How can I measure the input lag/latency of my monitor?

Question

I want to determine the input lag of my monitor (actually, it's a projector) because I noticed that there is a considerable latency between my mouse/keyboard actions and the screen. I have found a few videos using this tool, however, I cannot read off the milliseconds as they are completely smeared out.

Is there an alternative way?

Solution 1

One common way is to use a reference screen with negligible or known input lag in Clone mode. E.g. connecting the monitor to a laptop, the laptop screen can (usually) be assumed to have negligible input lag.

Then use a software clock showing milliseconds and take a photo of the two screens. The difference between the milliseconds shown on the two displays in the photo (plus the input lag of the reference screen, if any) is the input lag.

In some cases, however, due to the slow reaction time of many displays, the milliseconds can hardly be read off. You can use this special millisecond clock which stores the milliseconds in a number of separate fields to overcome this problem

Solution 2

There's nothing that you can do that's free, because the alternatives require hardware. But at the cheapest, the hardware required is just $5. in ascending cost, your options are:

free: piLagTester (but requires raspberry pi 0, which costs $5). https://alantechreview.blogspot.com/2020/05/a-5-tv-input-lag-tester-using-raspberry.html

$40+: piLagTesterPRO (requires raspberry pi 0): https://alantechreview.blogspot.com/2020/08/pilagtester-pro-order-page.html

these two above are the cheapest options but require typing a few linux commands to use. If you'd rather spend more for a simple box that you just plug in there are two additional options:

$80-100: time sleuth https://castlemaniagames.com/products/time-sleuth-display-lag-tester

$125: leo bodnar input lag tester https://www.leobodnar.com/shop/?main_page=product_info&products_id=212

all 4 of these are the same level of accuracy, and drive your monitor directly. Thus they can measure your monitor's input lag with high accuracy. BUT they cannot determine if there's something about your computer/OS or video card that's adding additional latency. Given that you are reporting smear, however, the lag is probably your monitor's slow response time.