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LCD: The Dominator
According to figures from Displaysearch, almost 88 percent of all screens manufactured in 2008 were LCDs, of which 35 percent were passive-matrix versions, the simplest types of displays, and 53 percent were active-matrix. This is followed by vacuum fluorescent displays (VFD) with 6.6 percent, while cathode-ray tube screens still manage 2.5 percent. The whole screen market is around 3.8 billion units, of which only around 220 million are intended for use in TVs.
In the year 2008, LCD overtook CRT on the TV market, worldwide and according to quantity - in terms of sales, on the other hand, it had been ahead for some time. Even in the big-screen formats of 40" (102 cm) and above, LCD has become the market leader. 50" (127 cm) sets are still headed up by plasma and the 60-inch-and-over (>152 cm) class remains firmly back-projector territory.
The TV market is, however, still driven more by supply, and less by demand: What can be produced is also sold. The fact that LCD is marching ahead, and will continue to do so, is largely because the corresponding factories have been built, and must now be operated at full capacity.
A characteristic of LCD production is that the factories must always be constructed to suit a specific size of glass - otherwise, unused area that costs to manufacture simply becomes waste. Therefore, it is economically crucial to choose these sizes correctly for production.
The substrates are divided into generations, with production of TV displays beginning only from the fifth generation (5G) onward. Smaller units are primarily used for mobile displays.
• 5G denotes a glass size of 1.1 x 1.3 meters, initially also 1.0 x 1.2 meters: 5.5G denotes 1.3 x 1.5 meters.
• 6G generally measures 1.5 x 1.85 meters.
• 7G begins at 1.87 x 2.2 meters, and 7.5G is 1.95 x 2.25 meters.
• 8G describes sizes from 2.16 x 2.4 to 2.2 x 2.5 meters. Furthermore, there are projects in place for Generation 10, which currently denotes 2.88 x 3.08 meters. Speculation continues about 11G (3.2 x 3.6 meters).
Manufacture at sensible prices is possible if at least six panels of the desired size can be cut from one substrate. 5G factories were initially used primarily for 26" (66 cm) to 30" (76 cm), and, since then, mostly for notebook and PC monitor panels. 6G factories are especially suited to 32" (81 cm) and 37" (94 cm), which provide eight or six panels respectively, or twelve 26-inchers. 7G and 7.5G are ideal for 40/42 inches and 46/47 inches respectively. Even larger substrates can be worthwhile, if planning TV sizes over 50" - but also because they allow higher flexibility in production, with less unused area.
The size of the so-called "mother glass" determines the economic viability of an LCD's manufacture. Here, workers present a substrate used in the P6 factory of LG.Philips-LCD (now LG Display) - eight 32 inch screens can be cut from this.
The most important problems of LCDs - which previously stood in the way of their use in TVs - can now be seen as solved, from a technological point of view. The reaction times are now sufficiently short to produce no blur (less than 15 milliseconds), and manufacturers are using 100 Hertz technology (or 120 Hz in NTSC countries) for even clearer motion, and sometimes already even 200 Hz (240 Hz for NTSC). Pulsed backlighting also makes movement sharper, as the eye then sees hard edges. The degradation of the picture when viewed at an angle is being combated with the special technologies ASV, IPS and MVA/PVA.
"Advanced Super-View" from Sharp arranges the crystals concentrically (Continuous Pinwheel Alignment), which makes the emission suitably uniform, ASV is sometimes seen as a variant of VA. But, even the basic version "Twisted Nematic" (TN) or also "Super Twisted Nematic" (STN) has gained significantly thanks to newer filters and light directing technologies, so that most PC monitors, as well as normal TV screens, are now produced as variants of TN.
For illumination, manufacturers generally choose the cheap Cold-Cathode Fluorescent Lamps (CCFL), while LEDs are already on the advance in notebooks and in particularly expensive TVs. With LEDs, you gain a number of advantages. For example, a considerably extended color space can be achieved if you use red, green and blue diodes. Some manufacturers use white LEDs, for cost reasons. The first TV screens are now switching over to LEDs.
Also, they are practically continuously adjustable, so the backlight can be adjusted to match the required illumination of the picture, allowing almost infinitely high contrast ratios to be realized, since a fully black picture can be displayed without any light behind it. The contrast within the picture (measured as the ANSI contrast, for example) cannot, of course, match this. CCFL backlights can also be dimmed, but so far only down to around ten or twenty percent.
With LEDs it is also relatively cost-effective to pulse the backlight (called scanning or blinking backlight). This allows considerably sharper motion depiction, because the lamps are only active for a fraction of the time that each picture is displayed. The eye therefore perceives significantly less blur. Instead, this creates a sharp edge in the moment when the image flashes, and the eye can use this to orientate itself. Light output is not lost due to the pulsing.
Some screens use a specialty of LED backlighting known as "local dimming", which allows the backlight to be varied for different areas of the picture. The individual light sources are controlled either in blocks or individually, and provide only the amount of light required by the picture, significantly improving the contrast that can be achieved within one picture.
Thanks to the continuous and localized adjustability, these LCD screens consume distinctly less power. And, since CCFL tubes are not being used, the devices no longer contain mercury, which was only still permitted thanks to a special exemption.
Using LEDs for the backlight improves many of the properties of LCDs - for example the reproduction of colors and motion.
The newest trend in the year 2008 are the so-called "Slim LCDs". Up till now, the casings of the units have always been between eight and twelve centimeters deep, whereas the new generation brings this down to between one and four centimeters.
The key to making the devices slimmer is almost always the light unit. To begin with, there are new types of filters and light diffusion layers that allow quite a few centimeters to be saved by achieving uniform brightness even at short viewing distances. LEDs contribute partly to this, since they are thinner than fluorescent tubes. In very thin devices the lamps are positioned to one side and direct the light diffusely behind the panel.
There are also new approaches to producing particularly energy-efficient screens. One first step is to integrate light sensors that adjust the picture's brightness to suit the ambient illumination. Local dimming also plays an important part, but special energy-saving screens take other approaches, for example with particularly economical fluorescent tubes, which also sit relatively far from the liquid crystal layer. This means less light sources are required, and less light is lost into the diffusion layers.