Homemade Benham's Disk

<strong>Homemade</strong> Benham’s <strong>Disk</strong><br />

In 1894, toymaker C. E. Benham discovered that a spinning disk with a particular pattern of<br />

black and white marks could cause people to see colors. Mr. Benham called his disk an Artificial<br />

Spectrum Top and sold it through Messrs. Newton and Company. <strong>Benham's</strong> Top (or <strong>Benham's</strong><br />

<strong>Disk</strong>) has puzzled scientists for over 100 years.<br />

Here is how to make your own Artificial Spectrum Top:<br />

Make the spinner<br />

Method 1<br />

1. Get the top of a plastic, round container (margarine containers work well) and a<br />

toothpick.<br />

2. Poke a very small hole in the middle of the plastic top. You may have to use a metal nail.<br />

The hole should be smaller than the width of your toothpick.<br />

3. Break or cut the toothpick in half. Insert the pointed end of the toothpick through the<br />

center hole in the plastic top. The toothpick should stick in the hole. (See the picture<br />

below)<br />

4. Twist the toothpick to spin the spinner.<br />

Method 2<br />

1. Get some cardboard and a toothpick.<br />

2. Draw a circle (with a diameter of at least 4 inches) on the cardboard.<br />

3. Cut out the circle carefully. It is important that the circle is as round as possible.<br />

4. Poke a hole in the center of the circle with the toothpick.<br />

5. Insert the toothpick into the hole. The toothpick should stick out about half an inch.<br />

Break or cut the toothpick in half.<br />

6. Twist the toothpick to spin the spinner.<br />

Attach image disk to spinner Carefully cut out each disk. (templates found below)<br />

1. Poke a small hole in the center of the image disk.<br />

2. Place the image disk on your spinner, making sure the toothpick goes through the hole<br />

you just made.<br />

3. The disk should lay flat on the top of the spinner. A glue stick can help to keep it in<br />

place.<br />

4. Spin the spinner and watch what happens. Try each disk pattern and compare the<br />

results.<br />

http://faculty.washington.edu/chudler/benham.html

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Benham’s <strong>Disk</strong> Templates<br />

Instructions:<br />

Cut out each disk carefully. Push a toothpick through the center of each disk and<br />

then slide the toothpick through the middle of the plastic lid or cardboard.<br />

Break the toothpick in half for the best results. The blank disk without a pattern<br />

(lower right) is for you to design yourself. Use a black marker to draw on the<br />

white half. Attach your disk to a spinner and see if it works.<br />

http://faculty.washington.edu/chudler/benham.html

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Special Notes for Using the Spinner<br />

1. The colors are seen best at slow speeds (between 3-5 rotations/second). Try different<br />

speeds!<br />

2. It is important that your spinner can spin at slow speeds. Therefore, make sure your<br />

spinner is centered properly. Make sure you place the toothpick in the center of the<br />

spinner.<br />

3. Experiment!<br />

• Change the lighting conditions. Test it outside in sunlight; test it under different<br />

types of light (incandescent, fluorescent, etc.)<br />

• Change the pattern. Make your own pattern using the blank disk. Use a black marker<br />

to draw a pattern or series of arcs on the white side of the disk.<br />

• Change the color of the disk. What happens if you use a blue disk?<br />

• Spin the spinner clockwise and counterclockwise.<br />

Theories for How the Benham’s <strong>Disk</strong> Works<br />

The retina of the eye is composed of two types of light-sensitive receptors: cones and rods.<br />

Cones are important for color vision and for seeing in bright light. There are three types of<br />

cones, each of which is most sensitive to a particular wavelength of light. Rods are<br />

important for seeing in low light.<br />

It is possible that the colors seen in spinning Benham disks are the result of changes that<br />

occur in the retina and other parts of the visual system. For example, the spinning disks may<br />

activate neighboring areas of the retina differently. In other words, the black and white<br />

areas of the disk stimulate different parts of the retina. This alternating response may cause<br />

some type of interaction within the nervous system that generates colors.<br />

Another theory is that different types of cones take different amounts of time to respond<br />

and that they stay activated for different amounts of time. Therefore, when you spin the<br />

disk, the white color activates all three types of cones, but then the black deactivates them.<br />

The activation/deactivation sequence causes an imbalance because the different types of<br />

cones take different amounts of time to respond and to stay on. This imbalance in<br />

information going to the brain results in colors.<br />

Neither of these theories explains the colors of <strong>Benham's</strong> disk completely, and the reason<br />

behind the illusion remains unsolved.<br />

http://faculty.washington.edu/chudler/benham.html