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BenQ Knowledge Center

Gaming Monitor Input Lag Versus Response Time: What’s the Difference and Why Should I Care?

BenQ
2020/01/06

If you’re looking to get a new gaming monitor, whether 60Hz, 144Hz, or even 240Hz, then you’re most likely considering two very important specs. We don’t mean resolution as that’s a given and the first item on the list right next to screen size. We’re referring to input lag and response time. While most prospective gaming monitor shoppers know what refresh (or frame) rate means, quite a few people remain confused about the distinction between response time and input lag.

Additionally, while almost every gaming monitor has a response time listed in the spec section, input lag rarely makes an appearance. That’s because while the confusion exists, the two terms are very different. Manufacturers can easily calculate and test monitor response times at the factory, but input lag (or input latency) presents a much more complex issue. Many factors that go into input lag have nothing to do with the monitor or the production process used to make the display, and so manufacturers would be remiss if they made bold input lag claims.

Despite that, as someone interested in gaming and gaming monitors you should definitely educate yourself on these two related but distinct terms. That’s because if you opt for a cheap monitor that ends up having slow response or lots of lag then your gaming may well be ruined. Even monitors with high refresh rates can be slow in this regard. If they suffer from sluggish response time and high latency your games will present with problems like motion blur and ghosting. Additionally, controlling in-game actions will feel “off” and unresponsive. That’s why gamers really should learn more about response time and input lag plus how the two differ. 

Why the confusion in the first place?

Quite a simple answer to that one. Response time forms a part of overall input latency. That most likely explains why so many people misunderstand that the two specs describe different but connected aspects of a gaming monitor. Another cause for confusion may originate in the fact that both refer to speed and have become part of the popular discussion around gaming monitors as things to consider for optimal monitor performance. Often mentioned in the same sentence, response time and input latency sometimes become conflated with each other.

Sure, both tell us important things about a gaming monitor’s speed, but from very different angles. Response time is entirely native to the monitor proper, while input lag or latency include the whole process from you pressing a button to a corresponding action occurring onscreen.

Distilled to their bare essence, both terms detail the speed with which images change on a display and react to your input. But that’s a very simplistic description that doesn’t do the topic justice, so let’s look at them up close. 

All-important responsive pixels

Response describes the length of time a given monitor or panel needs to change the properties of each pixel. Since TFT LCDs consist of millions of pixels (or transistors), for example 8.3 million in a 4K monitor, speed is understandably of the essence. Response time tells us how long a monitor needs to turn a pixel from red to green, as an example. The faster, the more responsive the image updates. Faster means smoother display and allows for higher refresh rates.

Monitor manufacturers list GtG response times, or grey to grey. That’s because switching pixels between different shades of grey is a lot quicker than changing among base colors (RGB). That’s not a trick, the number given still provides an excellent indication of monitor speed. GtG response times of under 5ms are OK for gaming, though you really want to be at 1ms. Clearly, a zero isn’t possible with current technology so don’t expect that. Or believe anyone that claims it.

Think of response time like this. You’re playing a first person game and decide to turn left, down an alley. Your monitor gets the data from your PC or console and needs to update the image you see to reflect the new graphics being loaded in. A monitor with 5ms technically does this five times slower than a 1ms screen. Of course, we’re talking about milliseconds so the difference may not be perceptible. But every little bit counts as games by nature need to be responsive, and like we said response time contributes to overall lag or delay.

Different gaming monitor panel types support slightly diverse response times, although advancing technology has helped narrow down gaps. The fastest response occurs on TN panels, which generally are the best for reflex-based gaming. Essentially all TN panels do 1ms these days, which is why they’re the only ones capable of 240Hz refresh rates, as well. VA and IPS panels usually come in at 2ms-5ms but provide better colors and viewing angles. We’ve discussed panel technologies if you want to know more.

TN panels carry out the least pixel processing of the three main panel types, explaining their high speeds. VA and IPS panels have been designed to ensure better colors, but that requires more processing – meaning delays. As the simplest mainstream panel type, TN manages the fastest response times by getting straight to the pixel, so to speak.

Keep in mind that due to physics, the bigger the screen the slower the response time. Likewise, the higher the resolution the slower the response. Bigger means signals have to travel farther from the monitor’s main power and processing sources, and higher resolution means more pixels to update. A big however here, though. Thanks to ever-better technology, current monitors are very good at overcoming these hurdles. In actual terms there’s almost no difference these days between 24” and 32” monitors, and 4K screens perform just as fast as 1080p monitors. 

From press to display

The total time required to show an action on the screen amounts to what is known as input lag. The word input mostly refers to you, the user. You press a key or click a button on a keyboard or controller and then expect a corresponding action on your gaming monitor (or TV). The time needed to show you that action equals input lag.

Input lag rises from a host of factors. From your controller or keyboard the signal moves to your PC or console. If you’re using wireless input devices that movement takes a little longer than with wired versions. Then your PC or console take time to process the data you gave them, then more time to send graphics info via a cable to your display. Generally, HDMI and DisplayPort have the same speed: light speed. So cables aren’t a major issue, but they’re a step. Then every monitor has processing units that accept signals and work to update the screen. Thus, the monitor’s internal circuitry introduces lag. Response time factors into latency as we mentioned above. That means the time a monitor needs to get a signal, process that signal, then change its pixels to depict visuals obviously adds latency.

Any image processing done on your monitor increases latency. Even if base response time is 1ms, should the monitor then add refinements like HDR, dynamic brightness/contrast, edge sharpening, local dimming and so forth – well, latency increases. Remember the basic rule: image processing means lag.

That’s why for gaming we recommend using PC mode or game mode. Those switch off most image processing to keep you close to raw response time on the monitor. How do we measure input lag? Also in milliseconds, but it’s a lot more than response time. Really good monitors like the BenQ EL2870U,  the 4K HDR monitor EW3270U, and 144hz gaming monitor EX2780Q with speakers clock in at 9ms-10ms based on third party reviews, but the average hovers somewhere between 15ms and 22ms for typical gaming monitors and gaming-minded TVs. You should not detect any negative effects with those latency figures, and your games will feel very responsive. It’s only when latency exceeds 40ms or so that people begin to notice sync issues. Anything over 50ms would be basically unplayable. Don’t laugh, lots of cheap monitors and TVs even now deliver performance slower than that, resulting in completely ruined gaming experiences. 

Take your time – it’s the monitor that should be fast

When shopping for a gaming monitor do some research, read reviews, and check out the spec sheets. You’ll likely find out about each model’s response time easily enough, but reviews and forum posts will shed more light on input lag. Stay with reputable, established brands. Get monitors that specifically mention gaming, as good manufacturers won’t claim gaming-grade performance for slow monitors, it’s simple as that.

Also simple is the difference between response time and input latency. The former is local to the monitor and helps you understand how fast the panel is on its own. The latter refers to a much more comprehensive and useful number because it includes response time and illustrates the actual gaming experience you’ll have with a monitor or TV.

Now you know! Don’t rush and get a monitor to make you happy.

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