Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light. IR is generally invisible to human eyes, although some people with a medical condition known as retinitis pigmentosa can experience IR as flickering lights.1
The name “infrared” comes from the Latin word infra, meaning “below”.2 Red is the color of visible light with the longest wavelength, so “infrared” means ” below red” – that is, below the red end of the visible spectrum.3 Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers (nm)4 to 1 millimeter (mm).5 This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz.6 Most thermal radiation emitted by objects near room temperature is infrared.7
As thermal radiation consists mostly of infrared radiation,8 sky glow from cities and industrial areas also contains a large percentage of infrared light.9
IR can also be produced artificially using electric currents or lasers;10 it has many applications in science and technology, including night vision11 and remote control12 for devices such as televisions and garage door openers.13 In medicine,14 it is used in handheld devices15 for diagnosis16 and treatment17 of various conditions such as carpal tunnel syndrome18 and arthritis.19 It is also used in certain types20 of cancer treatment21 and wound healing22 therapies.23
Most man-made objects emit some infrared Radiation;24 this includes both natural sources like humans25 and hot objects like engines or sun-baked asphalt pavement. The intensity depends on temperature: very hot objects may emit intense levels while cooler ones will emit less so that even cold objects like ice cubes can be detected by their infrared emission.26 The Sun emits large amounts of black-body radiation across the entire electromagnetic spectrum; most notably in the form of visible light but also ultraviolet light, X-rays and radio waves as well as all frequencies in between those extremes including all frequencies within the infrared portion of sunlight’s total output power per unit area per unit wavelength interval peak near 10 micrometers which places them squarely within what people would call ‘the far-infrared’ region..27 28 All these components together are what we experience as sunlight..29 30