benham1Charles Benhamho (1895) created a toy top painted with the pattern (images on next page). When you spin the disk, arcs of color (called “pattern induced flicker colors”) show up around the disk. And different people see different colors!


We can’t really say why this happens, but there are a few interesting theories. Your eyeball has two different ways of seeing light: cones and rods. Cones are used for color vision and for seeing bright light, and there are three types of cones (red, green, and blue). Rods are important for seeing in low light.


One possibility is… [am4show have=’p8;p9;p19;p46;p66;’ guest_error=’Guest error message’ user_error=’User error message’ ]


…how the human eye is tuned for different colors. Your eyeballs respond at different rates to red, green, and blue colors. The spinning disk triggers different parts of the retina. This alternating response may cause some type of interaction within the nervous system that generates colors.


Another theory is that certain cones take longer react, and thus stay active, for longer amounts of time (though we’re still talking milliseconds, here). To put another way, the white color activates all three cones, but then the black deactivates them in a certain sequence, causing your brain to get mixed and unbalanced signals. Your brain does the best it can to figure it out the information it’s getting, and “creates” the colors you see in order to make sense of it all.


Neither of these theories explains the colors of Benham’s disk completely and the reason behind the illusion remains unsolved. Can you help out these baffled scientists?


Materials:




 
Download Student Worksheets & Exercises


All you need to do is download this PDF file and cutout a copy of a disc on the page. Then find a way to spin it at high speeds – you can stick a pencil through the center and spin it like a top, thread string through it and pull to rotate (just like the Mixing Colors Experiment), attach to a drill or mixer or electric screwdriver, or slap it on a motor shaft and engage the power. Which works best?


Exercises


  1. What colors were you able to see when the disks were spinning?
  2. How did the different patterns look when they were spun?
  3.  How did speed and direction affect what you saw?

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Comments

8 Responses to “Benham’s Disk”

  1. Hi Mary,

    I’ve sent you a private message by email. 🙂

    Aurora

  2. Mary Gomes says:

    Hello,

    I am reviewing the Ultimate Science Curriculum and was hoping to print up some things. I do plan to purchase it, once I do will I have access to all the downloads?

    Thank you,

    Mary

  3. Terri Cleary says:

    We used a snap-it electronics kit that had a ‘helicopter’ part to spin our disks, using double-sided scotch tape between the blades and the disk. At first, we did not see color. However, we did see a 3D effect with some disks, which was cool. But then we noticed we could see color when we turned off the power and the disks slowed down. Very neat effect. I saw yellows and yellow-greens. My grandmother (Terri) saw reds and yellows. So we figured I saw just down the spectrum from her. The disks with narrow alternating solid-pattern did not show any color that we could see. It was f-u-u-u-n!
    Xander

  4. Deborah Andrews says:

    We got it to work now thanks!

  5. The PDF file requires Adobe Acrobat to read it, which you can download there. You also can’t download the file unless you’re logged in, so be sure to do that first. I just tried it, and it popped right up… let me know if you still have trouble.

  6. Deborah Andrews says:

    We can’t find the file what should we do?

  7. Whoops – sorry about the bad filename.. try again?

  8. Amy Bowman says:

    The PDF file isn’t there for the Benham’s disk.