- Introduction
- Which LCD is right for me?
- LCD Basics
- Judging Image Quality
- Features and Connectivity Options
- Warranties
- Glossary
LCD basics
LCDs are no longer an item only the upper caste can afford. When shopping for an LCD, some specifications and features are more important than others. Here are a few of the biggies.
Aspect ratio: The standard proportion in width to height for a computer monitor is 4:3, but most new displays have a wider format: 16:9 or 16:10, designed for viewing movies or HDTV in wide format. Note that a 17-inch wide-format panel has about the same vertical dimension and vertical pixel count as a normal 15-inch panel, so you get about 120 percent of the viewing area of a 15-inch panel. A 17-inch standard panel, however, has 130 percent of the viewing area of a standard 15-inch screen.
Contrast ratio: A spec much hyped by manufacturers (be suspicious of their claims), this is the difference in light intensity between the brightest white and the deepest black.
Digital and analog connections: LCDs are digital devices and thus have to convert analog (VGA) signals before they can be displayed. A graphics card with a digital video interface (DVI) or high-definition multimedia interface (HDMI) can send the signal straight to the display in digital format -- no conversion required. At this point, most monitors do such a good job of signal conversion that digital connections are not as important as they used to be.
DVI connector.
VGA connector.
Luminance: Brightness: a measure of how much light a panel can produce. Luminance is expressed in either nits or candelas per square metre (cd/m²). A measurement of 200 to 250 nits is OK for most productivity tasks; 500 nits is better for TV and movies.
Pixel-response rate: This refers to how quickly a pixel can change colours, measured in milliseconds (ms); the lower the milliseconds, the faster the pixels can change, reducing the ghosting or streaking effect you might see in a moving or changing image. In general, manufacturers' specifications rely on best-case scenarios; real-world performance could be slower. A maximum response time of 12ms across the spectrum is required for gaming or viewing television and movies without ghosting or streaking. Manufacturers have debuted LCDs with response rates as fast as 2ms.
Portrait/Landscape modes: Some LCDs pivot so that the longer edge can go horizontal (landscape mode) or vertical (portrait mode). This feature can be useful for desktop publishing, Web surfing, and viewing large spreadsheets, but don't pay extra for it if you won't use it.
Portrait mode.
Landscape mode.
Resolution: Make sure you are comfortable with an LCD's native resolution before you buy it. Remember, an LCD that scales its image to a non-native resolution will never look as good.
Viewing angle: The physical structure of LCD pixels can cause the brightness and even the color of images to shift if you view them from an angle rather than facing the screen directly. Take manufacturer's specifications with a grain of salt and make your own observations if possible; viewing-angle issues become more critical as panel size increases.
CRT Basics
You can get a lot for your money with CRTs, although they're often much bigger and heavier than LCDs. In recent years, CRT technology has advanced, so there is very little difference in performance among brands. In other words, unless you buy the absolute cheapest CRT, you should be happy with whatever you choose. Here are some key features in CRT specifications.
Bandwidth: The rate in megahertz (MHz) at which a CRT can process information. As you approach the bandwidth limit, thin black or white lines appear gray because the electron beams cannot turn all the way on or off fast enough to keep up. Generally, the higher a CRT's bandwidth is, the faster its refresh rate is at any resolution, and the better its image quality.
Convergence: Colour CRTs rely on three separate electrical beams to project simultaneous red, green, and blue images; these combine to form a full-colour image. If these beams are not precisely aligned, the red, green, and blue portions of the image may not overlap correctly; the image will look unfocused and will have visible colours along the edges. When the three beams converge correctly at all points on the display, you get a perfect image.
Illustration of horizontal dot pitch.
Dot pitch: A smaller dot pitch means that a monitor can display higher-resolution images more accurately. Some manufacturers report the "horizontal dot pitch," which measures only the horizontal component of the diagonal distance between triads and offers an easier comparison to stripe-pitch measurements.
Maximum refresh rate: If an image refreshes too slowly on a CRT, you may notice a flicker. You want at least 70Hz at the resolution you intend to use. This becomes more of a factor as the screen size gets larger, as people are more susceptible to flicker in their peripheral vision.
Power consumption: CRT power consumption is typically specified in watts. A typical 19-inch model may draw 130 watts when operating -- that's more than two standard 60 watt lightbulbs and will generate a good deal of heat.
Screen size: CRTs specify the diagonal dimension of the entire picture tube. This is one to two inches larger than the viewable image size (also measured diagonally).
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27/03/2008 04:25 AM
my question was ......digetal vs. analogue computer monitor?
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