Buying a monitor can be a complicated process because there are so many factors to keep track of. From the brightness to the size, the resolution, ports, and syncing features; there's a lot to consider. If you're buying a gaming monitor, though, one of the most important factors to consider is monitor response time vs. input lag vs. refresh rate. All of these features can play a part in how smooth and responsive a monitor feels, and how fluid what's on the screen can look.
This is especially important with gaming monitors, where faster response times and refresh rates can have a massive impact on how good a game looks and feels to play, while a low input lag is a must if you're a competitive gamer.
Intro: Brief History of Monitor Technology
Like buying any piece of technology, it's useful to understand the underlying specifications of any monitor you're considering, because then you can get a monitor that is perfectly suited to your wants, needs, and budget. Where resolution is a relatively mainstream specification that most people can wrap their head around – you only really need to consider 1080p, 1440p, and 4k, unless you're looking at ultrawide – that's not the case with response time, input lag, and refresh rate.
These are three distinct numbers that mean very different things, but could quite easily get mixed up with one another if you're not aware of what they actually mean and where they've come from.
Response times are the measurement of how long it takes a pixel to change color, and were a factor on old CRT monitors, too. However, it was rarely given as any kind of metric, since CRT monitors can change color almost instantaneously, while newer OLED and LCD monitors are slower, even if modern displays have become much faster over the years.
Input lag is the measurement of the time it takes between the user making input and it registering on screen, and monitor processing plays a part in that. CRT monitors would typically have very low input lag due to their analog components not requiring any kind of digital processing. However, input lag has been lowered considerably with modern display technologies, with OLED in particular competing with the best CRT monitors for low input lag. Modern LCD monitors are much faster than they were in the past, too, with higher refresh rates and other improvements helping to bring down input lag to near-CRT levels.
Refresh rate is the number of times the screen can update its image per second, and is given in a Hertz (Hz) rating. Introduced with CRT monitors as vertical refresh rate, or vertical scan rate, it was a requirement of CRT technology to update the screen frequently because the phosphors would fade, leading to the image disappearing. CRT monitor refresh rates were twinned with the resolution, however, so higher resolutions meant lower refresh rates, though some CRTs could display high resolutions like 1440p at up to 80Hz, and some could reach 120Hz at lower resolutions.
Modern LCD and OLED monitors can reach much higher refresh rates, however, with 120Hz being common on mainstream gaming monitors and TVs, and specialized displays able to reach as high as 360Hz.
Monitor Response Time
A monitor's response time is the time it takes for a single pixel to change, with most modern displays managing to do so in under 10 milliseconds (ms). Gaming displays, and those that are particularly fast, can do so in less than 1 ms.
The reason a faster pixel change rate is preferred is that motion looks more clear. If a pixel takes too long to change from one color to another, or from one monochrome tone to another, it can lag behind the movement of what's on screen. That can result in a "ghosting" trail behind moving objects on screen, where some parts of the moving element appear in a semi-translucent form behind it.
This is particularly problematic in high-paced gaming, where you need to be both fast and accurate, and having inaccurate information displayed on the screen can be confusing and even detrimental in competitive play. It can also cause issues with watching fast-moving content, like sports, or action movies, too, since that motion blur can still be present and lead to a lower-quality image.
You don't need the fastest of response times if you're just looking for a monitor for work or casual gaming, but keeping it under 5ms means you won't notice it in day-to-day use. If you're looking to do any kind of fast-paced gaming, however, especially if it's competitive, then the lower the better; though most people won't be able to discern much difference between 0.1ms and 1ms response times.
Input lag is a colloquialism rating that in the context of displays, means the delay introduced by the display itself in processing and displaying the images on the screen. However, the actual input lag between the user pressing a button on a keyboard, mouse, or controller, and seeing that appear on the screen is affected by a range of factors.
You could argue that the player's own reaction times impact input lag, but if we assume perfect reaction times, there will be a slight delay from the input device itself, where the keyboard or other peripheral has to register the input. It then has to be picked up by the USB port – with higher polling rates registering actions more frequently, and therefore faster. The CPU has to then process the effect of the input, and send it through to the graphics card, which then renders the effect of the action and sends it to the display. The monitor then applies its own processing, before showing what the user did on screen.
When buying a monitor or display of any kind, the processing of the digital signal and showing it on screen takes some time. Factors like upscaling, or automatic image adjustment can add additional latency, increasing input lag, which is why many modern TVs come with a specific Game Mode, which cuts out those additional processing steps for a more responsive TV. AMD and Nvidia also have their own low latency modes which reduce input lag further, but that's unrelated to a monitor's input lag.
Monitors don't tend to have those optional features, but they do still have their own input lag. Input lag is lower on higher refresh rate monitors, and on those using OLED technology. Enabling V-Sync can increase input lag, so disabling that in games or drivers is a good idea.
Ultimately, input lag is something that's more felt than seen, since it's measured in microseconds, but a lower input lag has a real benefit for competitive gaming, so if you want to play at your best, getting a monitor with a low input lag can help.
A monitor's refresh rate, given in Hz, is the number of times the monitor changes what's on screen per second. So, a monitor operating at a standard rate of 60Hz will update what's on screen 60 times per second. A high refresh rate gaming monitor, however, may do so at a much greater rate, with some monitors supporting 120Hz, 240Hz, and even 360Hz refresh rates, meaning they can update the picture on the screen as many as 360 times per second.
The refresh rate is distinct from the source system's frame rate, which is a rating of how many pictures are generated by the source device, such as a desktop or laptop computer, per second. There are technologies like Nvidia's G-Sync and AMD's Freesync which make the frame rate and refresh rate synchronize for improved image quality. These are sometimes known as dynamic refresh rates, or variable refresh rates (VRR).
Although most mainstream monitors, or those designed with business use in mind, tend to have a 60Hz refresh rate, there are many reasons why you might prefer or benefit from, using a higher refresh rate monitor. In games, higher refresh rates lead to smoother animations, if you can keep the frame rate high. A character moving at 120 frames per second, with a 120Hz refresh rate, will update the picture more frequently with new information. That makes the movement look smoother and more natural.
That's even obvious when using a computer for non-gaming tasks. Just moving the mouse around on the desktop looks and feels far smoother at 144Hz than it does at 60Hz.
There are diminishing returns on this effect as you reach higher refresh rates, but some gamers claim to be able to see the difference between 144Hz and 240Hz, and some even say they can see the difference at 360Hz.
Those extra visible frames also give a slight advantage in competitive multiplayer games. A gamer with a high refresh rate monitor with high frame rates has a picture that updates more frequently with more accurate information. They will have a few-millisecond information advantage over their competition who's gaming on slower monitors.
The final advantage offered by a higher refresh rate is a reduction in input lag. Not monitor input lag, but the overall latency between the gamer seeing something on the screen and reacting to it. Since a higher refresh rate displays new content more regularly, a gamer on a higher refresh rate monitor will be able to see something faster, giving them a few milliseconds advantage.
For example, the time between frames when running a 60Hz refresh rate is 16.67 ms, while a 120Hz refresh rate has an input lag of 8.33 ms. Go up to 360Hz, and it's a mere 2.78 ms, giving someone playing at that refresh rate a notable advantage over those playing on standard 60Hz monitors.
High refresh rates can be quite demanding on the monitor's connector, though, with the highest refresh rate monitors needing powerful connections to receive all the information they need to display. The latest generation of DisplayPort 2.1 connections could open up even greater refresh rates, with the new AMD RX 7000 graphics cards able to support 4K resolution at up to 240Hz, and 1080p resolution at up to 900Hz – although no displays yet exist that could take advantage of such a feature.
Monitor Response Time vs. Input Lag vs. Refresh Rate
Understanding how monitor response time vs. input lag vs. refresh rate affect one another, and ultimately change the look and feel of a monitor is important if you want to use your monitor for watching sports, or other high-paced action, but it's especially important if you want to use it for fast-paced gaming.
Response time is most important when it comes to the look of a monitor. A high response time rating means that you'll see ghosting behind everything that moves around on the screen and you're likely to miss your target if trying to aim quickly. Low response times simply ensure that what you see on screen is how it should be; even if it's moving super fast.
Refresh rates affect how what's on screen can look and feel, so opting for higher refresh rates can make for a smoother experience using the computer, whether you're gaming or just browsing the web. However, it has its greatest effect in gaming, where lower refresh rates can make certain games look a little clunky, while higher refresh rates can make them feel incredibly smooth in comparison.
Higher refresh rates are the most important for competitive games, however, where having a higher refresh rate monitor gives you a distinct advantage over those with slower monitors. You'll see information faster, and with the effect refresh rates have on input lag, you'll react faster too.
All else being equal, a gamer on a high refresh rate monitor will beat one on a lower refresh rate monitor every time. Everything usually isn't equal, so it's never that cut and dry, but it's worth bearing in mind if you take your gaming seriously. Just make sure that you have an HDMI 2.1 or DisplayPort 1.4 or 2.1 connection to take full advantage of your monitors' high resolution and refresh rate at the same time.
Input lag is only really important for competitive gaming. Although there is a slight input lag for every interaction on a computer, it's so minuscule on even slower monitors, that it only really matters if you're trying to get every microsecond advantage in a multiplayer game. Lower input lags ensure that you'll react faster than your opponent, giving you that split-second advantage to help stay ahead of the competition.