A Guide to LCD TVs and Monitors
LCDs are all around us; utilised in digital clocks, microwave ovens, car dashboards, calculators, stereos, thermometers, etc. The applications for liquid crystal displays (LCD) are almost limitless, so it is not surprising that this technology has also revolutionised the television set.
How does a LCD (Liquid Crystal Diode) TV operate?
LCD monitors work by blocking light. Basically, these displays can switch between light states (where the liquid crystals are fully twisted) and dark states (where the liquid crystals are fully untwisted), or somewhere along the grey scale in between.
A liquid crystal display (LCD) consists of an array of tiny segments called ‘pixels’ that are manipulated to form images or to present information.
The light source in an active-matrix LCD monitor is a florescent bulb, which emits white light through a polarized glass pane behind the liquid crystal solution. Theoretically, then, you can start with a white display: This is one where its liquid crystals are completely twisted and therefore able to direct the full spectrum of light out through the polarized display screen in front of you. Since all wavelengths can pass through, the full spectrum of light can be manipulated to create the desired colour. To achieve a full colour pallet on your LCD display, each pixel is divided into three sub-pixels-red, green, and blue that work in conjunction to determine the LCD pixel's overall hue.
What are the advantages of LCD Displays?
It's easier to watch. Flat panel TV displays like LCDs and Plasmas are significantly brighter and feature higher contrasts than traditional CRT sets. This means that an LCD TV will perform exceedingly well under most ambient light conditions. A brightly lit room won't wash out its picture, nor will lamplight cause a glare on your television screen. The beauty of these flat screens is that you don't have to turn out the lights to see the image clearly and easily. Nor do you have to worry about eyestrain, since neither LCDs nor Plasmas flicker the way old-fashioned TVs do.
One issue affecting the overall quality of the picture reproduced on LCDs has to do with dot pitch. This term refers to the distance between sub-pixels of the same colour in adjoining pixels. The closer these "dots" are to one another, the sharper the resolution will be. This is especially true when displaying computer signal images and graphs. And the picture in front of you will be more realistic and detailed. Higher dot pitches also increase the viewing angles of LCD panels. Since dot pitch is measure in millimetres (mm), a good rule of thumb is this: Smaller dot pitches make for sharper images. You generally want a dot pitch of .28mm [10,000 pixels/in2 of your display] or finer.
Note: Plasma TV displays have long been touted as having wider viewing angles than comparably sized LCD monitors. Potentially, the screen image becomes washed out in contrast if not viewed from directly in front of the screen. Recent improvements in quality have made some LCD televisions and monitors comparable to Plasma TVs with respect to their viewing angles but this is sometimes only true of the better brands. Before buying your LCD of choice it is recommended that you review the model in a showroom and position yourself at a number of angles to the screen comparable to your common viewing angles.
You can watch your new television right out of the box because the tuner is included. LCD TVs generally come with tuners and speakers already built in, so they are more or less plug-and-play devices. Since most LCD TVs do not require external tuning devices, they are ideal for smaller applications, where space is at a premium (like bedrooms and small living rooms).
The picture is smooth, colourful, and (best of all) wide. LCDs have none of those annoying scan lines that conventional sets do. This owes to the fact that each sub-pixel has its own transistor electrode, which creates smooth, evenly lit images across the entire surface of the display. It also enables these displays to reproduce images that are saturated with colour. [256 shades of red x 256 shades of green x 256 shades of blue = 16.8 million different colours!]
Note: All this requires an enormous number of transistors-upwards of 2.4 million for displays supporting a typical resolution of, say, 1024x768. This means that, if there is a problem with any one of these transistors, a sub-pixel will be affected, which causes the pixel associated with it to fail. Dead pixels will emerge over time and with use. In general, though, the number of dead pixels affecting a given display will be few enough so as to go virtually unnoticed by the average viewer.
Recent advances in LCD technology have markedly increased the response time of these displays, resulting in even smoother on-screen presentations. One way to think about response time is in terms of the amount of time it takes a pixel to refresh itself i.e. to go from being active to being inactive, which is to say, ready to be re-activated. Response time is measured in milliseconds (ms), with the best LCD monitors now meeting response times under 20ms. Slower response times (>20ms) can cause the image on the panel to lag and appear jerky. Another phenomenon associated with slower response times is ghosting. This occurs when the display is made to switch quickly from light to dark states (or vice-versa). In these instances, on-screen images may appear to stay on the screen belatedly.
The display is multi-functional. An LCD is a television monitor, capable of displaying HDTV, standard TV, and home video. It is also a computer monitor. In fact, it can accept most video format, assuming your screen has the appropriate sockets. LCD displays typically include inputs for (a) composite video, (b) S-video and component video, (c) one or more RGB inputs from a computer and (d) HDMI or DVI inputs for HDTV. Because of the high resolution of LCDs, text and graphics look especially sharp when viewed on them, which makes them the best solution for displaying data and web-based content.
You can expect to use your LCD monitor in many capacities for many years: The average lifespan of one of these displays is 60,000 hours. If you watched TV 24 hours a day, it would take you almost 7 years to wear out your LCD display.
Note: The lifespan of an LCD display is generally longer than that of similar-sized plasma displays. Some manufacturers claim that their LCDs can last upwards of 80,000 hours when used continuously under controlled conditions (e.g., in a room with "standard" lighting conditions and 77° temperatures throughout). Just how realistic such claims are is debatable. After all, whose living room has no windows and remains at a perfectly comfortable 77 degrees year-round?
A more immediate concern is the actual lifespan of the light source in your LCD. This is perhaps THE critical component of your display unit. It is particularly important for maintaining a proper white balance on your TV. As these florescent bulbs age, colours can become unbalanced, which could result in too much red, for example, in your picture. So, it pays to buy name-brand displays. You will definitely pay more for better LCD display brands like Sharp, Panasonic, Pioneer, Toshiba, JVC, or Sony as you will get a backlighting bulb of higher quality and, in the end, a TV whose colours will stay truer longer.
In some cases, the warranty for this particular feature can be shorter than for the display as a whole. This means you might have to buy a whole new LCD monitor because the coverage on its backlight has expired. Moreover, some bulbs can be replaced, while others are built in to the unit itself. You should definitely do some research on the backlighting system, how it's configured, and how it's warranted.
Pros & Cons of LCD Technology
Pros
Cons
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Of all the fixed-pixel technologies, LCD has the biggest problem producing true blacks. Some light always passes through when the liquid crystals untwist, so the best black on most LCD panels is a very dark grey.
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Because of the way light passes through an LCD cell, direct-view LCDs usually have a narrower viewing angle than plasma TVs.
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Low-resolution LCDs exhibit distinct pixilation and screen-door effects when blown up to big screen sizes. For front projection, using a model with XGA (1,024 x 768) or higher resolution will reduce screen-door effects.
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