Wavelength: 7 x 10-7 - 1 x 10-3 m
Frequency: 3 x 1011 - 4 x 1014 Hz
Energy: 2 x 10-24- 2 x 10-22 eV
Infrared (IR) is the closest to visible light we’ll get to on this end of the spectrum. At it’s shortest wavelength it is just bordering on what we can see with the naked eye. The IR radiation can be broken up further into the following spectrum:
Near Infrared: 0.7µm - 1.3µm wavelength
Short Infrared: 1.4µm – 3µm wavelength
Mid Infrared: 3µm - 8 µm wavelength
Long/Thermal Infrared: 8µm - 30µm
Far Infrared: 15µm – 1000µm
Astronomers divide the spectrum differently, usually as follows :
Near IR: 0.7 µm – 5 µm
Mid IR: 5 µm – 40 µm
Far IR: 40 µm – 350 µm
Mid Infrared and Long Infrared are emitted by an object naturally, while Near Infrared and Short Infrared are reflected off an object.
IR was first theorized by Emilie du Chatelet in 1737 in a paper titled Dissertation sur la nature et la propagation du feu. Her theory was proved correct in 1800 when William Herschel published the first record of experimental proof of IR radiation.
The most common type of IR radiation that you or I would recognize is heat. IR radiation from the Sun provides Earth with 49%  of its heat, with thanks to greenhouse gases. Without any of those, no IR heat would be absorbed and slowly released back into our lower atmosphere to keep us at our cozy temperature.
Without IR radiation, we wouldn’t be able to use nightvision technology. Both traditional nightvision and thermal imagine use light in the IR spectrum to enhance images in otherwise dark areas. The absorption of IR into clouds and the atmosphere allow our weather satellites to make mostly accurate weather predictions that you end up seeing on the nightly news. In astronomy, IR can be used to measure through clouds of molecules, nebulae, and detect redshifted objects .
Blackbody radiation is the natural amount and type of electromagnetic radiation that an object absorbs at any given temperature above absolute zero. At Earthly temperatures, blackbody radiation exists in the IR range , as that is the only range on the spectrum that it won’t absorb entirely.
Some animals have evolved natural mechanisms that allow them to detect IR light. These animals include pit vipers, pythons, some boas, vampire bats, and some insects. It is unknown the degree to which these animals can sense IR light, but there’s no doubt that it must help them hunt prey or avoid predators!
Passive Solar Heating & Cooling Manual. Rodale Press, Inc.. 1980. Retrieved 2007-08-12