LCD TV

What exactly is a Liquid Crystal Diode (LCD) TV?
LCDs are all around us. Liquid crystal displays so prevalent, in fact, that most people couldn't get through their day without using one. This technology is utilized in digital clocks, microwave ovens, car dashboards, calculators, stereos, thermometers, and even some bathroom scales! The applications for liquid crystal displays are almost limitless, so it should come as no surprise that this technology has revolutionized the most basic home appliance of all-the television set.

How does a LCD (Liquid Crystal Diode) TV operate?
The Basics: LCD monitors work by blocking light. By sandwiching a solution of TN liquid crystals between two perpendicularly aligned panes of polarized glass, it becomes possible to manipulate the intensity of light as it passes through this crystalline matrix and out the glass panel at the other end. Depending on the voltage of the electrical charge running through them, liquid crystals will untwist so that the intensity of light able to pass through the second polarized pane is affected. 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 gray scale in between.

Addressing: A liquid crystal display consists of an array of tiny segments-called "pixels"-that are manipulated to form images or to present information. Addressing is the process by which pixels are turned on (which disables the passage of light) and off (which enables the passage of light) so as to create an image on the polarized display pane in front of you. So-called active-matrix LCD TVs employ thin film transistors (TFTs), or tiny switching transistors and capacitors arranged in a matrix on a glass substrate, to direct electric charges down columns to reach a particular pixel. This, in turn, causes the liquid crystals to untwist and "display" a predetermined amount of light generated by the light source-usually a florescent bulb-in back of them.

Color (Re) Production: 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 color. To achieve a full color pallet on your LCD display, each pixel is divided into three subpixels-red, green, and blue-that work in conjunction to determine the LCD pixel's overall hue. These subpixels are created by subtracting certain wavelengths, and the color(s) corresponding thereto, using special filters. By exploiting a combination of red, green, and blue subpixels of various intensities (or gray scales), a single pixel triad can reproduce approximately 16.8 million colors.

Besides looking cool and oh-so futuristic in your living room, what are the advantages of owning an LCD TV or monitor?

It's easier to watch. Flat-panel displays like LCDs and Plasmas are significantly brighter and feature higher contrasts than traditional CRT sets. Which 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.

And, you can watch TV from almost anywhere in a room since flat-screen LCD displays can have up to a 160° viewing angle, which means your TV will look good when viewed from any point 80° in either direction from the center of the display.

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 subpixels of the same color in adjoining pixel triads. 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 millimeters (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 displays have long been touted as having wider viewing angles than comparably sized LCD monitors. But recent improvements in quality have made LCD televisions and monitors comparable to Plasma TVs with respect to their viewing angles. According to Sharp, a leading manufacturer of LCDs, the newest generation of LCD displays have just as good viewing angles as plasma sets, but this is only true of the better brands. In any event, even the best LCD monitors have yet to achieve the breadth of viewing angles found on typical Plasma monitors.

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're more or less plug-and-play devices. Since most LCD TVs don't require external tuning devices, they are ideal for smaller applications, where space is at a premium (like bedrooms and small living rooms) or where clutter is inconvenient (like crowed kitchen countertops).

Note: Some LCD televisions have outboard media receivers, though many-like Toshibas-don't. Always inquire about extra hardware before you buy: You won't always see your LCD monitor pictured with an external receiver (even if it has one), so it's up to you to find out whether there is any "extra" hardware you need to know about.

The picture is smooth, colorful, and (best of all) wide. LCDs have none of those annoying scan lines that conventional sets do. This owes to the fact that each subpixel 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 color. [256 shades of red x 256 shades of green x 256 shades of blue " 16.8 million different colors!]

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 subpixel 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 clocking in with response times under 20ms. Slower response times (>20ms) can cause the image on the panel to lag and appear jerky, an effect known as "streaking" or "trailing." 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.

LCD displays come either with a 16:9 aspect ratio (i.e., 16 units wide to 9 units high), the proper one for viewing HDTV and for watching DVDs, or with a 4:3 aspect ratio, the norm for most broadcast television shows. If you opt to go with a widescreen (16:9) display, does this mean that you'll have to watch some shows where the image is distorted or stretched unnaturally? No. When displaying a "normal" or 4:3 picture image from satellite, VCR, or cable TV, the image can be viewed in a number of ways-in its original format (with black or gray bars on the sides of the screen), or in "full" mode (where the image is converted or "stretched" using specially designed algorithms to reduce the visible stretch marks as much as possible). Again, the quality of the picture produced under such circumstances depends largely on the quality of the television with which you scale-up 4:3 pictures or scale-down 16:9 ones. Nevertheless, this is only a temporary dilemma: Since HDTV is shown in widescreen, this is the format of the future for much of broadcast television.

The display is multi-functional and long-lived. An LCD is a television monitor, capable of displaying HDTV, regular TV, and home video. It's also a computer monitor. In fact, it can accept any video format. LCD displays typically include inputs for (a) composite video, (b) S-video and component video, and (c) one or more RGB inputs from a computer. 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.

Note: Some LCDs (including many by Sharp) do not come with RGB inputs. If you plan to utilize your LCD display as a computer monitor, be sure to check out the specs of the unit you're thinking of purchasing.

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 watching TV was your full-time job, and you did it 24 hours a day, it would take you almost 7 years to wear out your LCD display. With more normal viewing habits of, say, 8 hours per day, you can extend the lifespan of your TV by a decade or more (to about 20 years)!

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, colors 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, Toshiba, JVC, or Sony than you will for cheap Chinese or Korean variety knock-offs, but you'll get a backlighting bulb of higher quality and, in the end, a TV whose colors 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.