by 
The Curious Bag
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Infrared light is a type of radiation used in cameras, satellites and remote controls among its many applications. To the unaided human eye, infrared light is invisible. Its invisibility comes from its relatively long wavelengths, which fall outside of the visible spectrum.
History
Around 1800, astronomer William Herschel discovered infrared light. Herschel had detected heat below the red band of visible light, and the term infrared, fittingly, means "below red."
Size
In terms of wavelength, infrared measures between 0.7 and 300 microns (1 micron is one-millionth of a meter). Visible light, in contrast, measures between 0.4 and 0.7 microns.
Sources
Infrared light comes from any source of heat, ranging from the sun to an ice cube (heat, of course, being a relative term in science). The hotter an object, the more infrared light it emits.
Applications
Infrared light has a wide variety of applications. For example, infrared light sends information, such as for a remote control. It detects heat, thus can be used in night vision by the military. In addition, it allows astronomers to see past clouds of gas and dust in space.
Fun Fact
Because they produce heat, humans are themselves a source of infrared light. According to NASA (2007), most infrared light emitted by humans measures 10 microns in wavelength.
Source:
NASA.gov: The Electromagnetic Spectrum
ReachOutMichigan.org: Infrared Light
Gemini.edu: Infrared Radiation--Warmth from the Cold of Space
More Information:
Kirtland Air Force Base: Space-Based Infrared Technology Center of Excellence
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