How to Use a CD and a Marble to Understand Why Blue Can Look Like White

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Amidst a national debate over whether #TheDress is black and blue or white and gold, Resource Area For Teaching, RAFT, aims to alleviate misunderstanding through demonstrating the science behind color perception. RAFT, an education nonprofit, highlights a simple activity that both children and adults can do to help understand why people see color differently.

Assemble a spinning disc from a CD, marble, and foam to test how your brain perceives color from black and white.

Given the photo quality, limitations of digital photography in translating accurate light levels, and variation in the color sensing nerves from person to person, it is understandable that there is such a discrepancy in how people perceive the dress.

Need a way to explain to children how a dress can appear both blue and white? It’s not a trick, it’s just science.

Amidst a national debate over whether #TheDress is black and blue or white and gold, RAFT aims to alleviate misunderstanding through demonstrating a century-old activity that turns black and white into color.

In 1895, Charles Benham created a spinning top painted with black and white that when spun, caused people to see a variety of colors. RAFT offers free instructions to make one at home using just a CD, marble, piece of foam, adhesive, and free printable image. “Black and White Makes Color” provides a unique way to understand why it’s possible for some people to see blue where others see white. After assembling the disc, have someone give it a spin to see what colors they perceive. While the disc spins, people will see many different colors such as blue, green, or brown. Others will see no colors other than black and white.

The science behind the activity is more complex than spinning the top. Color sensing nerves, called cones, are located on the retina in the back of the eye. Cones come in 3 types: red-sensitive, green-sensitive, and blue-sensitive.

White light is a mix of all the colors in the visible spectrum and causes all three cones to fire, leading the brain to determine that the color is white. Conversely, black is the absence of color and causes no cones to fire, signalling that the color is black.

The spinning CD forces the brain to process both colors, black and white, very quickly as the three cones fire and turn off with every revolution of the disc. It takes a small amount of time for each cone to fire, which is referred to as latency. It also takes a brief time to shut off even after the color is removed, known as persistence. Each of the different types of cone (red, green, and blue) may have a slightly different latency and persistence, explaining why people will interpret different colors from watching the same rotating disc.

Light levels and photo quality also play a critical role in the dress color debate at hand. Cone cells discern color and function best in bright light because the three types of cone cells all send signals to the brain regarding the strength of each color (red, green, and blue). The brain then inserts these relative strengths to mix them, giving colors in between such as orange, indigo, and even gold. The human eye and brain are capable of distinguishing several hundred hues, but given the photo quality, limitations of digital photography in translating accurate light levels, and variation in the color sensing nerves from person to person, it is understandable that there is such a discrepancy in how people perceive the dress.

In addition to “Black and White Makes Color,” RAFT offers more than 700 free instruction guides for educators and parents to engage children in hands-on learning activities covering science, technology, engineering, math, art, and literacy topics. Dozens are also available as pre-packed kits for individual students or larger groups at the RAFT online store: http://www.raftstore.net.

About Resource Area For Teaching
RAFT believes the best way to spark the love of learning for the next generation of thinkers, innovators, problem-solvers and creators is through hands-on learning. A nonprofit organization since 1994, RAFT serves 12,000 educators each year who teach over 900,000 students. Find out more about RAFT and how to get involved at http://www.raft.net.

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Michelle Berg
@RAFTBayArea
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