Friday, January 9, 2009

Monitor Types


CRT stands for cathode ray tube describing the technology inside an analog computer monitor or television set. A CRT monitor or TV is readily recognizable by its bulky form. LCD monitors and plasma television sets, or flat panel displays, use newer digital technologies. The CRT monitor creates a picture out of many rows or lines of tiny colored dots. These are technically not the same thing as pixels, but the terms are often used interchangeably. The more lines of dots per inch, the higher and clearer the resolution. Therefore 1024 x 768 resolutions will be sharper than 800 x 600 resolutions because the former uses more lines creating a denser, more detailed picture. Higher resolutions are important for displaying the subtle detail of graphics. For text, resolution isn't as critical.

Working principal of Monitor.

Inside a CRT monitor is a picture tube that narrows at the rear into a bottleneck. In the bottleneck is a negative charged filament or cathode enclosed in a vacuum. When electricity is supplied, the filament heats up and a stream or "ray" of electrons pours off the element into the vacuum. The negatively charged electrons are attracted to positively charged anodes which focus the particles into three narrow beams, accelerating them to strike the phosphor-coated screen. Phosphor will glow when exposed to any kind of radiation, absorbing ultraviolet light and emitting visible light of fluorescent color. Phosphors that emit red, green and blue light are used in a color monitor, arranged as "stripes" made up of dots of color. The three beams are used to excite the three colors in combinations needed to create the various hues that form the picture.To precisely direct the beams, copper steering coils are used to create magnetic fields inside the tube. The fields move the electron beams vertically or horizontally. By applying varying voltages to the steering coils, a beam can be positioned at any point on the screen. Each image is painted on the screen -— and repainted -- several times each second by scanning the electron beams across the screen at incredible rates. This must be done even when the picture being displayed is unchanging, because the phosphor only glows for a very short time.The refresh rate indicates how many times per second the screen is repainted. Though monitors differ in their capabilities, lower resolutions normally have higher refresh rates because it takes less time to paint a lower resolution. Therefore a setting of 800 x 600 might have a refresh rate of 85Hz, (the screen will be repainted or refresh 85 times per second), while a resolution setting of 1024 x 768 may have a refresh rate of 72Hz. Still higher resolutions usually have refresh rates closer to 60Hz. Anything less than 60Hz is generally considered inadequate, and some people will detect "flicker" even with acceptable refresh rates. Generally speaking, high-end monitors have higher refresh rates overall than lower-end models.Another specification regarding CRT monitors is "dot pitch" which relates to the tightness or sharpness of the picture. A lower dot pitch such as .25 is preferable over a higher dot pitch. In the heydey of the CRT monitor this was an issue because some models were sold with .32 dot pitch, resulting in "fuzzy" text. By the end of the CRT era, virtually all displays had .28 or better and today's CRT monitors can have dot pitches as low as .21.The CRT monitor comes in 15-inch to 21-inch sizes (38 — 53 cm) and larger, though the actual viewing screen is about 1 inch (2.5 cm) smaller than the rated size. Screens are measured diagonally from corner to corner, including the case.

LCD/Flat panel Monitors

Short for liquid crystal display, LCD technology can be found in digital watches and computer monitors. LCD displays use two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light. Color LCD displays use two basic techniques for producing color: Passive matrix is the less expensive of the two technologies. The other technology, called thin film transistor (TFT) or active-matrix, produces color images that are as sharp as traditional CRT displays, but the technology is expensive.

TFT Flat Panel Monitor

TFT (Thin Film Transistor) is fast becoming the new LCD monitor standard due to an increased level of screen resolution and image sharpness. The manufacturers simply apply a thin transistor to the screen, allowing greater pixel control.This can benefit all applications with demands on visual quality, including computer games or the display of a wide range of fonts. Most LCD monitors you will encounter when searching online stores or in high street shops will now be TFT.


Resolution & Viewing Quality

Resolution on a CRT is flexible and a newer model will provide you with viewing resolutions of up to 1600 by 1200 and higher, whereas on an LCD the resolution is fixed within each monitor (called a native resolution). The resolution on an LCD can be changed, but if you're running it at a resolution other than its native resolution you will notice a drop in performance or quality.

Both types of monitors (newer models) provide bright and vibrant color display. However, LCDs cannot display the maximum color range that a CRT can. In terms of image sharpness, when an LCD is running at its native resolution the picture quality is perfectly sharp. On a CRT the sharpness of the picture can be marked by soft edges or a faulty focus.

A CRT monitor can be viewed from almost any angle, but with an LCD this is often a problem. When you use an LCD, your view changes as you move different angles and distances away from the monitor. At some odd angles, you may notice the picture fade, and possibly look as if it will disappear from view.

Refresh Rate

Some users of a CRT may notice a bit of an annoying flicker, which is an inherent trait, based on CRTs physical components. Today's graphics cards, however, can provide a high refresh rate signal to the CRT to get rid of this otherwise annoying problem. LCDs are flicker-free and as such the refresh rate isn't an important issue with LCDs.

Dot Pitch

Dot pitch refers to the space between the pixels that make up the images on your screen, and is measured in millimeters. The less space between pixels, the better the image quality. On either type of monitor, smaller dot pitch is better and you're going to want to look at something in the 0.26 mm dot pitch or smaller range.

Screen (viewable) Size

Most people today tend to look at a 17-inch CRT or bigger monitor. When you purchase a 17-inch CRT monitor, you usually get 16.1 inches or a bit more of actual viewing area, depending on the brand and manufacturer of a specific CRT. The difference between the "monitor size" and the "view area" is due to the large bulky frame of a CRT. If you purchase a 17" LCD monitor, you actually get a full 17" viewable area, or very close to a 17".

Physical Size

There is no denying that an LCD wins in terms of its physical size and the space it needs. CRT monitors are big, bulky and heavy. They are not a good choice if you're working with limited desk space, or need to move the monitor around (for some odd reason) between computers. An LCD on the other hand is small, compact and lightweight. LCDs are thin, take up far less space and are easy to move around. An average 17-inch CRT monitor could be upwards of 40 pounds, while a 17&-inch LCD would weigh in at around 15 pounds.


As an individual one-time purchase an LCD monitor is going to be more expensive. Throughout a lifetime, however, LCDs are cheaper as they are known to have a longer lifespan and also lower power consumption. The cost of both technologies has come down over the past few years, and LCDs are reaching a point where smaller monitors are within many consumers' price range. You will pay more for a 17" LCD compared to a 17" CRT, but since the CRT's actual viewing size is smaller, it does bring the question of price back into proportion.


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