the location of light sensor

Hi, I was wondering what is the recommended location for the light sensor. According to the website (, we should put it near the edge of the screen. But we have found that the delay between the event codes sent from the computer and the onset detected by lightsensor is different if we put the lightsesor on the top-right of the screen or the bottom-right of the screen. The delay with top-right lightsensor is smaller. From the above website, it seems to suggest that middle-right is the best location of the light sensor. Am I right? Or should I choose the location where the smallest delay is found?

Back in the old days of the CRT monitors, the recommended position would have been the same vertical position as the stimulus. That’s because the screen was refreshed vertically, usually from top to bottom.

With the current flat LCD monitors, there is no need to refresh anything. The screen is updated, usually 60 times a second, and the way that they get updated changes from one LCD model to another. It also depends as well on the video card. So unfortunately, we cannot recommend a light sensor patch position.