Infrared waves

Infrared waves were discovered by William Herschel in 1800. Every hot body emits infrared radiation, and it is a major component of the Sun's output -- about 60% of all solar radiation reaching the Earth is infrared. Because infrared cannot be seen or photographed with an ordinary detector as easily as visible light, specialised instruments such as thermocouples, thermopiles and bolometers are used to detect it, all of which work by sensing the heating effect the radiation produces.

That heating effect is in fact the defining property of infrared waves: when infrared radiation is incident on any object, the object gets heated. Infrared is strongly absorbed by ordinary glass, but -- usefully -- it can penetrate through thick columns of fog, mist and cloud cover that would block visible light, which underlies several of its applications. Uses include remote sensing, diagnosis of superficial tumours and varicose veins, therapeutic treatment of infantile paralysis, sprains, dislocations and fractures, solar water heaters and solar cookers, thermography (special infrared photographs called thermograms can reveal diseased organs, because diseased tissue typically radiates less heat …