Monitors

Monitors

The advance of flat screen monitors is now unstoppable. The clear advantage of LCDs (Liquid Crystal Display) over CRTs is that they generate the image with the help of liquid crystals. The orientation of these crystals is modified through changes in voltage, so that they either reflect the light or let it pass through. This way, no tubes are needed to generate the image. And the list of advantages goes on: LCDs need less power than CRTs and generally have a larger optical screen size. This way, a 19'' LCD will have a "larger" visible image area than a 19'' CRT. Moreover, an image from a flat screen will lack flicker and distortion because it is not generated line by line, but all at once. In addition, LC-monitors are not subjected to magnetic fields. CRTs, which generate images via a cathode ray tube, are hence being displaced slowly but steadily by their flat-screened brethren. CRTs are bulky and heavy in comparison to flat screens. In tests, almost only the very best CRTs can keep up with LCDs. The great majority of conventional monitors have not stood up well to the advantages of LCDs - except for their comparatively affordable price. However, this small advantage is fading visibly as LCD prices keep falling.

Trends and development

For some time, things evolved at breakneck speeds towards larger screens, with correspondingly larger screen sizes. However, the screens have now reached a size that could definitely be described as the maximum reasonable size, given that home users seldom need screens larger than 22'', even less so in the case of solid CRTs. There are certainly different views on this depending of the audience: for gamers who play a lot on the computer, screens are never big enough, while on the other hand the general public can do perfectly with 19'' screens for study and work purposes. Therefore, the current trend goes mainly towards improving the imaging properties. In CRT displays this concerns mainly the refresh rate or frequency, since it is directly related to flicker, which is not only annoying, but also unhealty for the eyes. The larger the screen, the higher the refresh rate must be, something which in the largest screens is reaching the limits of technical feasibility. Flat screens have a similar characteristic: their reaction time. This determines the speed with which the liquid crystals are realigned. If it's too low, fast-moving objects can cause unsightly streaks and image blur. In addition to this, contrast and brightness in particular are factors which are constantly being improved, and which are the only significant weaknesses of LCDs so far.

Totally new approaches: SED and OLED

But technological development in the monitor field is not restricted to the two main competitors, CRT and LCD. There are new technologies being developed which should in turn replace LCD in flat screens in the not too distant future. One of the contenders for this position is SED technology, which stands for Surface-conduction Electron-emitter Display. A SED is similar to a conventional picture tube except that a single electron beam is used for each subpixel. Unlike CRT, however, SED manages without a bulky electron beam deflection tube. This allows for correspondingly large displays for wall mounting. These new screens combine the best features of CRTs and LCDs: their efficiency is very high so they consume low power, they have amazing contrast capabilities and reaction times, unlike LCDs they produce pure blacks thanks to their lack of backlighting, and they are totally flat. However, there are always disadvantages: SEDs can only display one resolution, still pictures can burn the screen the same as with CRTs and they generate X-rays. These points are particularly important in the PC arena, so it's still not clear to what extent these monitors will find wide distribution.

Not to be overlooked either is the development of diode-operated screens, OLEDs (Organic Light-Emitting Diode). Strictly speaking, the term in this denomination refers only to the kind of diodes used here: OLEDs are tiny light-emitting diodes made of organic semiconductor materials which can be produced relatively inexpensively. OLED screens have excellent viewing angles (up to 170 degrees), are even flatter than previous monitors and require less energy. Thanks to their special properties they are even bendable, which makes flexible monitors possible. OLED technology is therefore perhaps the best suited to revolutionize the world of PC screens.

Still crucial: refresh rate and reaction time

Those wanting to buy a new monitor should not be fooled by the endless columns of specifications pitched by the manufacturer. When looking for a CRT instead of an LCD, the emphasis should be placed mainly on three aspects: refresh rate, contrast and brightness. The bigger the monitor, the higher the refresh rate must be in order to avoid annoying flicker. As a general rule, for screens up to 19'' in size the rate should be around 85 Hz, while for larger monitors it should definitely be 100 Hz or more. The monitor's maximum capacity should also be considered: the closer to its maximum frequency the monitor must operate, the worse the image quality and the shorter the life of the device. Contrast is acceptable from values of 1:300 onwards, but the more the better. The same applies to brightness, which should be at least 200 candelas per square meter.

If preferences go towards a TFT monitor, reaction time, contrast and brightness should likewise be considered. While for the latter a value of 200 cd/m² is, as with CRTs, acceptable, contrast should be at least 1:400 to be able to speak of a good monitor. Special care must be paid to the reaction time: manufacturers are happy to advertise only the values when switching between black and white - but this is irrelevant in most cases. Much more important is the ability to switch between different shades of grey, and these values should be well below the ones for B&W changes. The response here should never exceed 8 milliseconds, since otherwise the human eye will perceive streaks in fast moving images and objects. For gamers, for whom extreme graphic loads are the rule, the response should be even less than 5 milliseconds.

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