PURPOSE: Classic Cornsweet illusion with circular rotating discs.
DESCRIPTION: The disc shown above is painted half black and half white, with the patterns shown in the photograph. A disc without the patterns would appear a uniform shade of gray when rotated by a high-speed rotator. The pattern above, however, produces four different shades of gray, the lightest inside and the darkest outside, due to the construction of the patterns.
This effect is due to the fact that the eye responds more strongly to rapid changes in black/white density (the sharp edges) than to smoother changes.
Another disc is available that includes only one junction, where the outside segment appears darker than the inside segment. When the junction is covered by a ring, the two segments look the same shade of gray.
REFERENCES: (PIRA 6J11.42)
EQUIPMENT: Fast rotator with discs.
SETUP TIME: None.
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