The famous Cornsweet illusion or Craik–O’Brien–Cornsweet illusion or Craik–Cornsweet illusion. In this illusion, the entire right region looks slightly lighter than the left area where as the brightness of both areas is exactly the same.
Don’t believe us? See this image, here only the space is added in between those two portions and blackened out.
This optical illusion was submitted by Jessica.