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Video Display Monitor Technology 2001
by By Herbert Wong, Jr., NOCCC Hardware SIG Leader, ocug@SingularityTechnology.com - April 17, 2001 at 14:58:19:
The video monitor is arguably the most important and most frequently used computer component. It is therefore surprising that most users so casually pick a monitor for their computer system. The selection of a high quality monitor can bring substantial health benefits and increase productivity for pennies per hour.While you read text and graphics, the video monitor is the key component while most other components sit by idly. Certainly no other component can so quickly cause physical distress, such as eyestrain and headaches.
A display is the hardware component that physically shows the video output. The most common display technologies are CRT (cathode ray tube), LCD (liquid crystal display), and plasma (a topic for the future). A monitor contains a combination of a display and the associated electronics required to convert the source video signal into a format that is suitable for use by the display.
CRT—A cathode ray tube is a display technology that uses electron beams to stimulate phosphors so they emit light. This part of the technology is not that important to the average user.
The CRT’s electron guns (usually three, sometimes one or two depending upon the design) emit a stream of electron beams (plus spurious radiation) that are directed magnetically by a yoke. The electrons strike phosphors on the front glass of the CRT.
The phosphors are organized as pixels (picture elements). The pixels are usually three round dots in a triangle called a triad. The triad has one red, one green, and one blue (RGB) phosphor.
A perforated metal sheet, the shadow mask, is placed near the glass inside the CRT. An electron beam is supposed to go through a perforation and exactly strike a specific phosphor (red, green, or blue). This is not practical, so the beam is made larger than necessary. The shadow mask absorbs the overage and the perforation permits the beam to pass through to the phosphor.
The shadow mask heats up and must have a low coefficient of expansion so that the correct phosphors are always correctly illuminated. Invar is a suitable material that frequently appears in advertising material.
Let’s recap this. Each electron gun emits an electron beam. The yoke magnetically directs the beam through a perforation in the shadow mask. The beam hits a specific phosphor that is “painted” on the glass. The phosphor emits photons (light). The light passes through the glass to the eyeball of the viewer.
Flat versus Flat—CRTs were historically made so that the front display surface was a section of a sphere. Hence, the display was curved in all directions. Later, so-called “flat” screens were created from sections of a much large sphere. The resulting display surface was less noticeably curved, but they were still not absolutely flat.
Sony’s original Trinitron CRT technology is vertically flat. The display is created from a section of very large cylinder. As a result, incidental room lighting can be better controlled.
Today, absolutely flat displays are becoming common. The display surface is flat in all directions.
Aperture Grill versus Shadow Mask— Shadow masks are sheets of metal that typically have round holes in them. The size of the phosphor is restricted by the technology.
Aperture grills were created to improve upon the technology. An aperture grill is composed of many (sometimes over two thousand) fine wires aligned vertically next to the glass. The phosphors are now stripes of red, green, or blue. The aperture grill is used in place of the shadow mask. The resulting stripes of phosphors can potentially be brighter than standard shadow mask technology.
The most common implementation of aperture grill technology is the Sony Trinitron tube. Its other features include a single electron gun instead of three (to theoretically improve electron beam aim) and a vertically flat CRT.
LCD—Liquid crystal diode (LCD) technology is totally different from CRT technology. LCD panels allow light to pass through them, CRTs emit light.
A polarizing filter blocks light waves from passing through it except, for example, horizontally oriented light waves. Two stacked (sandwiched) “horizontal” polarizing filters allow the horizontal light waves to pass through them.
If one of the “horizontal” polarizing filters is rotated ninety degrees (to become a “vertical” polarizing filter), no light will pass through. What happened? First, the “horizontal” polarizing filter only allows “horizontal” light waves through. Second, the “vertical” polarizing filter will only allow “vertical” light waves through. After the first filtration, there are only “horizontal” light waves remaining and those are likewise blocked.
Now, suppose you could selectively place conduits between the “horizontal” and “vertical” polarizing filter stack. These conduits could, at will, rotate (by ninety degrees) the transmitted “horizontal” light waves. The light waves now appear to be “vertical” light waves and they are transmitted! When the orientation of the “conduit” is changed, the light is no longer correctly oriented and nothing is transmitted.
This is how LCD panel technology works. The liquid crystals are the conduits that change when an electrical signal is applied.
A variation to the LCD involves the use of transistors in place of the passive liquid crystals. These active matrix displays can be much faster to reorient, permitting superior dynamic images.
LCD technology can potentially offer much greater contrast ratios than CRT technology. Since there are no electron guns or magnetic yokes, there is significantly less radiation from an LCD panel, and, power consumption can be a fraction of a CRT.
LCD panels are best used at the specified resolution (for example 1024x768 at 60 hertz). If such a display is used at 800x600, the displayed image could have a 112 pixel black border on the two sides and 84 pixels on the top and bottom. Or else, the image would be awkwardly stretched to fit display.
LCD displays don’t need to be refreshed (see Refresh Rates below) liked CRTs. The LCD “conduit” removes this need. Therefore, LCD displays should be refreshed at their “natural” electronic rate of 60 hertz instead of 72 hertz or higher.
Resolution—Resolution of a monitor refers to the way the image is created. Think of your video monitor’s image as a piece of graph paper. Each cell of the graph is a pixel (picture element) that has a red, green, and blue (RGB) component.
A monitor might have a resolution of 800x600. That would be a graph paper with 800 cells wide and 600 cells high. Suppose the graph paper has one hundred cells per inch. The display would be eight inches wide and six inches high.
A second monitor has a diagonal that is twice as long and therefore double the width (sixteen inches) and double the height (twelve inches); and, thus, four times the surface area. If we retained the same 800x600 resolution, the graph paper would have to be stretched to fit. The image is now twice as big! Each cell of the graph paper is now stretched to fifty cells per inch. This change is good for the visually impaired.
Let’s try it another way. If we applied the same one hundred cells per inch graph paper to the display, we could then view four such pages. In other words, we now have a resolution of 1600x1200 and the image would still be the same size. Only now, we could simultaneously display four such images! More information at one time!
Most monitors support common resolutions of 640x480, 800x600, 1024x768, 1280x1024, 1600x1200, 2048x1536, etc.
Refresh Rates—The human eye has a natural image retention time. Computer display images are dynamic and must be periodically refreshed. The interaction between the human eye, room lighting, and the CRT display can cause unwanted side effects like flicker which results in eye strain.
It is best to set the horizontal refresh rates to much higher than 60 hertz to avoid interaction with fluorescent lighting. The minimum recommended horizontal refresh rate for small CRT monitors is 75 hertz. Larger monitors may require a minimum of 85 hertz. This is because flicker is more pronounced in the peripheral vision (which is bigger on larger displays).
Of course, higher refresh rates require more expensive electronics. Try finding a monitor that will support 2048x1536 at 85 hertz! However, you should spend more money and get a higher bandwidth monitor than you will use. If you run your monitor at the maximum resolution and maximum refresh rates, it will likely shorten its lifespan. A more capable monitor will jog along whereas a less capable monitor will sprint to a fiery end.
What you see is—The size of a computer video monitor is specified as a diagonal measurement, in inches (in the United States), of the display. This is not a simple as it appears and it has been a problem for about three decades (which is forever in the personal computer world).
When a monitor is constructed, it usually has a protective bezel that surrounds the four sides of the display like a frame around a picture. Part of the display is hidden beneath the bezel. Obviously, the portion of the display that is behind by the bezel is not visible and therefore is unusable.
Manufacturers classify monitors according to the diagonal size of the entire CRT, including the portion hidden by the bezel. Since the bezel can be designed to obscure any arbitrary amount of the display, knowledgeable computer users measure the visible diagonal from the inside of the bezel corners. Manufacturers, fearing that their deceitful specifications would engender excessive consumer scorn, ultimately specify both the monitor’s class (ex. 17-inch CRT) and visible diagonal (ex. 15.1-inches).
To further complicate matters, LCD monitors usually don’t hide usable portions of the display. Therefore, the total physical diagonal of an LCD monitor is the same as the visible diagonal. In practical terms, a 15-inch LCD monitor has almost the same usable size as a 17-inch class CRT monitor.
Overscan describes the image on the display that is hidden by the bezel. This is the common condition of an NTSC television image. If you carefully watch the left edge of your television broadcasts, you can sometimes see words that are missing the first character or two. The missing characters are actually displayed behind the bezel. A true television monitor does not have overscan; the whole image is visible so that editors know exactly what is being shown.
Overscan is an unacceptable condition for a computer image. A computer image must be adjusted to place it within the visible area inside the bezel.
The viewable area of a CRT display is calculated by elementary geometry. Viewable area equals the viewable height times the viewable width. Typically, only the viewable diagonal is known. The standard monitor’s width to height ratio is 4:3. Applying a little Pythagorean algebra allows the viewable area to be calculated from the visible diagonal.
For simplicity’s sake, we’ll assume that 1.5 inches of the physical display is hidden by the bezel in a CRT monitor. The viewable area of a CRT monitor with a physical diagonal of 14 inches (12.5 inches visible diagonal) is 75 square inches, 15 inches (13.5 inches visible diagonal) is 87.5 square inches, 17 inches (15.5 inches visible diagonal) is 115 square inches, 19 inches (17.5 inches visible diagonal) is 147 square inches, 21 inches (19.5 inches visible diagonal) is 182.5 square inches, etc.
A 17-inch class CRT based monitor has about one-third more visible area than a 15-inch class CRT based monitor. A 19-inch class CRT has two-thirds more area than a 15-inch class. A 21-inch class CRT has over twice the area of a 15-inch class CRT.
Likewise, a 19-inch class CRT based monitor has about one-quarter more visible area than a 17-inch class CRT based monitor. A 21-inch class CRT has over one-half more area than a 17-inch class.
Bear in mind that the CRT’s volume increases geometrically as it increase in size. The CRT’s very large glass container gets very thick and heavy to support the large vacuum inside. As a result, manufacturing and shipping costs increase dramatically and transportation becomes problematic. A 19-inch class CRT in its shipping carton won’t fit inside most sedans. Even 17-inch CRT monitor boxes are inconvenient to bring back from the store.
A case in point is a 19-inch class CRT monitor that I have been looking at. It has about 147 square inches of screen area. The 21/22-inch class electronic equivalent of this monitor has about 25-38 percent more screen area. The prices are about $525 and $950, respectively. That’s about 80 percent more expensive.
What you get—Computer monitors have several basic controls to adjust the image. These include size and position controls for both horizontal and vertical image, brightness, and contrast. More extensive controls are built into more expensive monitors.
For ease of explanation, let’s consider a monitor that has a visible area within the bezel that is eight inches wide and six inches high. When the computer is connected, the monitor usually needs to be adjusted for that video card’s signal (for each given resolution; which can be changed through the Windows Control Panel Display icon’s Settings tab).
In our example, the image (of the Windows desktop) should be eight inches wide and six inches tall and fit perfectly within the borders of the bezel. Most likely, it will require some adjustment to properly configure it. This is a trial and error process and may take a minute or two to do for the first time.
I find that it is easier to first adjust the image size so that it is obviously smaller than the visible display area using the horizontal size and vertical size controls. Then, use the horizontal position and vertical position controls to center the image within the visible display area. Once again, use the size controls to increase the image size to the required eight inches wide and six inches high. Reposition and resize as needed.
The contrast control adjusts the ratio between the brightest white and darkest black. This helps configure the visibility of the gradients of different shades of color.
The brightness control sets the maximum illumination (brightness) of the image.
The inclusions of other controls are usually all devote to improving imperfections in the image. They might be trapezoidal, pincushion, barrel, moiré pattern, etc.
Plug-And-Play—Plug-And-Play support allows a monitor to report its specifications and manufacturer’s information to Windows to use in its configuration. Video display adapters typically have higher performance capabilities than video monitors. It is important to use a video signal with a resolution and refresh rate within the capabilities of the monitor. Excessively high frequencies can shorten the life of the monitor or even cause immediate damage.
Plug-And-Play will allow Windows to include only settings (in the Windows Control Panel Display icon’s Settings tab) that are mutually compatible between the video adapter and monitor.
If the video resolution cannot be changed from the Windows Control Panel/Display/Settings tab, it is possible that the monitor hasn’t been configured properly by Plug and Play. By clicking on the Advanced button (your version of Windows probably is different).
USB—USB support is usually limited to having either a passive or a powered USB hub in the base (stand) of the monitor. It can also be a convenient location to plug-in USB devices. A powered hub can supply sufficient power for most USB devices, but check the manufacturer’s documentation to be safe. Unfortunately, the USB option is far more expensive than buying a small third party USB hub for $20-40.
More elaborate USB support can allow you to configure the monitor’s settings by using the Windows interface (including keyboard and mouse). I am not sure that I can see the advantages of this, other than it might ultimately be less expensive to build and support instead of having additional controls on the monitor’s case. There are the usual problems with having any USB device (that is something will go wrong sometime).
Electromagnetic Emissions—New and more expensive monitors comply with various electrical and magnetic field emissions standards. The European emissions standards are more rigorous than American standards.
The Swedish Government standards, referred to as MPR-I and MRP-II, are commonly cited. They limit extremely low-frequency (ELF) and very low-frequency (VLF) emissions. The more stringent Swedish Workers Union (Tjanstemannens Central Organization) TCO-92 and TCO-95 standards limit emissions from the front of the monitor in addition to adding energy conserving features.
As a general rule, the front of monitor has lowest emissions. The sides and back of the monitor emit the most. It is suggested that long term exposer be no closer than at least three feet from a CRT monitor.
LCD panels have almost no emissions. Plasma monitors may also be similar.
New research may contradict the prior concerns about the dangers of electromagnetic radiation. It is not the point of this article to address this topic. However, a starting point would be the following articles: “Should I be concerned about monitor emissions?” (http://www.monitorworld.com/faq_pages/q14_page.html) and “What’s the Problem?” (http://www.eaie.nl/activities/es/ENIS/HEALTH/problem.html).
Energy Saving—Now that we’re facing a new energy crisis it is important to know that monitors have various levels of power management for energy savings. The features vary by manufacturer.
VESA Display Power Management Signaling (DPMS) was an early standard. It allowed a DPMS compliant video card and monitor to use the horizontal synchronization (H-sync) and vertical synchronization (V-sync) lines to implement different levels of energy consumption. For CRT based monitors DPMS functions can save considerable amounts of power compared to leaving the monitor in normal display mode.
Normal operation uses the maximum power, of course. This is typically about 100 to 150 watts depending upon the monitor’s size.
Standby mode shuts off the CRT’s RGB guns, the power supply remains on, and the tube filaments remain energized. This is usually the elementary screen saver mode. Power consumption is less than 110 watts. Normal operation can resume in two to three seconds.
Suspend mode shuts off the CRT’s RGB guns, the power supply is shut off, and the tube filaments remain energized. Power consumption is less than fifteen watts. Normal operation can resume in two to three seconds.
Power off mode isn’t power off. A small amount of power is consumed by a circuit that monitors the H-sync and V-sync signals. It will resume normal operation through software (operating system) and hardware control. Power consumption is less than five watts. Normal operation can resume in eight to ten seconds.
If the monitor is not going to be used for long periods of time and energy conservation is important, there is only one solution. The monitor must be disconnected from the power mains circuit. It can either be unplugged or put on a power strip that is shut off. In theory, this should save about 120 watts per day (about one-eighth of a kilowatt-hour).
Newer USA Environmental Protection Agency (EPA) Energy Star (http://yosemite1.epa.gov/estar/consumers.nsf/content/monitor.htm) compliant monitors can be configured to automatically enter power saving modes. It can be used in conjunction with operating system support for power saving modes.
Conclusions—I firmly believe that you should get the best monitor that you can for your application. A superior quality monitor will last for two or three generations of your computer systems. A good monitor is good for your physical health because it can reduce eyestrain, headaches, body stresses, etc.
A $1,000 monitor that is used for eight hours per day, five days per week, and fifty weeks per year (2000 hours per year) that lasts for five years costs only ten cents per hour to own (not including electricity).
LCD panels are becoming attractively priced. They free up lot so desk space and can be positioned anywhere on a desk, even where they are meant to be! Just remember to use the LCD panel at the recommended resolution. Test it with your application. I have heard horror stories of mass installations before testing was done.
For now, I want an extra large CRT monitor running at high resolutions with ultra high bandwidth electronics. Make that two monitors so I can try multiple monitor support in Windows…
Resources—IBM Information Brief “Finding the Perfect Match – Choosing the Right Monitor” (http://www.pc.ibm.com/us/infobrf/ibmon.html).
The PC Guide Monitors (http://www.pcguide.com/ref/crt/index.htm).
Computer Shopper “Choosing a 15- or 17-inch Monitor” (http://www.zdnet.com/computershopper/edit/cshopper/shopguid/0695/).
Philips (Pakistan) Monitor FAQ (http://www.philips.com.pk/ce/data/monfaq.htm) and, some, TCO definitions at http://www.philips.com.pk/ce/data/term-e.htm.
U.S. Environmental Protection Agency (EPA) Monitors (http://yosemite1.epa.gov/estar/consumers.nsf/content/monitor.htm).
Contacts—This article first appeared in the North Orange County Computer Club’s (http://www.noccc.org/) Orange Bytes for May 2001. The latest version can be found at http://www.SingularityTechnology.com/articles/videomonitortech2001.html.
You can contact me, Herbert Wong, Jr., at ocug@SingularityTechnology.com
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