Response time: the faster, the better?

If you've been shopping for a monitor in recent months, you may have noticed a lot of attention being given to one spec in particular: response time. Also referred to as response rate or latency, an LCD's response time supposedly indicates how fast it can display moving images. Most of last year's LCDs came with 16-millisecond (ms) response times--fast enough for decent-looking DVD playback, though with some ghosting and distortion. But response times are falling, and with Samsung and ViewSonic debuting LCDs with 3ms and 4ms response times earlier this year, LCDs would appear to be nearing the performance offered by CRTs. But what do response time numbers really mean?

A faster response time is better--it indicates how quickly the screen can refresh a video image. If an LCD's response time is too slow, the display's pixels won't be able to keep up with the information sent from the computer's graphics card, and you'll see ghosting and digital noise as a result. But just because a vendor advertises a fast response time doesn't mean that its LCD will handle moving images better.

Response time is defined as the time required for an LCD pixel to change from fully active (black) to fully inactive (white), then back to fully active again. Many manufacturers, on the other hand, report their LCDs' gray-to-gray response times. Pixels are rarely completely on or off--instead they cycle between gray states, that is colors--and, in general, switching between gray states is much slower than switching between black and white. However, some also argue that measuring gray-to-gray response time is pointless, since the manufacturers rarely tell where in the cycle they start and end their measurements. To alleviate this confusion, the Video Electronics Standards Association (VESA) plans to introduce a spec standardizing response time measurement sometime in 2006.

In the present, however, manufacturers still report the "fastest possible" response time, instead of the average or typical response time that you and I would see in daily use. And, sometimes manufacturers can't even decide how fast their own products are, as with ViewSonic's September 2005 announcement that its ViewSonic VX924 LCD actually had a 3ms response rate rather than the previously announced 4ms rate.

In any case, while response time specs may help when looking for a monitor for viewing DVDs or playing video games, we recommend testing a monitor yourself before buying. CNET does not officially test response times, but we judge gaming and DVD performance with our own eyes, and we urge you to do the same.

Here are a few monitors we've tested with relatively fast response times of 8ms or less. Their performance on DVD and gaming tests varied greatly.

ViewSonic VX924 Samsung SyncMaster 915N BenQ FP91E

BenQ FP72G+S LG Flatron L1981Q

More resources:

LCD monitors for gamers LCD connections: analog vs. digital Editors' top monitors CRT vs. LCD monitors