Hii, my experiment consist in a black rotating dot with a background light to generate contrast. When I keep all conditions the same only changing the light intensity of the background light I notice that there is like a time delay or a latency (I dont know how to call it) between the position of the OFF and ON events.

In the image you can notice that the location of the ON events from the OFF events is more distant in low light conditions. I have tried to understand the relationship of light to space-time for this case, but it is not very clear to me. 

Thank you so much for your help.