Input lag on TFT monitors
Input lag is the time it takes an image to appear on screen versus the time when the signal was sent by the computer into the monitor cable.
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A traditional CRT monitor which if driven at 200Hz can display an image in 5 milliseconds, or one refresh. Typical TFT monitors today might take over 10 times as long due to input lag. Input lag is caused by the quality and processing speed of the monitors electronics. This can make presentation timing and synchronisation with other equipment a real issue.

What's more input lag varies between makes and models of display as the video below clearly illustrates. If you replaced one TFT monitor for the other on the same PC your experiment generator would continue to present visual stimuli as normal and it would record that it had done so at the time you requested. Unfortunately there is no way for your PC or experiment generator to know about the input lag on a given monitor.

In reality as you can see input lag means that you are not presenting visual stimuli at the same time at all. Input lag also means that the image offset is shifted back by the same amount as the lag. If you are synchronising with other equipment such as EEG, MRI, eye-trackers etc. the image will drift still further out of sync.

Input lag can mean that you are not running the experiment you thought you were and that your results might be questionable.

Read more about input lag on TFT Central

Input lag is the time it takes for a image to actually be displayed on a TFT panel
(this is not the same are panel response time). Here are two different panels
connected to the same graphics card via a splitter to
illustrate the effect.


Input lag on data projectors can be even more problematic as the table below illustrates. When image processing is left at the default settings on many projectors, input lag can more than tripple as demonstrated with the Acer H9500 (shown in bold).

Image processing off Image processing off CFI/motion smoothing on
Sanyo Z200 – 16 ms Mitsubishi HC7800 – 33 ms Panasonic PT-AE7000U – 66 ms
Espon 8350 – 18.5 ms Acer H9500 – 41 ms Mitsubishi HC7800 – 83 ms
Sony HW10 – 10-20 ms Panasonic PT-AE7000U – 41 ms Epson 5010 – 141 ms
Sony HW20 – 16-32 ms JVC RS1 – 50 ms Acer H9500 – 150 ms
Infocus X10 – 25 ms BenQ W5000 – 50 ms BenQ W7000 – 150 ms
Panasonic AR100U – 25 ms BenQ W7000 – 50 ms  
Optoma HD800x – 30 ms JVC RS40 – 70 ms  
Panasonic AE300U – 30 ms Espon 5010 – 81.4 ms  
Sanyo Z3000 – 30 ms Espon 3010 – 100 ms  
Panasonic AE4000 – 33 ms    

Input lag measures for commonly available data projectors
(timing data collated from http://www.avsforum.com)