onitors are often an afterthought in the purchase of computer systems. But the price of a monitor can be the largest single-cost item in a PC. Chosen carefully, a good monitor will outlast a computer system and can be passed on to be used with an upgraded system. Choosing the wrong monitor, however, can lower a user's productivity.

One serious problem that affects productivity is eyestrain. Workers' compensation claims have risen dramatically in the last few years, and the amounts of awards both in these claims and i n injury suits have risen to such levels that human resources departments are becoming involved in making sure that the monitors chosen for purchase are easy on employees' eyes.

Better monitors can produce other benefits as well. For instance, a user trying to move data between different screens in an accounting program or cut and paste between word processing documents will spend a lot longer switching between documents on the cramped screen of a 15-inch monitor than on the roomy real estate of a 21-inch model.

Users may be able to work faster with better monitors in other ways, too. In a study done by Dr. James E. Sheedy, a clinical professor and chief of the VDT/ Occupational Vision Clinic at the University of California, Berkeley, reading performance improved by 33.7% and visual comfort improved by 66% when subjects used a 1,600-by-1,200-pixel, 21-inch monitor running at 67 Hz, as opposed to a 640-by-480 pixel, 14-inch monitor running at 60 Hz. Those little bits of time add up quickly enough to ju stify the additional cost of a high-end graphics card and 21-inch monitor (about $1,600 more than a basic video card and 14-inch monitor) in relatively short order, given the salaries that skilled workers earn.

High-end displays usually will provide a longer life span as well-300,000 hours mean time between failure (MTBF) is not an uncommon figure for big monitors, while many of the smaller, inexpensive monitors that can't deliver similar reliability don't even publish their MTBF figures.

For the most part, monitors haven't changed much recently. Compared with the growth in disk capacity, memory size, and CPU performance, the changes in monitor technologies seem to be progressing at a snail's pace. Monitors are based on technology that's over 50 years old and relatively unchanged in that time. Consequently, monitor prices are not dropping as fast as the cost of other components.

The basic monitor is a large vacuum tube. At the small end of the tube is an electron emitter (called an electron gun); the inside of the large end is coated with phosphors. When electrons strike the phosphors, they glow, producing the dots we see. The paths of the electrons are controlled with electromagnets, which is why unshielded speakers or other magnets placed too close to a monitor can cause a variety of strange effects.

To create the array of dots we see, rather than the horizontal lines characteristic of a TV set, there is a mask between the electron gun and the inside front of the tube. There are two basic types of masks-one with round holes in it and one with rectangular slots. The distance between the holes in the mask determines the dot pitch.

A 0.28-mm dot pitch, for instance, means that each dot is 0.28 mm from the next one. Given that there are 25.4 mm to the inch, a 0.28-dot pitch represents about 91 dots per inch, while a 0.25-dot pitch increases the dots per inch to approximately 101.

Most monitor tubes come from a small number of suppliers-monitor manufacturers buy the tubes, then add their own electronics and cases. Thus, the differences between monitors from one manufacturer to another depend more on the design of the electronics, control mechanisms, and case design than on differences among tubes. For example, a very-high-quality tube installed in a monitor with inferior electronics will not look as good as a less-expensive tube teamed with good electronics.

How do you tell the difference? Price is not always a reliable indicator, although you do tend to get what you pay for-the market is too competitive for it to be otherwise. There are a number of technical qualifiers you can look for, such as resolutions of at least 1,024-by-768 pixels at 75 Hz on 15-inch monitors, 1,280-by-1,024 pixels at 75 Hz on 17-inch monitors, and 1,600-by-1,200 pixels at 75 Hz on 19- to 21-inch monitors. Also, as a general rule, the higher the maximum refresh rate at a given resolution, the better the quality of the electr onics in the monitor.

While some qualities such as maximum resolution, refresh rate, and dot pitch are easily quantifiable, it's harder to quantify other items that can make a big difference to someone trying to use the monitor for several hours a day. For instance, the consistency of focus from the center of the monitor to the corners and the evenness of brightness across the entire display are difficult to measure without specialized tools. However, the human eye is affected-monitors with uneven brightness or distorted lines may not appear at first glance to have problems, but can cause eye fatigue over time.

Another feature not easily quantified is antiglare technology. As concern grows for the quality of lighting in office environments and proponents of natural light are more often heard from, the modern, well-lit office environment is more hostile to displays. Lots of light is great for plants but it doesn't m ake reading monitors any easier. Antiglare coatings, etched tube surfaces, and flat or flat-square tubes can all help fight glare and reduce eyestrain.

Very Refreshing
Flicker is another well-known producer of eyestrain. One good test of a monitor is to display a screen that is predominantly white. This produces the maximum brightness and makes subtle variations in the output of light more visible. Higher refresh rates produce more stable whites, which results in less eyestrain.

The worst possible refresh rate is 60 Hz, because this is the frequency of electric lights. Tiny variations between the monitor's 60 Hz and the 60 Hz of the lights will produce a beat-the same sort of enhanced vibration that you can hear when two strings on a guitar are almost, but not quite, the same tone. With monitors, this beat frequency produces an easi- ly visible flick-er that often produces head-aches with extended use.

The current most popular style for word processors of black text on white background s makes the all-white background test quite relevant-a primary cause of eyestrain stems from the eye interpreting variations in brightness as movement on the display, and continuously changing its focus point as it tracks that perceived movement.

Warranties Count
Another critical monitor issue is the length of warranties. An inexpensive or remanufactured monitor may have a warranty as short as 30 days. Compared with the five-year warranties offered with many hard drives, this is a very short time, indeed. Even some expensive monitors come with only one-year warranties, or may have warranties of three years on parts, but less time on labor or the tube. Warranties are especially important because you are much more likely to need one on a monitor-or wish you had a longer one-than with any other piece of the computer. The best monitors have a three-year warranty on the tube, including parts and labor.

Because of the relatively high cost of monitors compared with other system components, and be cause SVGA (super video graphics array) has been the standard display mode for several years, it is much more common to see reconditioned monitors than other reconditioned parts. If you decide to try one, look for a model with a one-year warranty or better.

Get On The Bus
As monitor vendors try to differentiate their products, the features available on monitors continue to increase. Consider these features carefully to determine if they aid productivity. For example, given the number of business applications that use sound, integrated speakers and monitors are worthwhile features. It's less likely, however, that business users need a sub-woofer built into the base of their display.

Other features that business users may find more useful include on-screen adjustment of the display and Universal Serial Bus (USB) connectors. Most monitors allow both horizontal and vertical adjustment of the size and position of the screen image; many also allow the adjustment of rectangularity (also known as pincushion adjustment), which adjusts the sides of the display area to be parallel.

The method for accessing these controls varies widely, and individual preferences vary. Analog controls, which are not found much any more, feature small knobs for users to make adjustments. They have fallen out of favor because the settings may drift, making it difficult to maintain a well-adjusted display. Digital controls feature push buttons with a number of increments and may be labeled with a set of arrows for each adjustment. Another option is a selector button to choose which setting to adjust and a single set of arrow keys for making the adjustment. MAG InnoVision Co. Inc in Santa Ana, Calif., substitutes a knob for the arrow keys. Many people find knobs more intuitive and easier to control than the multiple presses required with arrow keys.

As USB becomes more widespread, monitors will provide standard USB hubs for connecting keyboards and mice to the monitor, instead of connecting each separately to the sys tem unit. USB connectors will also let the monitor communicate with the PC, allowing adjustments through control-panel software on the PC, instead of using the buttons or dials on the monitor.

Another, less-common feature that many users swear by is the pivoting display that can swivel from the usual landscape (horizontal) to a portrait (vertical) orientation. This is especially useful in word processing or graphic design. These displays were pioneered by Radius Inc. in Sunnyvale, Calif., for the Macintosh several years ago; the technology has since been licensed by Portrait Displays Inc., in Pleasanton, Calif.

Some other features that may be required of monitors used for graphics involve setting the color temperature and color accuracy of the display. Monitors do not produce a "pure" white, but one that has more or less blue in it. The amount of blue tint to a monitor's white is measured on the Kelvin temperature scale, which actually correlates the color with the surface temperature of a sun that wo uld produce the same color. A common setting is 6,500 degrees Kelvin, but other settings are used for specific purposes. The color temperature influences how all other colors appear on the screen as well, and is critical for graphic artists designing for a print medium.

Color-matching software and hardware, available from monitor manufacturers, allow a color sample to be replicated exactly on screen, making it easier to match colors without having to print out samples. It is also important to realize that the environment the monitor is in can greatly influence the colors displayed. For this reason, many art departments that use color-matching technology paint their rooms a neutral gray and use special lighting.

The vendors' drive to differentiate products and to give users a number of pricing options is producing a much greater variety of monitor sizes, which typically range from 14 inches to 21 inches, though some makers produce larger screens for presentations. Where many companies might once have h ad 14-, 17-, and 21-inch monitors, some product lines now also include 15-, 16-, 18-, 19-, and 20-inch models. The 18-inch monitors in particular are being heavily touted at the moment, because they offer a size advantage over the popular 17-inch models without being as expensive as the 19- to 21-inch monitors.

In the drive for bigger monitors, some companies are producing TV monitors in 27-inch, 31-inch, and larger sizes. Intended for both the home market and boardrooms, these monitors have both TV (NTSC) and SVGA inputs and can be used without converter boxes for both computer presentations and videos. Some companies are marketing these for consumers as a TV replacement that can also be used with a standard computer for Web surfing-an alternative to the WebTV.

Crystal Clear
Alternatives to the standard tube-based monitor include several types of dot-addressable displays, such as LCD (active and passive matrix) and plasma, as well as more exotic tube displays that have up to a million ele ctron guns in a single display. These displays are most often associated with portable computers but are starting to make headway in the desktop market. They offer high contrast and no distortion compared with tubes.

The downside to LCD displays is that they are noticeably slower in response time to full-motion video and quick movements on the display (though they are improving), and they cost much more than a picture tube of equivalent size.

The plus side of LCDs' slow response time is that the displays tend to be "persistent." The time for a pixel to return to the off state is longer than it takes to refresh it, which greatly reduces perceived flicker and thus may reduce eyestrain significantly. Also on the upside, LCDs lack the types of image distortion common to tubes, and also consume less power, weigh much less, and have a much smaller overall size for a given diagonal dimension compared with tubes.

The LCD display's lack of distortion stems from the fact that LCDs are addressed pixel by pix el, in a completely digital system. All the pixels are individually controlled, which eliminates the problems that monitor manufacturers face in making tubes that are consistent in geometry and illumination intensity. Tube monitors are actuated by a single beam of electrons moving across the display, which is controlled by analog circuitry. A picture tube is a compromise between the laws of physics and the best possible display, and can never be perfect.

LCD displays for desktops will continue to become more common and less expensive. The prevailing opinion is that the market for LCD monitors will really start to grow when their costs are reduced to two to three times the price of standard monitors. That time is rapidly approaching. Since a 16-inch LCD provides 16 inches of usable display, it is comparable to a 17-inch tube, which usually has only about 16 inches of usable area. A 17-inch tube generally costs between $700 and $1,000 today; Iiyama has a 16-inch LCD desktop display is currently available fo r $1,600.

Active matrix LCD displays for portable computers are clearly superior to passive matrix displays, but that difference is less clear in desktop units. With no power limitations and much less stringent depth requirements to constrain backlighting systems, desktop passive matrix LCD displays are quite readable and far less expensive than active matrix models. For example, a 17-inch passive matrix screen is available for half the cost of a 15-inch active matrix model. Passive matrix technology continues to improve, and passive models will probably become most prevalent on desktops.

The main reason LCD monitors are so much more expensive than tubes is that they are made by a process similar to the one used to make silicon chips. A display is made from a bottom layer, or substrate, with a large number of complicated processes that modify and add to the original layer. A problem in any part of the process ruins the display.

Where tubes might yield 80% or better of the tubes passing final insp ection, many LCD manufacturers would be very happy with a 50% pass rate. Active matrix LCDs are even harder to make than passive matrix displays, and more must be discarded during the manufacturing process.

Manufacturers continue to improve their technologies for getting better yields, and this, coupled with cost benefits from the increasing levels of production, will reduce prices. LCD monitors actually have the potential to become less expensive than tubes as manufacturing processes improve, although this is a long way off.

A Future In Plasma
Plasma displays offer the potential to provide the quick response times of tubes with all the other advantages of LCD displays.

Plasma displays operate on the same principle as neon tubes. A gas, usually xenon, fills the space between two sets of electrodes. It is excited when voltage is applied between the electrodes and generates ultraviolet light, which excites phosphors similar to the ones in monitor tubes, and produces visible light.

Ho wever, plasma displays are so new that they are still very expensive. Only time will tell if production yields and sales of large numbers of units will bring the costs down to a level where they will be widely adopted.

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