Your skin is an excellent detector of infrared (IR) radiation. When you step outdoors into the sun, you "feel" the of heat the sun. Your skin is responding to the infrared radiation from the sun that you cannot detect with your eyes.

Your skin is also an excellent infrared radiator! You can detect your own infrared radiation by placing a liquid crystal panel close to your skin and and observing its color change after a few minutes. Each strip changes color with a change in temperature. These liquid crystal strips are responding to infrared radiation at ambient temperatures. They are also sold as thermometers, with a typical range of about 65 degrees to 85 degrees Fahrenheit.

Try the "Liquid Crystal IR Detector" activity. Click on the graphic to begin.  Liquid Crystal IR Detector

Take a look at these infrared and visible light photographs.
  Here are two pictures of Neil Fetter. One is obviously visible light. The other is an infrared image.

The camera used to take the IR photo was kept at the temperature of liquid nitrogen (-196 degrees Celsius). The coldest part of the face is the nose and the background is so cold, it is not detected by the IR camera.

Liquid crystal panels are inexpensive and available from most scientific equipment suppliers and from the Exploratorium Store.

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