3 September 2003

Cathode Ray Tube (CRT) monitors suffer more than their share of misleading specifications. The good news is that if you're not picky, virtually any monitor on the market today will provide a stable, acceptable image for most applications. If you're hard to please, beware, because it's easy to get obsessive over tiny differences in image quality.

Before we do the numbers, let's consider more important aspects, like the choice of CRT type. The Sony Trinitron CRT (Mitsubishi licenses this technology under the Diamondtron brand) uses a fundamentally different technology - an aperture grille - and costs a little more than most other CRTs. Colours, particularly reds, tend to be slightly richer and the screen a bit brighter, but tiny text may be a little less crisp. On the other hand, the two hairlines that are visible near the top and bottom of the screen can be distracting to sensitive eyes. For this basic decision -Trinitron or not? - look for yourself, and if the two horizontal lines bother you, then you will want to look for a shadow mask CRT.

Another crucial non-numeric issue is the shape of the screen. You might consider paying extra for a so-called flat-flat or true-flat CRT. A flat screen drastically cuts glare, the enemy of comfortable viewing. Flat-square CRTs actually have a slight curvature, but they're often brighter and slightly sharper around the edges of the screen than perfectly flat screens. Again, let your eyes be the judge.

Now, the numbers. Remember the old cliché, "Lies, damn lies, and statistics"? Keep it in mind as you ponder the monitor specifications that salesmen throw at you.

Higher resolution means sharper images, right? True, but at maximum resolution, most CRT monitors shrink Windows text, buttons, and bars to the point where they're too small to view or click comfortably, and the refresh rate may slip to the point where flicker becomes irritating. The following table shows the optimum resolutions for three popular monitor sizes (measured in inches diagonally).

Size Resolution
17" 1024x 768
19" 1280x1024
21" 1600x1200

Any monitor worth considering should be able to produce these resolutions at a refresh rate of 75Hz or higher, which these days includes nearly every monitor sold. So, for most of us, more is just wasted capacity and expense. Only CAD/CAE users and graphic artists really need exceptionally crisp, fine lines.

Dot pitch
Display Mate Technologies which develops the leading monitor-testing software, refers to dot- pitch promotion as "the great dot-pitch swindle". Dot pitch, measured in fractions of a millimetre - typically from 0.20 to 0.28mm - most commonly refers to the distance between any two dots of the same colour (triads of red, green, and blue phosphor dots make up the pixels that form a CRT image). Theoretically, smaller dot pitches mean crisper images. But vagaries in how manufacturers measure dot pitch mean you can't rely on this number for CRT comparisons. The rule of thumb: avoid 17-inch monitors coarser than 0.28mm and 19-inch monitors coarser than 0.26mm. Graphics professionals should consider a CRT with a 0.20mm or 0.22mm dot pitch. This indicates a CRT that uses Enhanced Dot Pitch technology, which produces exceptionally clean vertical lines.

Viewable screen area
The viewable area of CRT monitors measures slightly smaller than the advertised diagonal CRT size. A 19-inch CRT, for example, generally gives you an 18-inch screen area (because the measurement includes the plastic casing around the outside of the screen, called a bezel, or frame). Check this number carefully; some monitors vary by as much as an inch and a half.

Horizontal scanning frequency
This key number, measured in Kilohertz (KHz), indicates how high you can push the refresh rate at any resolution. Some people are sensitive to flicker, so watch the horizontal scanning frequency. If you crave a rock-solid image, an 85Hz refresh rate should be enough for anyone.

In rare cases, a monitor won't run at an 85Hz refresh rate even if the horizontal scanning frequency is high enough to support it. The moral: if you care about higher-than-normal refresh rates, double-check the specifications to make sure that the manufacturer explicitly supports the refresh rate you want at the resolution you'll be using. The vertical scan frequency that is always listed next to the horizontal scan frequency range? Vertical scan frequency is just another way of saying refresh rate.

Here are the horizontal scan rates necessary to achieve 85Hz at the following resolutions:
Size Scan rate
1024x 768 70 KHz
1280x1024 96 KHz
1600x1200 110 KHz

A flicker-free 85 Hz refresh requires an increasingly faster horizontal scan as the resolution increases.

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