Answer:
While both input lag and response time are equally important for a fluid gaming experience, too high input lag can make competitive gaming unbearable.
Luckily, most new gaming displays offer both low input lag and quick response time, so you won’t have to compromise.
Many people mistake response time for input lag when looking at the display’s specifications.
To clarify, input lag is the delay between the screen and your commands, such as a press on the keyboard or mouse.
Response time, on the other hand, is the time pixels take to change from one color to another.
Response Time
A quick pixel response time speed is needed to eliminate ghosting (trailing) behind fast-moving objects in fast-paced games.
Just how fast the response time speed needs to be depends on the monitor’s maximum refresh rate.
A 60Hz monitor, for instance, refreshes the image 60 times per second (16.67 milliseconds in between refreshes).
So, if a pixel takes longer than 16.67ms to change from one color to another on a 60Hz display, you will notice ghosting behind fast-moving objects.
For a 144Hz monitor, response time needs to be lower than 6.94ms, for a 240Hz monitor, lower than 4.16ms, etc.
Now, the specified pixel response time speed that monitor manufacturers quote (such as 1ms GtG, 4ms GtG, etc.) refers to the display’s fastest pixel transition possible from one shade of gray to another under certain testing conditions – it’s not the average speed.
Pixels take longer to change from black to white than vice versa, so even if all white-to-black pixel transitions are below the quoted 4ms on a 144Hz monitor, for instance, some dark-to-bright pixel transitions still might take over 10ms.
Consequently, you would get noticeable black smearing in fast-paced scenes with a lot of dark pixels involved, while in other scenes, ghosting wouldn’t be as noticeable.
Generally, if you want to avoid ghosting, you should look for gaming monitors with a specified response time speed of 1ms GtG (Gray to Gray) – or lower.
This, however, won’t guarantee flawless response time performance, which needs to be properly optimized via the monitor’s overdrive implementation.
A good overdrive implementation will ensure that the pixels change fast enough, but it will also prevent inverse ghosting (i.e. pixel overshoot).
Inverse ghosting is characterized as a bright trail following moving objects, which is caused by pixels being pushed too hard via an aggressive overdrive mode.
To find out just how well the overdrive is implemented on a monitor, as well as what setting should be used at which refresh rate, you will need to look for detailed monitor reviews.
How We Test Response Time
We’re using OSRTT (Open Source Response Time Tool) to measure monitor response time and display lag.
This tool measures gamma-corrected pixel transitions. Below is a heatmap from our BenQ Zowie XL2566K review.
The first table shows the initial response time speed, for instance, it takes 1.3ms for pixels to change from an RGB value of 153 to RGB 102.
In this case, the average initial response time is 1.82ms, which is an excellent result for a 360Hz display with a 2.78ms refresh rate cycle. Further, most (90% in this example) pixel transitions are done within the 360Hz window.
The table in the middle shows overshoot, while the table on the right, to put it briefly, illustrates the relation between response time and overshoot in real use. So, a fast transition with minor overshoot (therefore mostly unnoticeable in real use) will score higher than a slower transition with no overshoot.
We also do Blur Busters’ UFO Ghosting Test, which depicts pixel response time performance in real-world use. To keep the tests consistent across different reviews, all displays are first calibrated and warmed up, and we use the same 960 Pixels Per Sec test with the shutter speed set to 1/4 of the refresh rate with fixed focus, ISO and color temperature (6500K).
All overdrive modes are tested at different refresh rates to find the optimal overdrive setting for a given refresh rate. Ideally, that will be a single overdrive mode regardless of the refresh rate (through the use of variable overdrive), though this isn’t always the case.
In some rare cases, overdrive can behave differently at fixed and variable refresh rates. For instance, a ‘Strong’ overdrive mode can look different at fixed 100Hz and when using VRR at 100FPS (therefore 100Hz) on a 144Hz monitor. Since Blur Busters’ ghosting test (done in a web browser) doesn’t support VRR, we run the monitor through the SmoothFrog application to see if this type of behavior is present.
In the image above, you can see different response time behavior. After the reference image, we have the ASUS PG27AQDM 240Hz OLED panel with instantaneous pixel response time speed.
Then we have the Innocn 39G1R with black smearing caused by slow dark-to-bright pixel transitions common for VA panels, followed by the MSI MAG281URF using the aggressive ‘Faster’ overdrive mode that adds too much overshoot.
Lastly, you can see how even if a monitor has nearly instant response times as the PG27AQDM, some motion blur will still be noticeable due to the way the image is created on LED and OLED monitors (sample-and-hold method).
Monitors with MBR (Motion Blur Reduction) can reduce this perceived motion blur by backlight strobing (on LED LCDs) or black frame insertion (on OLED displays).
As a result, you get clearer motion at a cost of reduced brightness and introduced screen flickering. Most MBR implementations cannot work at the same time as VRR and add strobe crosstalk (image duplications), but here (last image) we can see BenQ’s excellent DyAc+ implementation on the Zowie XL2566K.
GtG vs MPRT Response Time
Sometimes, monitor manufacturers will specify a response time speed of 1ms without declaring if it’s a GtG or MPRT (Moving Picture Response Time) measure.
The 1ms MPRT measure usually refers to the backlight strobing technology of the monitor. So, be careful when looking at the specifications and always look for monitor reviews for full information.
With TVs, the pixel response time speed is not specified at all, meaning that online reviews are your only hope to see how fast a certain TV is.
This doesn’t apply to OLED TVs, which have self-emissive pixels that can change instantaneously.
Input Lag
The higher the refresh rate, the lower the input lag.
So, a 120Hz display will have essentially half the input lag in comparison to a 60Hz display since the picture gets updated more frequently and you can react to it sooner.
Pretty much all new high refresh rate gaming monitors have low enough input lag in relation to their refresh rate that the delay between your actions and the result on the screen will be imperceptible.
Therefore, if you want the fastest 240Hz or 360Hz gaming monitor available for competitive gaming, you should focus on its response time speed performance.
TVs usually have higher input lag than monitors.
For the best performance, look for a TV that has a native 120Hz refresh rate (not ‘effective’ or ‘fake 120Hz’ via framerate interpolation)!
It’s also very important to enable the ‘Game Mode’ on the TV. It bypasses certain image post-processing to reduce input lag.
How We Test Input Lag
OSRTT also allows us to measure total system input latency. We then isolate display lag from click time or USB polling rate and processing latency to get how long it takes the monitor to take in a new frame, process it and start drawing it.
Ideally, display lag should be lower than the refresh rate window. So, on a 360Hz monitor, if the display lag is lower than 2.78ms, you won’t be able to notice or feel any delay between your actions and the result on the screen.
Of course, a lot of gamers wouldn’t be able to notice any latency even if it were a bit higher than that, but lower is always better when it comes to lag!
The chart above is from our BenQ XL2566K review, which measured a display lag of only 2.27ms at 360Hz.
