Response Time, Input Lag, And Final Words
|Brand||Panel||Response TimeFull Black-to-White|
|Dell SR2220L||TN||16 ms|
|LG E2241V||TN||17 ms|
|Samsung S22A350H||TN||18 ms|
|Acer GD235HZ||TN||16 ms|
|Dell U2711||H-IPS||23 ms|
|NEC PA271W||H-IPS||20 ms|
We explored response time measurements in our 22" LCD roundup, but those monitors were all TN-based. IPS is a completely different technology. Moreover, today's Larger monitors employ a more evolved form of the technology called H-IPS, which improves contrast ratios and allows for more natural white production. Despite the fact that they're newer than what we saw five year ago, their response times are still typically slower than what we see from TN-based LCDs.
Benchmarking that lag with a camera is the fastest way to measure performance. Of course, normal cameras won't cut it, since they only shoot at 29 FPS. That's unacceptable if you're trying to measure precise time differences. Going the stop-watch route is no better due to human-introduced errors. That's why we're using a 1000 FPS high-speed camera to measure the time between clicking the mouse and getting a muzzle flash in Call of Duty: Modern Warfare 2. Since, one frame is equal to one millisecond, it’s possible to measure timing with a high degree of accuracy.
Granted, there are issues with this approach. When you disable vertical sync in a game, you're letting the game engine render at a rate different than that of the LCD. However, that doesn't change the refresh rate inherent to a monitor. Most LCDs, including the ones we're testing today, refresh at 60 Hz, which means that there can be up to a 34 ms variance between benchmark trials on the same monitor. The problem is that there's no way to ensure that two LCDs are operating on the same refresh cycle. It's possible that the frame with a muzzle flash might get kicked over to the next screen refresh for one monitor, whereas it wasn't there on another. That's why we took the average of five input lag measurements.
|Brand||Panel||Response TimeFull Black-to-White||Total Input Lag|
|Acer GD235HZ||TN||16 ms||73 ms|
|Dell U2711||H-IPS||23 ms||98 ms|
|DoubleSight DS-277W||H-IPS||21 ms||82 ms|
|NEC PA271W||H-IPS||20 ms||115 ms|
Arguably, this isn't a pure input lag test. It's more akin to the responsiveness you'd see while gaming, because it includes the time for the computer to process your movement. However, that idea of "total input lag" is what's really important, as it ultimately affects your reaction time. According to research published by Clemson University, the average college student has a reaction time of 200 milliseconds to visual stimuli, but if you're a truly competitive gamer, you'll likely end up under 100 ms. What's your reaction time? Test yourself.
If you possess superior gaming abilities, there are some differences between these three models. NEC's PA271W has a slightly more lag due to hardware circuity that's preprocessing color information. Interestingly, DoubleSight's DS-277W does relatively well. Meanwhile, Dell's U2711 operates in the middle of the road, just under 100 ms. The broader point here is that, fortunately, input lag is becoming less of an issue on the latest IPS-based LCDs. If you don't fall into that group of gamers, there's very little to worry about. Clearly, today's H-IPS panels offer better performance than yesterday's S-IPS based LCDs.
What monitors do you want to see us review next? Tell us below in the comments section! A special thanks goes to Accell Cables who sent over an UltraAV DisplayPort to DVI Dual-Link Active Adapter to assist in testing.