Eyes (Level 1)

Scattering in a Beaker of Milk
The colors of many things come from scattered light. Milk is white because it scatters almost all the light that hits it. This picture shows a glass beaker full of water with just a little bit of milk in it. The beaker was lit from the side. On the left the camera was above the milk and water and the light scattered sideways was blue. On the right side, the camera was across from the light on the side of the beaker and we can see the red light that passes through without being scattered to the side. This shows why the sky is blue (light scattered to the side) and a sunset is red (the light that goes straight through the sky).

Why are Eyes Different Colors?

Our skin, hair, and eyes come in many different colors. Amazingly all those different colors are made from exactly the same stuff! That stuff is a pigment, or colored material, called melanin.

The color of our hair and skin is mainly caused by the amount of melanin there (and the underlying blood and body tissue for our skin color). The more melanin present, the darker our hair or skin. Black hair has lots of melanin. Blonde hair has a little bit. And gray hair has none at all.

The same is true for eyes. The amount of melanin in our irises (the colored part of the eye) helps determine its color. But since melanin itself is black or very dark brown, how can we get blue eyes? Eye colors like blue and green are produced by small amounts of melanin in our eyes in the form of very small particles that scatter light, just like small particles in the sky scatter light to make it look blue (or the milk in water shown in the picture above). It is also interesting to note that the pattern in our iris (the colored part of the eye) is considered absolutely unique. The chances of finding a person with an identical iris are so low, that you would have to check far more people than are currently living on Earth to find one!

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Ever wonder ... What does the world look like to color blind people?


Updated: Jan. 24, 2010