Liquid crystal display television (LCD TV) is, as indicated by its name, a television using LCD technology, as opposed to cathode ray or plasma [see Plasma Display explanation] for its visual output.

Early LCD panel television had some difficulties displaying fast-moving action and had quite restricted viewing angles. These problems have largely been overcome in recent years, and the market for LCD televisions is booming. For a long time it was widely believed that LCD technology was suited only to smaller sized televisions, and could not compete with plasma technology at larger sizes. This belief has been undermined by the announcements of ever-larger panels by companies such as Sharp Corporation, Samsung and LG.Philips. In October 2004, 40" to 45" televisions were widely available and Sharp Corporation had announced the successful manufacture of a 65" panel. Also in 2004, Samsung and Sony joined forces to build a factory in South Korea, intended to produce 60,000 panels a month, and in March 2005, Samsung announced an 82" HDTV TFT Panel. The main manufacturers have all pledged to invest billions of dollars in LCD production over the next few years, with televisions expected to be a key market.

• What is Contrast Ratio?

The contrast ratio is a metric of a video display, defined as the ratio of the light intensity of the brightest possible color to the darkest possible color a display is capable of displaying simultaneously. The higher the contrast ratio, the better the display is.

Examples are 800:1, 700:1, and 500:1 from higher to lower capability. Infinite contrast ratios can be achieved by devices capable of emitting no light at all as their darkest color. Contrast ratio is most commonly considered in connection with transmissive displays, such as LCD, in which all pixels share the same light emitter, and manipulate the brightness of transmitted light individually. Technological challenges make it hard to design a mechanism to shut off 100% of transmitted light in these displays. Additionally, any optics in front of the matrix of light modulators that can potentially mix the light from different pixels, such as the lens of a DLP/LCD projector, will also degradate the conrast ratio.

Emissive display technologies - where all pixels emit light individually, such as OLED, plasma, and FED - are capable of achieving a very good contrast ratio.

Poor contrast ratio manifests itself in the lack of true black, and in noticeably desaturated colors (the darker is the supposed color - the stronger is the desaturation).

There can't be too much of a contrast - that's a marketing myth, invented to sell cheap LCD displays.

A notable recent developement in the LCD technology is the so called "dynamic contrast". When there is a need to display a dark image, the display would underpower the backlight lamp (or decrease the aperture of the projector's lens using a shutter), but will proportionately amplify the transmission through the LCD panel. This gives the benefit of realizing the potential static contrast ratio of the LCD panel in dark scenes, when the image is watched in a dark room. The drawback is that if a dark scene does contain small areas of superbright light, they may be sacrificed and blown out. This may not sound too bad though, as the static contrast ratio of a human eye is just around 100 and so the details in those highlights might not be resolvable anyway. The trick for the display is to determine how much of the highlights may be unnoticeably blown out in a given image under the given ambient lighting conditions.

Note that the contrast ratio promoted in marketing literature for emissive (as opposed to reflective) displays is always measured under the optimum condition of a room in total darkness. In typical viewing situations the contrast ratio is significantly lower due to the reflection of light from the surface of the display. How much the room light reduces the contrast ratio depends on the luminance of the display, as well as the amount of light reflecting off the display.

In audio, the equivalent is dynamic range.

Universal capabilities

Modern LCD TV sets are geographically universal because they have a multisystem tuner, to display PAL, NTSC and SECAM norms. And they include an electronic (step-down & step-up) transformer that automatically can use 110/200 V AC indifferently and universal grounded adapter plugs.

Also, the vast majority are no longer just for TV and HDTV. They can also be used as a computer monitor with a VGA/DVI signal, although resolution support can vary widely.

·        Wireless AV kit (SmartLink)

Some newer LCD TV sets can connect to a host computer via a bluetooth or WiFi wireless link.

·        Teletext and Electronic Programe Guide

They generally include teletext and NexTView for EPG.

Developments in LCD televisions

TVs based on PVA and S-PVA LCD panels deliver quite good angle of view. They also deliver an adequate contrast ratio for viewing bright scenes; and also dark scenes in bright room. Dynamic contrast technique improves contrast when viewing dark scenes in a dark room. Alternatively, a TV from a creative electronics manufacturer will throw some light on the wall behind it to help making dark scenes look darker.

Moving pictures on a CRT TV do not exhibit any sort of "trails" or "ghosting" because the CRT's phosphor, charged by the strike of electrons, emits most of the light in a very short time, under 1 ms, compared with the refresh period of i.e. 20 ms (for 50 fps video). In LCDs, each pixel emits light of set intensity for a full period of 20 ms (in this example), plus the time it takes for it to switch to the next state, typically 12 to 25 ms.

The second time (called the "response time") can be shortened by the panel design (for black-to-white transitions), and by using the technique called overdriving (for black-to-gray and gray-to-gray transitions); however this only can go down to as short as the refresh period.

This is usually enough for watching film-based material, where the refresh period is so long (1/24 s, or 41.(6) ms), and judder is so strong on moving objects, that film producers actually almost always try to keep object of interest immobile in the film's frame.

Video material, shot at 50 or 60 frames a second, tries to actually capture the motion. When the eye of a viewer tracks a moving object in video, it doesn't jump to its next predicted position on the screen with every refresh cycle, but it moves smoothly; thus the TV must display the moving object in "correct" places for as often as possible, and erase it from oudated places as fast as possible.

There are two emerging techniques to solve this problem. First, the backlight of the LCD panel may be fired during the shorter period of time than the refresh period, preferrably as short as possible, and preferrably when the pixel has already settled to the intended brightness. This technique resurrects the much hated flicker problem of the CRTs, because the eye is able to sense flicker at the typical 50 or 60 Hz refresh rates.

Another approach is to double the refresh rate of the LCD panel, and reconstruct the intermediate frames using various motion compensation techniques, extensively tested on high-end "100 Hz" CRT televisions in Europe.

The best approach is probably the combination of two, possibly allowing the viewer to switch them on or off when viewing video- or film-based material.

What is Plasma Display?

·        History

The Plasma display panel was invented at the University of Illinois by Donald L. Bitzer and H. Gene Slottow in 1964 for the PLATO Computer System. The original monochrome (usually orange or green) panels enjoyed a surge of popularity in the early 1970s because the displays were rugged and needed neither memory nor refresh circuitry. There followed a long period of sales decline in the late 1970s as semiconductor memory made CRT displays incredibly cheap. Nonetheless, plasma's relatively large screen size and thin profile made the displays attractive for high-profile placement such as lobbies and stock exchanges. Fujitsu General began selling 3-color plasma displays to this lucrative niche market in 1993.

Starting with his PhD dissertation in 1975, Larry Weber of the University of Illinois sought to create a color plasma display, finally achieving that goal in 1995. Today the superior brightness and viewing angle of color plasma panels have caused these displays to have a resurgence of popularity.

General characteristics

Plasma displays are bright (1000 lx or higher for the module), have a wide color gamut, and can be produced in fairly large sizes, up to 200 cm (80 inches) diagonally. They have a very high "dark-room" contrast, creating the "perfect black", desirable for watching movies. The display panel is only 6 cm (2 1/2 inches) thick, while the total thickness, including electronics, is less than 10 cm (4 inches). Plasma displays use as much power per square meter as a CRT or a AMLCD television; in 2004 the cost has come down to US$1900 or less for the popular 42 inch (107 cm) diagonal size, making it very attractive for home-theatre use. However, since the power consumption is proportional to the square of the diagonal size, the larger screen sizes can use considerable power—"as much as 700 watts of power, enough to make some critics worry about the environmental consequences if the displays are widely adopted." The lifetime of the latest generation of PDPs is estimated at 60,000 hours to half life when displaying video. Half life is the point where the picture has degraded to half of its original brightness and intensity, which is considered the end of the functional life of the display.

Competing displays include the Cathode ray tube, OLED, AMLCD, DLP, SED-tv and field emission flat panel displays. The main advantage of plasma display technology is that a very wide screen can be produced using extremely thin materials. Since each pixel is lit individually, the image is very bright and looks good from almost every angle. Because many plasma displays still have a lower resolution the image quality is often not quite up to the standards of good LCD displays or cathode ray tube sets, but it certainly meets most people's expectations. The biggest drawbacks of plasma technology are the high cost, often lower resolution, and relatively short lifespan. With prices starting around US$2,000 and going all the way up past US$20,000 (as of 2004), these sets do not sell as quickly as older technologies like CRT. But as prices fall and technology advances, they may start to seriously compete against the CRT sets.

Functional details

The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, on both sides of the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate.

In a monochrome plasma panel, control circuitry charges the electrodes that cross paths at a cell, causing the plasma to ionize and emit photons between the electrodes. The ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.

To ionize the gas in a color panel, the plasma display's computer charges the electrodes that intersect at that cell thousands of times in a small fraction of a second, charging each cell in turn. When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.

The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel. By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel color to create hundreds of different combinations of red, green and blue. In this way, the control system can produce colors across the entire visible spectrum. Plasma displays use the same phosphors as CRTs, accounting for the extremely accurate color reproduction.

Contrast ratio claims

Contrast ratio indicates the difference between the brightest part of a picture and the darkest part of a picture, measured in discrete steps, at any given moment. The implication is that a higher contrast ratio means more picture detail. Contrast ratios for plasma displays are often advertised as high as 5000:1. On the surface, this is a great thing. In reality, there are no standardised tests for contrast ratio, meaning each manufacturer can publish virtually any number that they like. To illustrate, some manufacturers will measure contrast with the front glass removed, which accounts for some of the wild claims regarding their advertised ratios. For reference, the page you're reading now (on a computer monitor) is actually about 50:1. A printed page is about 80:1. A really good print at a movie theater will be about 500:1 (Da-Lite, Angles of View vol. III, "Contrast - From Dark to Light").

What is HDTV?