Just below the visible spectrum is infrared (IR) radiation. These are longer wavelength light rays (about 1.00 mm to 8 x 10-7
m, or 80,000 Ångströms) with energies between 10-3
eV and 1 eV.
Many molecules tend to resonate or vibrate easily when exposed to IR radiation, so we erroneously think of IR as heat waves. The sun emits about half of its radiation in the IR and light bulbs emit more IR than visible light. Many devices use IR as a means of transmitting information (IR lasers, TV remote controls) and receiving signals (IR telescopes, photographic films, satellites). In order to "see" at night, IR goggles pick up the infrared radiation from our warm bodies, translating the signal into visible light that our eyes can detect.
Astronomers use IR telescopes to see inside and beyond huge clouds of gas and dust that block our (visible light) view of such places as the center of the Galaxy. Art preservationists use IR cameras to view paintings that might have underdrawings not visible to the human eye. Charcoal absorbs IR quite well, but most pigments of paint are transparent to infrared. If one shines an IR light on a painting with an underdrawing made of charcoal, the paint layers will pass the radiation, the charcoal will absorb the IR, and the camera will see the white background that reflected the radiation with dark areas corresponding to the drawing made with a charcoal pencil.
This picture is made with a infraredcamera and is called a thermogram. The man is only lighten by infrared radiation. The hottest parts are colored brightst (yellow).
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