The History & Development of LCD Monitors

Introduction

In 1970, Fergason made the first operating LCD. Prior to this invention, LCD used a large amount of power, provided a limited life, and had poor visual contrast. In 1971, the first LCD were demonstrated publicly and enthusiastically accepted. LCD stands for Liquid Crystal Display are organic substances that reflect light when voltage is applied. The liquid crystal display consists of a liquid suspension between two glass or plastic panels. Crystals in this suspension are naturally aligned parallel with one another, allowing light to pass through the panel. When electric current is applied, the crystals change orientation and block light instead of allowing it pass through, turning the crystal region dark. LCD monitors are typically found in laptop computers, or inside multimedia projectors. Most flat-panel desktop computer monitors are based on LCD technology.

However, early version of liquid crystals were unstable and unsuitable for mass production. Only when a British scientist discovered "Biphenyl", a stable liquid crystal material, that made it possible for LCD technology to take off. The first generation LCD appeared on calculators, then game sets and watches.

LCD Monitors Today

Today's LCD monitors are known as flat-panel, dual scan, active matrix and thin film transistor, TFT. LCD monitors have been around for more than 30 years, but due to low research and development in the past, LCD monitors have a bad reputation in providing good picture quality. LCD monitors are increasingly in demands today and the popularity is from its Sleek looks, slim waist, cool looks, take up less space, lightweight, low power usage(about 15-30watts) and also known to be own by the rich and famous.

As time passes, the price falls and the LCD monitors are providing better quality in terms of brightness, clearness and sharpness. This is the main reason consumers and end-users are switching from the conventional CRT to LCD. Previous LCD technologies were slower, less efficient, and provided lower contrast. The oldest of the matrix technologies, passive-matrix, offers sharp text but leaves ghost images on the screen when the display changes rapidly, making it less than optimal for motion video. Today, most black-and-white palmtops, pagers, and mobile phones use passive-matrix LCD. Because LCDs address each pixel individually, they can create sharper text than CRTs, which, when badly focused, blur the distinct pixels that make up the screen image.

There are two kinds of LCD: DSTN (dual-scan twisted nematic) and TFT (thin film transistor), which are also known as passive and active matrix displays. LCD is made of several layers that are arranged according to the following order: Polarising filter, Sheet of glass, Electrode, Alignment layer, Liquid crystals, Alignment layer, Electrode, Sheet of glass, Polarising filter.

The earliest laptops used 8-inch (diagonal) passive-matrix black-and-white screens. But as LCD monitors evolved toward active matrix, display sizes grew. Today's LCD almost exclusively use TFT-based panels, which can provide bright, sharp displays in much larger sizes.

How an LCD works?

The cross-section of the TFT LCD panel looks like a multi-layer sandwich. At the outermost layer on either side are clear glass substrates. Between the substrates are the thin film transistor, colour filter panel that provides you the necessary red, blue and green primary colours, and the liquid crystal layer. Completing the LCD is a fluorescent backlight that illuminates the screen from beneath.

Under normal conditions when there is no electrical charge, the liquid crystals are in an amorphous state. In this state, the liquid crystal pass through. By subjecting the liquid crystal layer to varying amount of electrical charges, the liquid crystal layer will allow different amount of light to pass through, as they orientate themselves according to the control center for the liquid crystals.

Just like in an ordinary CRT, the red, green and blue liquid crystal "chambers"; make up one pixel (picture element). By subjecting the red, green, blue chambers to varying degrees of electrical charges, different colours can be achieved.

An entire TFT screen is made up of a grid of pixel, with each pixel having a transistor turning it on or off. This is where you get your resolution. Thus, for an LCD to provide a screen resolution 1024 x 768 pixel (SVGA), it must have that number of pixels.

Why Choose an LCD Monitor

LCD monitors have a new sense of style. Traditional cathode-ray-tube displays had a standardized form factor, owing to the required shape of the heavy vacuum tube. Free from the bulky shape of the CRT, today's flat panel vendors are letting their imaginations run free with monitors that are colored and shaped to match a design concept.

Compare a 15-inch deep, 30-pound CRT against a panel that's less than 7 inches deep (including the base) and weighs 12 or 13 pounds, and it's easy to see the advantages of LCD monitors. They don't have a CRT's geometric, convergence, or focus problems, and their clarity makes it easier to view higher resolutions at smaller screen sizes. For example, even 17-inch LCD monitor 1280 x 1024 well; 18-inch monitors generally aren't usable above 1280 x 1024. Also, the latest LCD monitors are all digital, unlike CRTs. This means that graphics cards with digital outputs don't have to convert the graphics information into analog form as they would with a typical monitor. Theoretically, this makes for more accurate color information and pixel placement. In contrast, LCD that plug into standard analog VGA ports actually have to perform a second conversion back to digital (because LCD panels are digital devices), which can result in distracting artifacts. Now that the industry's Digital Display Working Group has finally settled on a standard and more graphics cards will be shipping with digital options, it will be easier to choose an all-digital solution.

The advantages of LCD monitors

• LCD monitors consume less power
• Do not produce electromagnetic radiation as CRTs do
• Do not flicker like CRTs
• Are light and slim in size
• Full viewable size

Other differences:

• Resolutions: CRTs are able to display more resolutions than LCD monitors which have only one resolution at full screen size. Lower resolutions are possible by using only a part of the screen. If a panel with 1024 x 768 resolution needs to display a resolution of 640 x 480 it uses only 66% of the screen.
• Diagonal measurement: LCD's viewable area is the same as its diagonal measurement. CRTs lose about an inch behind the faceplate or bezel. Convergence: In LCD monitors, each cell is switched on or off individually so there is no convergence problems as in CRTs in which use electron guns and need faultless
• Signals: CRTs require analogue and LCD monitors require digital signals.
• Do not flicker: You will get a high quality image with very little eyestrain due to the flat screen and do not flicker display.

How to choose a LCD monitor?

"Don't judge a book by its cover", and in buying a LCD, apply the same wisdom as well. Most first time buyers would taken in by its looks, but more importantly, evaluate carefully the following features to ensure that a LCD is worth buying.

• Dead pixels - A flat panel may contain some "dead" or faulty pixels. These are usually easy to spot: they show a constant colour. Dead pixels are the result of the manufacturing process and they cannot be "revived". Acceptable count is less than three dead pixels per screen. But for some, dead pixels can be irritating, especially if you use the flat panel to watch movies. If you cannot accept dead pixels, make sure you check the screen first before buying.
• Viewing angle - If you have used notebook computer before, you'll know that the LCD offers the best view when you look at it at a certain angle. Some LCD monitors have wide viewing angles, thereby enabling you to see what's on the screen even if don't view it directly in front of you. However, some people find narrow view angles in notebook computers useful, since they prevent other sitting close to you to see what's on your screen. Above 120 degree is considered good.
• Contrast ratio - The LCD doesn't emit light on its own but relies on a backlight to illuminate the screen. A dark screen doesn't mean the backlight isn't working; the pixel merely block off the light from transmitted through the liquid crystal layer. The contrast ratio is measure of how many brightness levels the LCD can have. Generally, a contrast ratio of over 250:1 is considered good.
• Brightness - How bright can an LCD be? The truth is, the LCD can be brighter than a CRT. But generally, the maximum brightness of the LCD is around 225 candelas per square meter - compared to the brightness of a TV screen.
• Screen size - Like conventional CRTs, the LCD is also measured in terms of its diagonal screen size. However, take a note that the LCD doesn't have a black border like the CRT. Thus, a 15.1" LCD shows full 15.1" screen (which typically is 1024 x 768 pixel resolution). A 17.1" LCD will show 1280 x 1024 pixel resolution.

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