Look at the center of a figure and try moving closer and further from the figure semi-quickly. The effect is a change in the apparent brightness.
We call the effect the "Here comes the sun" effect
The effect occurs regardless of the number of stripes.
The phenomenon is sometimes even stronger with blurred figures.
Notice the changes both toward the center and at the outer edges in this extension.
The illusion does not occur if the figure is posterized and has just five gray steps
Or ten steps.
But effect does occur to some degree when the number of steps increases to twenty and the figure begins to approximate those with continuous, gradual change.
The effect also does not work when the figure is broken into a mosaic.
Interesting variations can happen with variations in hue.