Black & white - Source of colors! (Benham’s disk)

Benham's disk

EQUIPMENTS:

1. An old disk/CD/DVD. (Which you don’t want anymore)
2. Glue (Can be obtained from a general store)
3. Scissor (Can be obtained from a general store)
4. White sheet (Can be obtained from a general store)
5. Black marker (Can be obtained from a general store)
6. A rotator (For this you can use things such as – electric motor, electric screwdriver, turntable, hand drill or maybe a toy top.) (Can be obtained from places such as electronic shop, hardware shop, toy shop etc.)

[Warning: Be careful if you are using an electric screwdriver or a hand drill.]

INSTRUCTIONS:

1. Use the scissor to cut the white sheet to give it the same size of the disk (CD/DVD).
2. Use the black marker to color half of the circular white sheet into black. You can fold the circular white sheet so that you can have two equal sides. Then you can color one side which will be half of the sheet to make it black & white.
3.    Now glue the circular white sheet to one side of the disk. Now the disk can be called the name “Benham’s disk” which is obviously.
4. Now you have to use some kind of rotator to rotate the black & white Benham’s disk. To rotate the disk the top of the rotator must be attached at the middle point of the disk (CD/DVD). You can place the disk on a turntable, small electric motor, electric screwdriver, hand drill or some kind of toy top. You can use glue to attach the disk on top of a rotator.
5. Now make the disk rotate. Make sure that there is a lot of light around.
6. Now observe what happens!

RESULTS:

1. Colors will appear as the disk spins.
2. The rotation speed of the disk will impact the appearing colors.
3. Different people may notice colors of different intensities.

Rotating Benham's disk

EXPLANATIONS:

The retina of our eye is responsible for sensing or detecting light and color. There are two different kinds of cells in the retina. They are – rods and cons. Rods help us see in low light conditions. Cons helps us to see in bright light. Cons are also important for color vision.

There are three types of cons altogether. Each cone can sense or detect different colors of light. These colors are – RED, GREEN & BLUE. Each type of cone needs a different amount of time to respond to a color. Furthermore, the cones continue to respond to a color stimulus even after it is gone! But they differ in the amount of time they do so.

We don’t totally understand what happens when we look at the Benham’s disk. But one theory about it is that the black & white areas stimulate different parts of the retina almost at the same time. The white area of the disk activates all three types of cones (Because white is the reflection of all colors in a certain ratio!). On the other hand the black area of the disk deactivates all three types of cones (Because black is the absorption or absence of any or all kinds of colors!!).

When the Benham’s disk is rotating, the black & white side switch places simultaneously and this happens really very fast. So a series of quick cone activation and deactivation takes place in our eyes retina. The activation and deactivation happens so quickly that the nervous system of our eye can’t keep up with it and gets confused. This results an illusion of bands of colors on the top of the rotating black & white disk.

It may show different color bands at different rotating speed, different brightness of light, different kinds of light etc. Different people will see different kinds of colors watching the same disk at the same time because everyone’s eyes have a different distribution of cones on the retina of their eyes. The sensitivity of their cones are also different.

MORE EXPLANATIONS:

In the year 1894, C.E Benham, a toy maker mounted black and white patterns on spinning tops. He marketed those spinning tops under the name “Artificial Spectrum Top”. However, the effect was first discovered in the year 1838 by Gustav Fechner. That’s why the colors which can be seen on the rotating black & white Benham’s disk is often called or referred to as Fechner’s colors.

MORE EXPERIMENTS FOR YOU:

1. Use different kinds of rotating speed to see the color effects.
2. Use different kinds of lights to see the color effects.
3. Look through different kinds of lances to see if anything happens.