Faster-Responding Displays Not Just For Gamers

While typical business users are not likely to toss out older displays for faster models, gamers will surely see the difference. And to some degree, all users will benefit.

What is response time? The measurement is derived from a pixel's rise time plus fall time; rise time is how long it takes a pixel to go from off to on and fall time is the opposite. Specifically, an LCD's rise time refers to a pixel's ability to change from 10 percent color to 90 percent color, while fall time refers to the change from 90 percent color back to 10 percent. Put simply, it is a measure of how long it takes a pixel to change colors.

An old-fashioned CRT's response time is that of the phosphor itself, and it's measured in nanoseconds. An LCD response time, however, is measured in milliseconds. That hardly seems a fair contest. LCDs have a long way to go before they are as responsive as CRTs, and CRTs will continue to be favored for demanding applications such as gaming. Graphics artists also favor a CRT's ability to render color accurately.

But LCDs have other advantages. CRTs require that the pixels be reset on every refresh scan or they black out, and that's why they can flicker. In contrast, LCD displays don't refresh--the pixels stay set until they are made to change so there is no flickering.

Despite the lack of flicker, LCDs still have relatively slow response times. If that delay is too long, they can't keep up with changes to the input signal, and the net effect is the blurring and ghosting of the image.

Some manufacturers talk about "gray-to-gray" performance rather than rise-fall response time. ViewSonic, Walnut, Calif., is touting a display, which is slated to be out by June, that boasts a 4ms gray-to-gray response time.

What does this mean? A gray-to-gray specification refers to how fast a pixel can change from one shade to another shade of the same color. A gray-to-gray specification is perhaps more important than rise-fall time for video and gaming applications because the motion in video and gaming consists mainly of small changes in brightness and shades of the same color, with fewer rapid changes from one color to another.

On the other hand, rise-fall response time is more important for the display of scrolling text, for example, where pixels must change abruptly from one color to another. Another reason why users running everyday productivity applications will benefit from more responsive displays is that a flat panel's viewing angle is directly related to response time.

If you think of an LCD pixel as a light valve, or flashlight, it makes sense that when you look at it head- on it will appear at its brightest. The same is true for color. The sooner a pixel appears and the longer it stays in place, the more time the eye has to see the image and the intended color. Eye fatigue can result when color and brightness are not at optimum levels or not consistent across all parts of the screen.

Viewing angle is often associated with how easy it is for a group of people to look at the same display, but it is also important for a user sitting directly in front of the display.

When a display is set up so that a user is looking directly at its center, the user has to look up, down and side to side to see other parts of the screen, which are then viewed at an angle. The net effect, especially with displays 19 inches and larger, is that from the user's point of view, brightness and color will vary across different parts of the screen. And that leads to eye fatigue. So in a nutshell, the faster a display's response time, the less eye fatigue users will experience.

Samsung, NEC and ViewSonic are among the vendors touting 8ms displays priced in the $400 to $500 range. Soon they will become last year's models.

The new, faster LCD displays will be welcomed by business users already upgrading from CRTs. The promise of less eye fatigue, wider viewing angles, faster scrolling and better handling of video should be enough to convince many to pay the slight premium.