PURPOSE: Demonstrate positive and negative color afterimages.
DESCRIPTION: A half white and half black disc with a small cutout is rotated a few revolutions per second with a red light bulb visible through the cutout. When the black segment follows the cutout (counterclockwise rotation) a red afterimage is seen, due to saturation of the red cones while the bulb is visible. When the white segment follows the cutout (clockwise rotation) a cyan afterimage is seen, the complementary color to red. Because the red cones are saturated by direct viewing of the bulb, the white field activates the green and blue cones more strongly, producing a negative afterimage.
A 100 watt goose neck lamp is used to produce a strong white surface.
REFERENCES: (PIRA 6J11.10)
EQUIPMENT: Slow rotator with half-black and half-white disc with cutout, goose neck lamp.
SETUP TIME: None.
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