Input Lag Of Monitors

Additional information

How input lag is measured

An input lag of 40ms can be seen on the television.

Input lag is not an official specification because it depends on two varying factors: the type of source and the settings of the monitor. The easiest way you can measure it is by connecting a computer to two different monitors and displaying the same timer on both screens. One of them has to be a known quantity, so you either have a measurement on hand or use a virtually instant CRT monitor as a baseline. You can find a timer here. Then, if you take a picture of both screens, the time difference will be your input lag. This is, however, an approximation, because your computer does not necessarily output both signals at the same time. In this example image, an input lag of 40ms (1:06:260 – 1:06:220) is indicated.

How we measure input lag

In our tests, we measure input lag using our own dedicated device we've designed just for this purpose, which sends an image on-screen and records the time it takes for the image to appear in its sensor (learn more about our tool here). This is a lot more accurate than the two screens method. When measuring the input lag using the two screen method, your precision is entirely limited by the frame rate your camera is capable of capturing, introducing a fair margin of error and inconsistency in your measurement.

For example, a camera capable of recording at 240 frames per second will record an image every 4.17 ms (this is the frame time). This means that you can't measure any monitor with a lower input lag than 4 ms accurately.

However, that only ever applies in perfect conditions. Since LCD screens take time to switch from one frame to another, it's difficult to figure out which part of the cycle you are capturing with a picture. You will probably be seeing parts of frames that were either before or after the input appeared on-screen instead of the exact moment of its appearance. It is possible to take a lot of pictures to create a more accurate average, but it would take significantly more time than with a dedicated device while possibly still not being as accurate. In comparison, our tool takes a sample multiple thousand times a second and is synchronized with its own output, allowing us to precisely find the moment the input appeared on the screen very easily.

Why there is input lag on monitors

There are three main functions that delay the monitor: acquiring the source image, processing the image, and displaying it.

Acquisition of the image

The more time it takes for the monitor to receive the source image, the more input lag there will be. With PCs, this has never really been an issue since previous analog signals were virtually instant and current digital interfaces like DisplayPort and HDMI have next to no inherent latency. Other than from the display itself, the other major cause of input lag in the chain is the device the input was first acquired on. Some mice, usually wireless ones, can add a significant amount of input lag before the image even reaches the screen.

Video Processing

Once the image is in a format understandable by the monitor's video processor, it will apply at least some processing to alter the image in some way. A few examples:

• Adding overlays (like custom crosshairs)
• Adjusting the colors and brightness
• Scaling it (like 720p to 1080p, or 1080p to UHD)

The time this step takes is affected by the speed of the video processor and the amount of processing needed. Although you cannot control the speed of the processor, you can exercise some control over how many operations it needs to do by enabling and disabling settings. The more settings you enable, the more work the processor needs to achieve.

G-Sync monitors all have the same NVIDIA designed video processor which is made to keep input lag low, making them some of the quickest monitors available today.

Displaying the image

Once the monitor has processed the image, it is ready to be displayed on the screen. This is the step where the video processor sends the image to the screen. The screen cannot change its state instantly, and the amount of time it will take depends on the technology and components of the display. Some monitors feature an "Overdrive" setting that can add an adjustment to make this process faster. This can work well, but it can also introduce unwanted artifacts. We cover this in our motion blur tests.

How to get the best results

PC monitors tend to have a much lower input lag than the average TV, making input lag less of an issue for most people. More sensitive users can adjust settings on most monitors to reduce it even further. As a general rule, try the following (which is how we set up the displays in our tests):

• Set the monitor to Game or Instant Mode
• Disable all picture enhancement settings

Additionally, you can try different combinations of settings/modes/inputs until you arrive at whatever balance of features and input lag that you like.

Related settings

• Some monitors will have a higher input lag when they have to upscale content. To avoid this, you can enable GPU scaling in your graphics card's drivers to offload this task to your computer. It might not produce as sharp of an image, but it should remove any additional input lag.

Other notes

• The input lag varies slightly depending on the frame rate and refresh rate, so games played at 120Hz tend to feel more responsive than those played at 30Hz.
• The input lag also varies in time. On some monitors, it even varies +/- 5ms.
• The input lag of your monitor is not the only component in the chain. While the lag produced by your computer might be marginal, wireless mice, keyboards, and controllers tend to have significantly higher latency.

Conclusion

Input lag is the amount of time that elapses between performing an action with a source device and seeing the result onscreen. It’s important for general usage of a computer with a mouse and is particularly important for fast-paced, competitive games. Anything below 20 ms is not an issue for most people. We test to find the lowest amount of lag a monitor can have, as well as how much lag is present when a monitor is displaying a non-native resolution, or when it has features enabled such as HDR or Variable Refresh Rate.