What is infrared light and how does it work?

How do we detect infrared light? How is it produced and how does it compare with visible light? What are some of the technologies that take advantage of infrared radiation?

                                                    David uncovers exciting 
                                                    technological advances that 
                                                    use infrared light.


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When we talk about infrared radiation, we're really talking about a particular kind of light. If you combine infrared radiation with radio waves, microwaves, visible light, ultraviolet radiation, X rays, and gamma rays, you'll end up with a broad band of radiation frequencies called the electromagnetic spectrum. All of these types of electromagnetic radiation transfer energy through space via waves of oscillating electromagnetic fields. What distinguishes them from each other are the frequency of the oscillation and, consequently, the wavelength.

An object's molecules and electrons are always in motion, vibrating and radiating electromagnetic waves. When the object heats up and its temperature increases, the motion will increase and so will the average wave frequency and the intensity of the radiation. You can see this at work in a toaster oven. When you turn the toaster on, you can feel some heat, but you see no light. As more electric energy is supplied and the wires get hotter, they begin to glow red. If you could really turn up the power so that the temperature reached about 3,000*C, the wires, like the filament in a light bulb, would glow white. The only problem is that they would probably burn up before they reached that temperature.

British astronomer Sir William Herschel discovered infrared radiation around 1800. He used a prism and a sensitive thermometer to detect "invisible" light found just below the red portion of the spectrum. The term infrared (meaning "below red") came into use because it describes where you find it on the electromagnetic frequency spectrum.

Any warm object gives off infrared radiation. But remember, warm is a relative term. An ice cube in a cooler is warmer than a flask of liquid nitrogen, so it gives off more infrared radiation. Using special infrared scanners, a thermographic scanner takes these differences in radiation intensity, codes them by color, and maps them out so that "hot spots" can be detected. With this technology, engineers can find heat leaks in buildings, doctors can find hidden tumors in the body, and biologists can even find diseased vegetation in a forest.

Infrared imaging can even have applications in space. Astronomers use infrared imaging to detect warm dust around new stars not "hot" enough to give off visible light. This gives them a more complete picture of the whole universe, seeing where no one has seen before!


  1. Rattlesnakes and other reptiles can perceive infrared radiation. Does that mean they can see in the dark?
  2. If you could only see in the infrared range, which would "light up" your life more--an electric iron or a fluorescent light?


Additional sources of information

Community resources


You will discover how infrared radiation behaves compared to visible light.


Most television remote control units work by means of infrared radiation rather than visible light. That's why you can't see the beam go on when you change channels. Because infrared radiation has a longer wavelength than visible light, it behaves differently when it encounters objects that get in its way.

Using your television's remote control as a source of infrared radiation, you will compare the behavior of a beam of infrared radiation to that of a beam of visible light. You will see how each reacts when different materials are placed in its path.


  1. Clear all obstructions between you and the television set. Darken the room as much as possible. Stand about 3 meters (10') away from the set and test your remote control unit to make sure it is functioning properly. Test your flashlight by shining it against the dark television screen.
  2. Have a friend stand about halfway between you and the television, directly in front of the screen. Try turning on the television using the remote control. Then try shining the flashlight onto the television screen. Observe what happens in each trial. Have your friend move around and notice how both "light" beams behave.
  3. Have your friend blow some cornstarch baby powder in the air between you and the television and attempt to turn on the television through the dust. Repeat, using the flashlight, and observe what happens when you aim it at the screen.
  4. Place the glass of water directly in front of the remote control unit and try to turn on the television. Now shine the flashlight through it. Note what happens in each case.
  5. Hold the remote control in your right hand and place your left hand at several distances and angles relative to the remote control. Determine the conditions under which your hand motion prevents the signal from reaching the television.


  1. Which of the objects interfered with the flashlight beam? Which stopped the infrared beam?
  2. Why do you think infrared sensors are good at detecting hot spots in forest fires, yet have problems detecting warm bodies in the fog?
  3. How does the longer wavelength of infrared radiation help to explain your observations?

Kodak has developed infrared film that works in a standard 35-mm camera. This type of film can often be purchased at a well-stocked photography supply store. You can set up a test experiment by selecting several different targets and photographing them in both infrared and visible light. You'll be amazed at what develops!

Go into a dark room that has an incandescent light bulb controlled by a dimmer switch. Observe the spectrum it produces through a diffraction grating when the light is fully turned on. (See resources for diffraction gratings.) Slowly turn the dimmer switch down while observing through the grating. What happens to the spectrum? What connection does this have to infrared radiation?

For over 10 years, NASA has photographed Earth in the infrared range from satellites to measure long-term environmental changes. Contact NASA (see resources) to obtain LANDSAT infrared images of your community and see how the different "heat" colors show the commercial and residential developmental pattern.

Radiometers--those things that look like light bulbs with a weather vane inside--not only measure the intensity of visible light but react to infrared as well. Conduct an infrared survey by placing the radiometer near a variety of warm objects to see which has the most effect. The faster the "weather vane" spins, the more intense the radiation. (See resources for radiometers.)

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