Two of every three squares covered in white: each square left is the same gray all round, with no bright corners.
Lighter or darker?
Vasarely illusion
Do you see a bright X from corner to corner?
It isn’t there: each square is one even gray all round.
Why? At each corner, a square has a darker square on two sides instead of one, so your eye brightens it a little more. The corners line up into an X. Victor Vasarely used it in his paintings.
Picture: Drawn by Science Playground