Sir William Herschel discovered infrared radiation in 1800. He conducted an experiment using a glass prism to split sunlight and found that the mercury in a thermometer rose higher just beyond the visible red light. This discovery proved that invisible radiation existed beyond the visible spectrum and carried energy that could be felt as heat.
The infrared band stretches from 700 nanometers to 1 millimeter. This range occupies a vast territory between visible light and microwaves that remains hidden from human perception. Within this range, scientists have identified distinct subdivisions such as the near-infrared region extending from 0.75 to 1.4 micrometers.
The Zielgerät 1229 Vampir system was the first portable infrared device for military applications. Introduced in 1945, it allowed soldiers to see in darkness by detecting the infrared radiation emitted by human bodies. This system marked a transformation of infrared science into a weapon of war during the 1940s.
Infrared observatories are typically located at high altitudes such as the Infrared Telescope Facility on Mauna Kea. They are also placed aboard aircraft and balloons to rise above the moisture that absorbs incoming radiation. Space telescopes using liquid helium-cooled detectors provide the clearest view free from atmospheric interference.
Infrared reflectography helps art conservators reveal hidden layers beneath famous paintings by capturing images in the near-infrared and short-wavelength infrared regions. This technique allows them to see underdrawings and pentimenti that are invisible to the naked eye. It has uncovered portraits of men beneath Picasso's Woman Ironing and Blue Room and examined ancient documents like the Dead Sea Scrolls.
Pit vipers and pythons use infrared-sensitive pits on their heads to identify and capture warm-blooded prey. The common vampire bat relies on thermoreceptors to locate blood-rich regions on its victims. The jewel beetle Melanophila acuminata locates forest fires via infrared pit organs to deposit its eggs on recently burnt trees.