Benham’s Disk
A spinning black-and-white disk that tricks your brain into seeing color. The arcs stimulate your retinal cones at different timings, creating phantom hues known as Fechner colors.
About this lab
In 1894, the English toymaker Charles Benham marketed a spinning top painted with a specific black-and-white pattern. When spun, observers reported seeing faint bands of color—reds, greens, and blues—where none physically existed. These are called Fechner colors or subjective colors.
The illusion exploits differences in how quickly your three types of color-sensing cone cells respond to changes in light. When the black-and-white pattern sweeps across your retina, the rapid alternation of light and dark stimulates your red, green, and blue cones at slightly different rates. Your red cones respond slightly faster than blue cones, so arcs at different radial positions—which spend different amounts of time in the light or dark phase—create different apparent hues.
Reversing the spin direction changes which cones are stimulated first, which is why the perceived colors shift. The effect is stronger at moderate speeds (6–12 RPM) and varies between individuals. Some people see vivid colors; others see only faint tints. The colors are entirely in your visual system—a camera would record only black and white.
Try changing the speed and direction to find the combination that produces the strongest colors for your eyes. The classic Benham pattern uses concentric arc groups at different radii, each tuned to elicit a different apparent hue.