As you maybe know, I am an expert in optical illusions… So, I would like to show you one of my oldest illusions I created in the 90s. In the picture you may see ghost-like dark radial beams. This illusion is a variant of the Herman’s scintillating grid illusion. I designed this illusion just by turning 45 degrees the Herman grid and then by applying a polar transformation.
The Hermann grid illusion is an optical illusion reported by Ludimar Hermann in 1870. The illusion is characterized by ghost-like gray blobs perceived at the intersections of a white grid on a black background. But I discovered that when you turn the grid 45 degrees an additional visual illusion appears: you may perceive a swarming of orthogonal darker lines! As if the opposite corners of each square are creating illusory flashing diagonals…
The animated version of the illusion is more striking. With the power of your mind, you can make the geometrical pattern rotate clockwise or counter-clockwise (but when the pattern rotates clockwise, you will see the illusive radial beams rotate counter-clockwise, and vice-versa). 
This animated version from Youtube features a rotating white pattern on a black background followed by a rotating black pattern on a white background. The scintillating effect is more apparent on the second variant.
