Infrared is a type of light that we cannot see with our eyes. Our eyes can only see what we call visible light. Infrared light brings us special information that we do not get from visible light. It shows us how much heat something has and gives us information about an object's temperature. Everything has some heat and puts out infrared light. Even things that we think of as being very cold, like an ice cube, put out some heat. Cold objects just put out less heat than warm objects. The warmer something is the more heat it puts out and the colder something is the less heat it puts out. Hot objects glow more brightly in the infrared because they put out more heat and more infrared light. Cold objects put out less heat or infrared light and appear less bright in the infrared. Anything which has a temperature puts out heat or infrared light. In the infrared images shown below, different colors are used to represent different temperatures. You can find out which temperature a color represents by using the color-temperature scale show to the right of most of the images. The temperatures are in degrees Fahrenheit.

To the left is an infrared image of a metal cup holding a very hot drink. Notice the rings of color showing heat traveling from the liquid through the metal cup. You can see this in the metal spoon as well. To the right is an infrared image of a melting ice cube. Notice the rings of color showing how the melt water warms as it travels away from the cube. Although the ice cube is cold, it still puts out heat, as you can see by matching the color of the ice cube with its temperature.

A visible light picture (left) and an infrared picture (right) of two cups. One cup contains cold water, while the other contains hot water. In the visible light picture we cannot tell, just by looking, which cup is holding cold water and which is holding hot water. In the infrared image, we can clearly "see" the glow from the hot water in the cup to the left and the dark, colder water in the cup to the right. If we had infrared eyes, we could tell if an object was hot or cold without having to touch it.

By using special infrared cameras, we can get a view of the infrared world. These cameras are very useful and have even helped save people's lives. In the infrared, you can "see" in the dark. Even if the Sun is down and the lights are off, the world around us still puts out some heat. The infrared picture to the right shows deer in a forest during a dark night. Notice how we can clearly see the heat from the deer, especially from areas not covered with thick fur like the ears, face and legs. The trees and the ground put out less heat than the deer, but can still be seen through an infrared camera.

Warm-blooded animals, like people, try to keep the same body temperature during both the day and the night. Their body temperatures do not change when it gets dark or cold outside and their heat remains about the same. This makes infrared cameras very useful for finding people who are lost at night or lost at sea. The warm body heat from a person will cause them to glow brightly in the infrared, even in the dark or floating in a cold sea. Police can use infrared cameras to find criminals hiding in the dark and firefighters also use infrared cameras to find the hot spots in a fire.
Black and white infrared image of a person lost at sea at night. Notice how this person glowed in the infrared even when he could not be seen in visible light.

Infrared cameras are also a good way to study warm-blooded animals at night, and are used to study how animals use fur, feathers and blubber to keep themselves warm. They are also useful for showing the difference between warm and cold-blooded animals. To learn more about warm and cold-blooded animals visit our The Infrared Zoo website.

Above are infrared images of a warm-blooded dog (left) and of a warm-blooded human holding a cold-blooded caterpillar (right). Warm-blooded animals, like the dog shown above, make their own heat. In the infrared picture you can see how the dog's fur keeps some of this heat from escaping, keeping the dog warm. Insects are cold-blooded, which means that they cannot make their own body heat. Instead they take on the temperature of their surroundings. The cold-blooded caterpillar appears very dark (cool) in the infrared compared to the warm-blooded human who is holding it. Notice how the caterpillar is at about the same temperature as the surrounding air.
Another interesting fact about infrared light is that it can travel through thick smoke, dust or fog, and even some materials.

Above is a visible (left) and infrared (right) view of a person's hand inside a black plastic bag. In the visible image, the hand cannot be seen. In the infrared image, however, the heat from the hand can travel through the bag and can be seen by an infrared camera. Infrared light can pass through many materials which visible light cannot pass through. However, the reverse is also true. There are some materials which can pass visible light but not infrared. Notice the man's glasses! Infrared cannot travel through glass. Since this man's body heat cannot travel through his glasses, they appear dark.
Because infrared light can travel through thick smoke and visible light cannot, infrared cameras are used by firefighters to find people and animals in smoke filled buildings. The infrared body heat from people and warm-blooded animals can travel through the smoke and cause them to show up clearly through an infrared camera. Many people and their pets have been saved by firefighters using infrared cameras. Also, because infrared light can travel through thick fog, it is very useful to have infrared cameras on ships and airplanes to help in navigation.

To the left is a black and white infrared image showing a person trapped in thick smoke. Firefighters using infrared cameras could find and rescue this person. The image to the right shows the visible and infrared views from an airplane as it tries to land in thick fog. In visible light, the runway cannot be seen. An infrared view, however, allows the pilot to see the runway and land safely.
Infrared cameras are also used by satellites in space to measure the temperature of the oceans, to study the Earth's weather during both the day and night, and to study the infrared light from outer space.

To the left is an infrared map of sea surface temperatures, with red being the warmest and purple the coldest. To the right are two images taken by telescopes of a thick area of gas and dust in space where stars are born. Since infrared can travel through thick dust, astronomers can see through thick clouds of dust and gas in space by using infrared telescopes. On the left is a space cloud as seen by a visible light telescope. Notice that we cannot see what lies behind the cloud. In the infrared view (right) we can see through the cloud and find bright, young stars which have just been formed.
There are many other valuable things that we can learn by viewing the world in the infrared. To learn more about this visit our web site "Seeing Our World in a Different Light". It is written for ages 14 and up, so if you have any trouble understanding the text; ask your parents, guardians, or teachers to go over this site with you.
Infrared light is only one of the types of light that we cannot see with our eyes. There are many more, such as X-rays, gamma-rays, ultraviolet light and radio waves. Each of these different types of light bring us new information that we cannot get by using our eyes alone. We are very lucky that we live in a time when we have technology that allows us to "see" all of these types of light.

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