are more difficult to construct and have slightly slower response times. IPS displays are used primarily for computer monitors. Vertical Alignment (VA, S-PVA and MVA) offer higher contrast ratio
Contrast ratio
The contrast ratio is a property of a display system, defined as the ratio of the luminance of the brightest color to that of the darkest color that the system is capable of producing...
s and good response times, but suffer from color shifting when viewed from the side. In general, all of these displays work in a similar fashion by controlling the polarization of the light source.
Addressing sub-pixels
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
would be opaque, LCDs use electrodes made of a transparent conductor, typically indium tin oxide
Indium tin oxide
Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...
.
Since addressing a single shutter requires power to be supplied to an entire row and column, some of the field always leaks out into the surrounding shutters. Liquid crystals are quite sensitive, and even small amounts of leaked field will cause some level of switching to occur. This partial switching of the surrounding shutters blurs the resulting image. Another problem in early LCD systems was the voltages needed to set the shutters to a particular twist was very low, but that voltage was too low to make the crystals re-align with reasonable performance. This resulted in slow response time
Response time
In technology, response time is the time a system or functional unit takes to react to a given input.- Data processing :In data processing, the response time perceived by the end user is the interval between the instant at which an operator at a terminal enters a request for a response from a...
s and led to easily visible "ghosting" on these displays on fast-moving images, like a mouse cursor on a computer screen. Even scrolling text often rendered as an unreadable blur, and the switching speed was far too slow to use as a useful television display.
In order to attack these problems, modern LCDs use an active matrix
Active matrix
Active matrix is a type of addressing scheme used in flat panel displays. The term describes a method of switching individual elements of a flat panel display, using a CdSe or Silicon-based thin-film transistor for each pixel...
design. Instead of powering both electrodes, one set, typically the front, is attached to a common ground. On the rear, each shutter is paired with a thin-film transistor
Thin-film transistor
A thin-film transistor is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid...
that switches on in response to widely separated voltage levels, say 0 and +5 volts. A new addressing line, the gate line, is added as a separate switch for the transistors. The rows and columns are addressed as before, but the transistors ensure that only the single shutter at the crossing point is addressed; any leaked field is too small to switch the surrounding transistors. When switched on, a constant and relatively high amount of charge flows from the source line through the transistor and into an associated capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
. The capacitor is charged up until it holds the correct control voltage, slowly leaking this through the crystal to the common ground. The current is very fast and not suitable for fine control of the resulting store charge, so pulse code modulation is used to accurately control the overall flow. Not only does this allow for very accurate control over the shutters, since the capacitor can be filled or drained quickly, but the response time of the shutter is dramatically improved as well.
Building a display
A typical shutter assembly consists of a sandwich of several layers deposited on two thin glass sheets forming the front and back of the display. For smaller display sizes (under 30 inches), the glass sheets can be replaced with plastic.The rear sheet starts with a polarizing film, the glass sheet, the active matrix components and addressing electrodes, and then the director. The front sheet is similar, but lacks the active matrix components, replacing those with the patterned color filters. Using a multi-step construction process, both sheets can be produced on the same assembly line. The liquid crystal is placed between the two sheets in a patterned plastic sheet that divides the liquid into individual shutters and keeps the sheets at a precise distance from each other.
The critical step in the manufacturing process is the deposition of the active matrix components. These have a relatively high failure rate, which renders those pixels on the screen "always on". If there are enough broken pixels, the screen has to be discarded. The number of discarded panels has a strong effect on the price of the resulting television sets, and the major downward fall in pricing between 2006 and 2008 was due mostly to improved processes.
To produce a complete television, the shutter assembly is combined with control electronics and backlight. The backlight for small sets can be provided by a single lamp using a diffuser or frosted mirror to spread out the light, but for larger displays a single lamp is not bright enough and the rear surface is instead covered with a number of separate lamps. Achieving even lighting over the front of an entire display remains a challenge, and bright and dark spots are not uncommon.
Packaging
In a CRT the electron beam is produced by heating a metal filament, which "boils" electrons off its surface. The electrons are then accelerated and focused in an electron gunElectron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
, and aimed at the proper location on the screen using electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
s. The majority of the power budget of a CRT goes into heating the filament, which is why the back of a CRT-based television is hot. Since the electrons are easily deflected by gas molecules, the entire tube has to be held in vacuum. The atmospheric force on the front face of the tube grows with the area, which requires ever-thicker glass. This limits practical CRTs to sizes around 30 inches; displays up to 40 inches were produced but weighed several hundred pounds, and televisions larger than this had to turn to other technologies like rear-projection.
The lack of vacuum in an LCD television is one of its advantages; there is a small amount of vacuum in sets using CCFL backlights, but this is arranged in cylinders which are naturally stronger than large flat plates. Removing the need for heavy glass faces allows LCDs to be much lighter than other technologies. For instance, the Sharp LC-42D65, a fairly typical 42-inch LCD television, weighs 55 lbs including a stand, while the late-model Sony KV-40XBR800, a 40" 4:3 CRT weighs a massive 304 lbs without a stand, almost six times the weight.
LCD panels, like other flat panel display
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s, are also much thinner than CRTs. Since the CRT can only bend the electron beam through a critical angle while still maintaining focus, the electron gun has to be located some distance from the front face of the television. In early sets from the 1950s the angle was often as small as 35 degrees off-axis, but improvements, especially computer assisted convergence, allowed that to be dramatically improved and, late in their evolution, folded. Nevertheless, even the best CRTs are much deeper than an LCD; the KV-40XBR800 is 26 inches deep, while the LC-42D65U is less than 4 inches thick – its stand is much deeper than the screen in order to provide stability.
LCDs can, in theory, be built at any size, with production yields being the primary constraint. As yields increased, common LCD screen sizes grew, from 14 to 30", to 42", then 52", and 65" sets are now widely available. This allowed LCDs to compete directly with most in-home projection television sets, and in comparison to those technologies direct-view LCDs have a better image quality. Experimental and limited run sets are available with sizes over 100 inches.
Efficiency
LCDs are relatively inefficient in terms of power use per display size, because the vast majority of light that is being produced at the back of the screen is blocked before it reaches the viewer. To start with, the rear polarizer filters out over half of the original un-polarized light. Examining the image above, you can see that a good portion of the screen area is covered by the cell structure around the shutters, which removes another portion. After that, each sub-pixel's color filter removes the majority of what is left to leave only the desired color. Finally, to control the color and luminance of a pixel as a whole, the light has to be further absorbed in the shutters. 3M suggests that, on average, only 8 to 10% of the light being generated at the back of the set reaches the viewer.For these reasons the backlighting system has to be extremely powerful. In spite of using highly efficient CCFLs, most sets use several hundred watts of power, more than would be required to light an entire house with the same technology. As a result, LCD televisions end up with overall power usage similar to a CRT of the same size. Using the same examples, the KV-40XBR800 dissipates 245 W, while the LC-42D65 dissipates 235 W. Plasma displays are worse; the best are on par with LCDs, but typical sets draw much more.
Modern LCD sets have attempted to address the power use through a process known as "dynamic lighting" (originally introduced for other reasons, see below). This system examines the image to find areas that are darker, and reduces the backlighting in those areas. CCFLs are long cylinders that run the length of the screen, so this change can only be used to control the brightness of the screen as a whole, or at least wide horizontal bands of it. This makes the technique suitable only for particular types of images, like the credits at the end of a movie. In 2009 some manufacturers made some TVs using HCFL (more power efficient than CCFL). Sets using LEDs are more distributed, with each LED lighting only a small number of pixels, typically a 16 by 16 patch. This allows them to dynamically adjust brightness of much smaller areas, which is suitable for a much wider set of images.
Another ongoing area of research is to use materials that optically route light in order to re-use as much of the signal as possible. One potential improvement is to use microprisms or dichromic mirrors to split the light into R, G and B, instead of absorbing the unwanted colors in a filter. A successful system would improve efficiency by three times. Another would be to direct the light that would normally fall on opaque elements back into the transparent portion of the shutters. A number of companies are actively researching a variety of approaches, and 3M currently sells several products that route leaked light back toward the front of the screen.
Several newer technologies, OLED, FED and SED, have lower power use as one of their primary advantages. All of these technologies directly produce light on a sub-pixel basis, and use only as much power as that light level requires. Sony has demonstrated 36" FED units displaying very bright images drawing only 14 W, less than 1/10 as much as a similarly sized LCD. OLEDs and SEDs are similar to FEDs in power terms. The dramatically lower power requirements make these technologies particularly interesting in low-power uses like laptop computers and mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
s. These sorts of devices were the market that originally bootstrapped LCD technology, due to its light weight and thinness.
Image quality
Image Quality
Image quality is a characteristic of an image that measures the perceived image degradation . Imaging systems may introduce some amounts of distortion or artifacts in the signal, so the quality assessment is an important problem.-In photographic imaging:In digital or film-based photography, an...
, most notably the ghosting on fast-moving images, poor contrast ratio, and muddy colors. In spite of many predictions that other technologies would always beat LCDs, massive investment in LCD production, manufacturing, and electronic image processing has addressed many of these concerns.
Response time
For 60 frames per second video, common in North America, each pixel is lit for 17 ms before it has to be re-drawn (20 ms in Europe). Early LCD displays had response times on the order of hundreds of milliseconds, which made them useless for television. A combination of improvements in materials technology since the 1970s greatly improved this, as did the active matrix techniques. By 2000, LCD panels with response times around 20 ms were relatively common in computer roles. This was still not fast enough for television use.A major improvement, pioneered by NEC
NEC
, a Japanese multinational IT company, has its headquarters in Minato, Tokyo, Japan. NEC, part of the Sumitomo Group, provides information technology and network solutions to business enterprises, communications services providers and government....
, led to the first practical LCD televisions. NEC noticed that liquid crystals take some time to start moving into their new orientation, but stop rapidly. If the initial movement could be accelerated, the overall performance would be increased. NEC's solution was to boost the voltage during the "spin up period" when the capacitor is initially being charged, and then dropping back to normal levels to fill it to the required voltage. A common method is to double the voltage, but halve the pulse width, delivering the same total amount of power. Named "Overdrive" by NEC, the technique is now widely used on almost all LCDs.
Another major improvement in response time was achieved by adding memory to hold the contents of the display – something that a television needs to do anyway, but was not originally required in the computer monitor role that bootstrapped the LCD industry. In older displays the active matrix capacitors were first drained, and then recharged to the new value with every refresh. But in most cases, the vast majority of the screen's image does not change from frame to frame. By holding the before and after values in computer memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
, comparing them, and only resetting those sub-pixels that actually changed, the amount of time spent charging and discharging the capacitors was reduced. Moreover the capacitors are not drained completely; instead, their existing charge level is either increased or decreased to match the new value, which typically requires fewer charging pulses. This change, which was isolated to the driver electronics and inexpensive to implement, improved response times by about two times.
Together, along with continued improvements in the liquid crystals themselves, and by increasing refresh rates from 60 Hz to 120 and 240 Hz, response times fell from 20 ms in 2000 to about 2 ms in the best modern displays. But even this is not really fast enough because the pixel will still be switching while the frame is being displayed. Conventional CRTs are well under 1 ms, and plasma and OLED displays boast times on the order of 0.001 ms.
One way to further improve the effective refresh rate is to use "super-sampling", and it is becoming increasingly common on high-end sets. Since the blurring of the motion occurs during the transition from one state to another, this can be reduced by doubling the refresh rate of the LCD panel, and building intermediate frames using various motion compensation
Motion compensation
Motion compensation is an algorithmic technique employed in the encoding of video data for video compression, for example in the generation of MPEG-2 files. Motion compensation describes a picture in terms of the transformation of a reference picture to the current picture. The reference picture...
techniques. This smooths out the transitions, and means the backlighting is turned on only when the transitions are settled. A number of high-end sets offer 120 Hz (in North America) or 100 Hz (in Europe) refresh rates using this technique. Another solution is to only turn the backlighting on once the shutter has fully switched. In order to ensure that the display does not flicker, these systems fire the backlighting several times per refresh, in a fashion similar to movie projection where the shutter opens and closes several times per frame.
Contrast ratio
Even in a fully switched-off state, liquid crystals allow some light to leak through the shutters. This limits their contrast ratios to about 1600:1 on the best modern sets, when measured using the ANSI measurement (ANSI IT7.215-1992). Manufacturers often quote the "Full On/Off" contrast ratio instead, which is about 25% greater for any given set.This lack of contrast is most noticeable in darker scenes. To display a color close to black, the LCD shutters have to be turned to almost full opacity, limiting the number of discrete colors they can display. This leads to "posterizing" effects and bands of discrete colors that become visible in shadows, which is why many reviews of LCD TVs mention the "shadow detail". For contrast, the highest-end LCD TVs offer regular contrast ratios of 2,000,000:1.
Since the total amount of light reaching the viewer is a combination of the backlighting and shuttering, modern sets can use "dynamic backlighting" to improve the contrast ratio and shadow detail. If a particular area of the screen is dark, a conventional set will have to set its shutters close to opaque to cut down the light. However, if the backlighting is reduced by half in that area, the shuttering can be reduced by half, and the number of available shuttering levels in the sub-pixels doubles. This is the main reason high-end sets offer dynamic lighting (as opposed to power savings, mentioned earlier), allowing the contrast ratio across the screen to be dramatically improved. While the LCD shutters are capable of producing about 1000:1 contrast ratio, by adding 30 levels of dynamic backlighting this is improved to 30,000:1.
However, the area of the screen that can be dynamically adjusted is a function of the backlighting source. CCFLs are thin tubes that light up many rows (or columns) across the entire screen at once, and that light is spread out with diffusers. The CCFL must be driven with enough power to light the brightest area of the portion of the image in front of it, so if the image is light on one side and dark on the other, this technique cannot be used successfully. Displays backlit by full arrays of LEDs have an advantage, because each LED lights only a small patch of the screen. This allows the dynamic backlighting to be used on a much wider variety of images. Edge-lit displays do not enjoy this advantage. These displays have LEDs only along the edges and use a light guide plate covered with thousands of convex bumps that reflect light from the side-firing LEDs out through the LCD matrix and filters. LEDs on edge-lit displays can be dimmed only globally, not individually.
The massive on-paper boost this method provides is the reason many sets now place the "dynamic contrast ratio" in their specifications sheets. There is widespread debate in the audio-visual world as to whether or not dynamic contrast ratios are real, or simply marketing speak. Reviewers commonly note that even the best LCD displays cannot match the contrast ratios or deep blacks of plasma displays, in spite of being rated, on paper, as having much higher ratios.
Color gamut
Color on an LCD television is produced by filtering down a white source and then selectively shuttering the three primary colors relative to each other. The accuracy and quality of the resulting colors are thus dependent on the backlighting source and its ability to evenly produce white light. The CCFLs used in early LCD televisions were not particularly white, and tended to be strongest in greens. Modern backlighting has improved this, and sets commonly quote a color space covering about 75% of the NTSC 1953 color gamutGamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...
. Using white LEDs as the backlight improves this further.
In September 2009 Nanoco Group announced that it had signed a joint development agreement with a major Japanese electronics company under which it will design and develop quantum dots for use in LED backlights in LCD televisions. Quantum dots are valued for displays, because they emit light in very specific Gaussian distributions. This can result in a display that more accurately renders the colors that the human eye can perceive. Quantum dots also require very little power since they are not color filtered.
History
Early efforts
Passive matrix LCDs first became common in the 1980s for various portable computer roles. At the time they competed with plasma displays in the same market space. The LCDs had very slow refresh rates that blurred the screen even with scrolling text, but their light weight and low cost were major benefits. Screens using reflective LCDs required no internal light source, making them particularly well suited to laptop computers.Refresh rates of early devices were too slow to be useful for television. Portable televisions were a target application for LCDs. LCDs consumed far less battery power then even the miniature tubes used in portable televisions of the era. The earliest commercially made LCD TV was the Casio TV-10 made in 1983. Resolutions were limited to standard definition, although a number of technologies were pushing displays towards the limits of that standard; Super VHS offered improved color saturation, and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s added higher resolutions as well. Even with these advances, screen sizes over 30" were rare as these formats would start to appear blocky at normal seating distances when viewed on larger screens. Projection systems were generally limited to situations where the image had to be viewed by a larger audience.
Nevertheless, some experimentation with LCD televisions took place during this period. In 1988, Sharp Corporation introduced the first commercial LCD television, a 14" model. These were offered primarily as boutique items for discerning customers, and were not aimed at the general market. At the same time, plasma displays could easily offer the performance needed to make a high quality display, but suffered from low brightness and very high power consumption. However, a series of advances led to plasma displays outpacing LCDs in performance improvements, starting with Fujitsu's improved construction techniques in 1979, Hitachi's improved phosphors in 1984, and AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
's elimination of the black areas between the sub-pixels in the mid-1980s. By the late 1980s, plasma displays were far in advance of LCDs.
High-definition
It was the slow standardization of high definition television that first produced a market for new television technologies. In particular, the wider 16:9 aspect ratioAspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
of the new material was difficult to build using CRTs; ideally a CRT should be perfectly circular in order to best contain its internal vacuum, and as the aspect ratio becomes more rectangular it becomes more difficult to make the tubes. At the same time, the much higher resolutions these new formats offered were lost at smaller screen sizes, so CRTs faced the twin problems of becoming larger and more rectangular at the same time. LCDs of the era were still not able to cope with fast-moving images, especially at higher resolutions, and from the mid-1990s the plasma display was the only real offering in the high resolution space.
Through the halting introduction of HDTV in the mid-1990s into the early 2000s, plasma displays were the primary high-definition display technology. However, their high cost, both manufacturing and on the street, meant that older technologies like CRTs maintained a footprint in spite of their disadvantages. LCD, however, was widely considered to be unable to scale into the same space, and it was widely believed that the move to high-definition would push it from the market entirely.
This situation changed rapidly. Contrary to early optimism, plasma displays never saw the massive economies of scale
Economies of scale
Economies of scale, in microeconomics, refers to the cost advantages that an enterprise obtains due to expansion. There are factors that cause a producer’s average cost per unit to fall as the scale of output is increased. "Economies of scale" is a long run concept and refers to reductions in unit...
that were expected, and remained expensive. Meanwhile, LCD technologies like Overdrive started to address their ability to work at television speeds. Initially produced at smaller sizes, fitting into the low-end space that plasmas could not fill, LCDs started to experience the economies of scale that plasmas failed to achieve. By 2004, 32" models were widely available, 42" sets were becoming common, and much larger prototypes were being demonstrated.
Market takeover
1080p
1080p is the shorthand identification for a set of HDTV high-definition video modes that are characterized by 1080 horizontal lines of resolution and progressive scan, meaning the image is not interlaced as is the case with the 1080i display standard....
support, while plasmas were stuck at 720p
720p
720p is the shorthand name for 1280x720, a category of High-definition television video modes having a resolution of 1080 or 720p and a progressive scan...
, which made up for the price difference.
Predictions that prices for LCDs would drop rapidly through 2007 led to a "wait and see" attitude in the market, and sales of all large-screen televisions stagnated while customers watched to see if this would happen. Plasmas and LCDs reached price parity in 2007, at which point the LCD's higher resolution was a winning point for many sales. By late 2007, it was clear that LCDs were going to outsell plasmas during the critical Christmas sales season. This was in spite of the fact that plasmas continued to hold an image quality advantage, but as the president of Chunghwa Picture Tubes noted after shutting down their plasma production line, "Globally, so many companies, so many investments, so many people have been working in this area, on this product. So they can improve so quickly."
When the sales figures for the 2007 Christmas season were finally tallied, pundits were surprised to find that LCDs had not only outsold plasma, but also outsold CRTs during the same period. This evolution drove competing large-screen systems from the market almost overnight. Plasma had overtaken rear-projection systems in 2005. The same was true for CRTs, which lasted only a few months longer; Sony ended sales of their famous Trinitron
Trinitron
Trinitron is Sony's brand name for its line of aperture grille based CRTs used in television sets and computer display monitors. One of the first truly new television systems to enter the market since the 1950s, the Trinitron was announced in 1966 to wide acclaim for its bright images, about 25%...
in most markets in 2007, and shut down the final plant in March 2008. The February 2009 announcement that Pioneer Electronics was ending production of the plasma screens was widely considered the tipping point in that technology's history as well.
LCD's dominance in the television market accelerated rapidly. It was the only technology that could scale both up and down in size, covering both the high-end market for large screens in the 40 to 50" class, as well as customers looking to replace their existing smaller CRT sets in the 14 to 30" range. Building across these wide scales quickly pushed the prices down across the board.
In 2008, LCD TV shipments were up 33 percent year-on-year compared to 2007 to 105 million units.
In 2009, LCD TV shipments raised to 146 million units (69% from the total of 211 million TV shipments).
In 2010, LCD TV shipments reached 187.9 million units (from an estimated total of 247 million TV shipments).
Current sixth-generation panels by major manufacturers such as Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, Sharp Corporation
Sharp Corporation
is a Japanese multinational corporation that designs and manufactures electronic products. Headquartered in Abeno-ku, Osaka, Japan, Sharp employs more than 55,580 people worldwide as of June 2011. The company was founded in September 1912 and takes its name from one of its founder's first...
, LG Display, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
and the Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
have announced larger sized models:
- In October 2004, Sharp announced the successful manufacture of a 65" panel.
- In March 2005, Samsung announced an 82" LCD panel.
- In August 2006, LG Display Consumer Electronics announced a 100" LCD television
- In January 2007, Sharp displayed a 108" LCD panel under the AQUOS brand name at CES in Las Vegas.
Recent research
Some manufacturers are also experimenting with extending color reproduction of LCD televisions. Although current LCD panels are able to deliver all sRGB colors using an appropriate combination of backlight's spectrum and optical filters, manufacturers want to display even more colors. One of the approaches is to use a fourth, or even fifth and sixth color in the optical color filter array. Another approach is to use two sets of suitably narrowband backlightBacklight
A backlight is a form of illumination used in liquid crystal displays . As LCDs do not produce light themselves , they need illumination to produce a visible image...
s (e.g. LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s), with slightly differing colors, in combination with broadband optical filters in the panel, and alternating backlights each consecutive frame.
Fully using the extended color gamut will naturally require an appropriately captured material and some modifications to the distribution channel. Otherwise, the only use of the extra colors would be to let the looker boost the color saturation of the TV picture beyond what was intended by the producer, but avoiding the otherwise unavoidable loss of detail ("burnout") in saturated areas.
Competing systems
In spite of LCD's current dominance of the television field, there are several other technologies being developed that address its shortcomings. Whereas LCDs produce an image by selectively blocking a backlight OLED, FED and SED all produce light directly on the front face of the display. In comparison to LCDs, all of these technologies offer better viewing angles, much higher brightness and contrast ratio (as much as 5,000,000:1), and better color saturation and accuracy, and use less than 1/10 as much power. In theory, they are less complex and less expensive to build.Actually manufacturing these screens has proved more difficult than originally imagined. Sony abandoned their FED project in March 2009, but continue work on their OLED sets. Canon continues development of their SED technology, but announced that they will not attempt to introduce sets to market for the foreseeable future.
Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
has been displaying OLED sets at 14.1, 31 and 40 inch sizes for some time, and at the SID 2009
Society for Information Display
The Society for Information Display is an industry organization for displays, generally electronic displays such as televisions and computer monitors. SID was founded in 1962. Its main activities are publishing technical journals and running Display Week, its main conference, held in May each year...
trade show in San Antonio
San Antonio, Texas
San Antonio is the seventh-largest city in the United States of America and the second-largest city within the state of Texas, with a population of 1.33 million. Located in the American Southwest and the south–central part of Texas, the city serves as the seat of Bexar County. In 2011,...
they announced that the 14.1 and 31 inch sets are "production ready".
Environmental effects
The production of LCD screens uses nitrogen trifluorideNitrogen trifluoride
Nitrogen trifluoride is the inorganic compound with the formula NF3. This nitrogen-fluorine compound is a colorless, toxic, odourless, nonflammable gas. It finds increasing use as an etchant in microelectronics.-Applications:...
(NF3) as an etching fluid during the production of the thin-film components. NF3 is a potent greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
, and its extensive half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
may make it a potentially harmful contributor to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
. A report in Geophysical Research Letters suggested that its effects were theoretically much greater than better-known sources of greenhouse gasses like carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. As NF3 was not in widespread use at the time, it was not made part of the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...
s and has been deemed "the missing greenhouse gas".
Critics of the report point out that it assumes that all of the NF3 produced would be released to the atmosphere. In reality, the vast majority of NF3 is broken down during the cleaning processes; two earlier studies found that only 2% to 3% of the gas escapes destruction after its use. Furthermore, the report failed to compare NF3's effects with what it replaced, perfluorocarbon, another powerful greenhouse gas, of which anywhere from 30% to 70% escapes to the atmosphere in typical use.
See also
- AmbilightAmbilightAmbilight, which is short for Ambient Lighting Technology, is a feature invented by Philips Electronics, generating light effects around the TV that correspond to the video content. The effect, the company claims, is a larger virtual screen and a more immersive viewing experience. In addition,...
, Philips Electronics technology - Comparison of display technologiesComparison of display technologyThis is a comparison of various properties of different display technologies.- General characteristics :- Temporal characteristics :Different display technologies have vastly different temporal characteristics, leading to claimed perceptual differences for motion, flicker, etc.The figure shows a...
- Large-screen television technologyLarge-screen television technologyLarge-screen television technology developed rapidly in the late 1990s and 2000s. Various thin screen technologies are being developed, but only the liquid crystal display , plasma display and Digital Light Processing were released on the public market...
- LED TV
- SonySony, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
- Pixel Plus
- QuattronQuattronQuattron is the brand name of an LCD color display technology produced by Sharp Electronics. The technology utilizes a fourth color subpixel, yellow, in addition to the standard RGB color subpixels, which Sharp claims increases the range of displayable colors, and which may mimic more closely the...
, an LCD TV technology from Sharp which utilizes a fourth pixel color, yellow - TFT-LCDTFT LCDThin film transistor liquid crystal display is a variant of liquid crystal display which uses thin-film transistor technology to improve image quality . TFT LCD is one type of Active matrix LCD, though all LCD-screens are based on TFT active matrix addressing...
, a detailed discussion of LCD panels technology
External links
- Plasma is better than LCD? according to PanasonicPanasonicPanasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
in 2006 - Performance and technology of LED TV and LCD TV compared according to SonySony, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
in 2011