When playing online games on a computer or console the image you see may not be the same image your opponent sees, either you or your opponent could be some frames ahead or behind, making for an unfair advantage/disadvantage. Let’s suppose you are the one behind in frames, you could be “in the past” as much as 300 ms (0.3 seconds), which may seem unimportant, but trust me, it is important, to the point of it explaining those “that didn’t hit me” moments or affect your experience making a game unplayable. This begs the question:
What’s Input lag?
Input lag is the time between you press a button and the order appears on screen. The most mentioned part of this is the “Display lag” and it refers to the time your monitor takes to show the image. Most monitor manufacturers do not advertise this very important number and it takes professional reviewers to reveal it to you, it can be as high as 68 ms. This added to other kinds of input lag makes it not rare seeing 300 ms or 0.3 seconds input lags.
Types of Input lag (from less to more impactful)
Controller or mouse lag:
This is the most negligible kind of Input lag, it depends on the polling rate of your mouse, a 1000 Hz mouse polling rate means your mouse report it’s position to the computer 1000 times per second, which amount for an almost meaningless 1 ms lag. Although worrying about having a good mouse is still important because it helps you aim faster and more precisely. Check your mouse's or controller software configuration to see if the Report rate it is at 1000Hz:
PC and console processing capability:
PC’s and consoles are the one in charge of sending the image to display in the first place. How many frames your CPU/GPU send a second to a display adds to Input lag, for example if you have a 60 Hz monitor coupled with a 60 FPS capable computer, there is going to be sent 60 frames per second, so 1000 milliseconds divided 60 equals 16.67 ms delay. Now let's take this example to the extremes, with 30 FPS you have 33 ms delay and with 240 FPS (and 240 Hz monitor) you have only 4.17 ms.
What can you do to get better Frames Per Second?
Display lag:
This is one of the most important kinds of Input lags, and often confused with Input lag itself. Display lag is the amount of time it takes for a monitor to render an image, this is due to image processing such as motion smoothing, edge smoothing and upscaling. Most monitor manufacturers do not say how bad is their input lag, professional reviewers end up doing this job. Display lag can be as high as 68 ms and as low as 1 ms.
This image from 3d vision blog shows an input lag measurement. It's the same computer with two 120 Hz screens connected. As you can see there is a 9 ms input lag difference. Screen in the left shows images 9 ms faster than screen in the right. Knowing one of the screen's display lag you will know the other screen's display lag too.
How to measure Display Lag if I don't have 2 screens?
Manufacturer tend not to make display lag publics unless this is the selling point. for that reason there are databases where you can find your monitor's model and display lag measurement: https://displaylag.com/display-database/
Network lag:
This only applies to online gaming, nonetheless it is the most significant as it can amount to 500 ms and more and seeing ~100 ms is not rare. It depends on your type of internet connection (wired connection is better than wifi), internet provider (optic fiber is way better than cable internet and 4g) and geographical closeness to the server you’re playing on.
This is exactly what most people call lag and the usual blame factor in games -either if someone really has lag or won't recognize their incompetence in the game-.
How to lower Network lag?
Lastly hire a good Internet Service Provider. The options above are really meaningless if you have google fiber internet or any kind of very good connection. Here are the best ISP's for gaming in 2019 by PCMAG:
How does Input lag affects gaming?
If we add up all the worst cases in the mentioned kinds of input lag we get 600 ms lag, now this is an extreme case, for the sake of argument let’s suppose two people living in the United States, one in the east coast and the other in the west coast, both playing o west coast server. The one in the east coast will have conservatively 100 ms more than the one in the west coast. Now add to this that the gamer playing with high ping is playing on a cheap laptop that runs 30 FPS and with a 60 ms display lag.
All this added up makes for a 200 ms difference between the two players, they might be equally skilled, but the difference in Input lag makes for one winning over the other. Input lag is very important.
Testing has shown that overall input lags of approximately 200 ms are distracting to the user. Imagine trying to play Super Smash Ultimate and having a huge display lag, fighting games require to have instant response times to react and execute combos. Add to the mix a bad internet connection, not only you will have the usual but constant Input lag, but it will also vary and cause confusion. You will be at a significant disadvantage.
In conclusion you should work to improve your input lag with emphasis in the latest points first as they are the most significant, calling your internet service provider is free and could fix most of your problems.
To improve your Display lag you can change the settings in your monitor to get any post-processing to the minimum, you can buy a new monitor that you know and is advertised as having low input lag.
Infographic: