Mysterious Glowing Ball

Description:  The mysterious glowing ball contains a red, green, and blue LED giving the ball a purple appearance. When the ball is stationary your brain perceives them all as one color. When the ball is spinning your brain can perceive individual LEDs turning on and off. The persistence of vision allows technology like movies possible and is a wonderful phenomenon to use in a unit on vision and light.

Web Resource:  Persistence of vision - Wikipedia

Everything is not as it first appears. This simple plastic ball looks purple until you swing it in a circle and reveal its true nature. Inside are three light emitting diodes (LEDs), which are red, green and blue. They turn on and off in sequence very quickly.