Video Hardware, Part 2 - Emissions
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Another trend in green monitor design is to minimize the user's exposure to potentially harmful electromagnetic fields. Several medical studies indicate that these electromagnetic emissions can cause health problems, such as miscarriages, birth defects, and cancer. The risk might be low, but if you spend a third of your day (or more) in front of a computer monitor, that risk is increased.
The concern is that VLF (very low frequency) and ELF (extremely low frequency) emissions might affect the body. These two emissions come in two forms: electric and magnetic. Some research indicates that ELF magnetic emissions are more threatening than VLF emissions because they interact with the natural electric activity of body cells. Monitors are not the only culprits; significant ELF emissions also come from electric blankets and power lines.
Note -ELF and VLF are a form of electromagnetic radiation; they consist of radio frequencies below those used for normal radio broadcasting.
The standards shown in Table 15.5 have been established to regulate emissions and other aspects of monitor operations. Even though these standards originated with Swedish organizations, they are recognized and supported throughout the world.
Table 15.5 Monitor Emissions Standards Standard Name | Established by | Date Established | Regulates | Notes |
MPR I | SWEDAC 1 | 1987 | Monitor emissions | Replaced by MPR II |
MPR II | SWEDAC 1 | 1990 | Monitor emissions | Added maximums for ELF and VLF; minimum standard in recent monitors |
TCO 2 | TCO 2 | 1992, 1995, 1999, 2003 | | Tighter monitor emissions limits than MPR- II; power management TCO '95, '99, and '03 add other classes of devices to the TCO standard |
1. The Swedish Board for Accreditation and Conformity Assessment
2. Swedish abbreviation for the Swedish Confederation of Professional Employees
Today, virtually all monitors on the market support TCO standards.
If you aren't using a low-emission monitor yet, you can take other steps to protect yourself. The most important is to stay at arm's length (about 28 inches) from the front of your monitor. When you move a couple of feet away, ELF magnetic emission levels usually drop to those of a typical office with fluorescent lights. Likewise, monitor emissions are weakest at the front of a monitor, so stay at least 3 feet from the sides and backs of nearby monitors and 5 feet from any photocopiers, which are also strong sources of ELF.
Electromagnetic emissions should not be your only concern; you also should be concerned about screen glare. In fact, some of the antiglare panels that fit in front of a monitor screen not only reduce eyestrain, but also cut ELF and VLF emissions.
Note that because plasma and LCD panels don't use electron guns or magnets, they don't produce ELF emissions.
Frequencies One essential buying decision is to choose a monitor that works with your selected video adapter. Today, virtually all monitors are multiple-frequency (also called multiscanning and multifrequency) units that accommodate a range of standards, including those that are not yet standardized. However, big differences exist in how well various monitors cope with various video adapters.
Tip -High-quality monitors retain their value longer than most other computer components. Although it's common for a newer, faster processor to come out right after you have purchased your computer or to find the same model with a bigger hard disk for the same money, a good quality monitor should outlast your computer. If you purchase a unit with the expectation that your own personal requirements will grow over the years, you might be able to save money on your next system by reusing your old monitor.
Some useful features include the following:
Front-mounted digital controls that can memorize screen settings
Onscreen programmability to enable you to precisely set desired values for screen size and position
Self-test mode, which displays a picture even when your monitor is not receiving a signal from the computer
With multiple-frequency CRT monitors, you must match the range of horizontal and vertical frequencies the monitor accepts with those generated by your video adapter. The wider the range of signals, the more expensive—and more versatile—the monitor. Your video adapter's vertical and horizontal frequencies must fall within the ranges your monitor supports. The vertical frequency (or refresh/frame rate) determines the stability of your image (the higher the vertical frequency, the better). Typical vertical frequencies range from 50Hz to 160Hz, but multiple-frequency monitors support different vertical frequencies at different resolutions. You might find that a bargain monitor has a respectable 120Hz vertical frequency at 640x480 but drops to a less desirable 66Hz at 1280x1024. The horizontal frequency (or line rate) typically ranges from 31.5KHz to 90KHz or more. By default, most video adapters use a 60Hz default vertical scan frequency to avoid monitor damage.
Although LCD monitors use lower vertical frequencies than CRTs, they avoid problems with screen flicker because of their design. Because they use transistors to activate all the pixels in the image at once, as opposed to a scanning electron beam that must work its way from the top to the bottom of the screen to create an image, LCD panels never flicker.
 | This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today. Buy this book now! |
Next: Refresh Rates (Vertical Scan Frequency) >>
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