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## What is Color?

by Nancy Sutthoff

### The Electromagnetic Spectrum

The entire electromagnetic spectrum is made up of ultraviolet, visible light, and infrared. The human eye can only see the light sector of the spectrum. That is Red, Orange, Yellow, Green, Blue, Indigo and Violet. (ROY G BIV is how I was taught to remember it in school). These are also the colors you see in a rainbow after a rainstorm.

### Visible Color

Color is the thing we perhaps notice most about light in the world around us. But why we see colors the way we do all has to do with light. The reason something appears to be the color that does is that the object is absorbing all the other colors of light except the ones we see, which are reflected back to our eyes. If something absorbs all the colors, it appears black, if it reflects everything, it appears white. Color comes from what is called the visible spectrum of light. Scientists measure the wavelengths of light in this spectrum in nanometers or billionths of a meter. Red has the longest wavelength, and violet has the shortest. So, what color we see depends on the wavelength of the light we absorb into our eyes. The primary colors are red, green, and blue, from these colors, every other color can be made.

### Invisible Color

The ultraviolet and infrared are wave energy that can not be seen by our eyes. William Herschel began down the road to discovering the electromagnetic spectrum in 1799. He wanted to find out how light and heat were connected. He used a prism to break up white light and used a thermometer to measure the temperature of each of the different colors. Each color, he found, did not have the same temperature. Red had the highest reading of all of the colors, while violet gave the lowest.

### Infrared

However, past the red that we are able to see, Herschel found something that was even hotter than red itself. This end of the electromagnetic spectrum he called infrared. Infrared can be felt, but it can not be seen by the naked eye. The wavelengths of the visible spectrum are all medium in length. The wavelengths of infrared light are very slow. Everything emits infrared light. Even things found in your freezer emit it. Infrared can be found in anything above absolute zero. The amount of infrared light that an object emits depends on its temperature. A human gives off much more infrared light than an ice cube would. No matter what time of day it is, the same amount of infrared light is given off. Because of this, movement can be detected in the dark with infrared detectors. Some animals, like snakes of the pit viper family, are able to pick up on infrared waves to detect their prey.

### Ultra violet

At the other end of the spectrum, past violet, is ultraviolet. Ultraviolet was discovered by Wilhelm Ritter in 1801. He dipped strips of paper into silver nitrate and shown certain types of light on them. Silver nitrate goes under a chemical reaction when exposed to light, and Ritter found that the reaction was different depending on the type of color that was shined on it. When exposed to violet light, the paper would turn much darker than any of the other colors. Knowing that Herschel had found unseen light at the red end of the spectrum, Ritter decided to see if there was at the violet end. When he did this, the paper turned darker than when exposed to violet light, proving that there was light beyond violet. This invisible light was named ultraviolet. Ultra violet light is often given off by the sun. Most are reflected by the ozone layer, but some do get into our atmosphere. These rays damage unprotected skin and have been known to cause skin cancer. This is the light that gives you sunburn and this is the light that sunscreen protects us from.

Just as with Light, Color is not as simple as it seems to be at first thought. To find out more about color, take a click over to the website listed below:

Color Matters  how color affects us all