Persistence of Vision

When you look at a series of sequential images an amazing thing happens. If the images are shown quickly enough you do not see the separate images, rather you see a smooth moving animation. This phenomenon, called “persistence of vision”, is where the individual image “persists” or is preserved for a fraction of a second, making the visual appearance of continuous motion.

If the images are presented fast enough, the resulting motion will appear continuous. However, if the images appear slow, the motion will appear jerky and discontinuous. The rate at which the images appear is called the “frame rate”. This term comes from film industry where sequential images are stored on film, and are the basis of movies and video. Typical frame rates for movies and video are approximately 25 frames per second. This means that the eye and brain have only 0.04 seconds to process the information for each image!

Another example of persistence of vision we encounter everyday is electric lighting. Many of the lights that we use to illuminate our homes and offices are actually turning on and off very rapidly. At a high rate the eye and the brain interpret the flashing lights as a continuous source, and no flickering is perceived.

The WavyWand™

The WavyWand™ is based on this visual perception of persistence of vision. For the WavyWand™ to operate correctly there are four critical components: a motion sensor, a computer, a series of LED’s (Light Emitting Diodes), and a motion source--That’s You! As you wave the WavyWand™ the LED’s are turning on and off very rapidly, at the rate of over 1250 times per second. The time and position where the LED’s are turned on and off is controlled by the computer and based on the image that will be displayed and the waving motion as measured by the motion sensor.

As the WavyWand™ is waved from side to side; each of the LED’s is turned on and off in a specific pattern. With persistence of vision this pattern is interpreted by the eye and the brain as an image. Because the WavyWand is moving pretty fast, the patterns or images will appear not on the Wand but seemingly in mid–air. Like with movies and videos, the WavyWand can also show animations by displaying a sequence of images in succession.

Other Persistence of Vision Examples

Some other examples of toys and devices that use the persistence of vision phenomenon are:

  • Flip Books
  • Thaumatropes
  • Zoetropes
  • Television
  • Movies/Video
  • Fluorescent Lights
  • Computer Monitors

Further Reading and Links
http://en.wikipedia.org/wiki/Persistence_of_vision

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