"Infrared (IR) light is electromagnetic radiation with longer wavelengths than
those of visible light, extending from the nominal red edge of the visible spectrum at 0.74 micrometres (µm) to 300 µm. This range of wavelengths corresponds to a frequency range of approximately 1 to 400 THz,[1] and includes most of the thermal radiation emitted by objects near room temperature. IR light is emitted or absorbed by molecules when they change their rotational-vibrational movements. The existence of IR radiation was first discovered in 1800 by astronomer William Herschel."
"Much of the energy from the Sun arrives on Earth in the form of IR radiation. Sunlight at zenith provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is IR radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation.[2] The balance between absorbed and emitted IR radiation has a critical effect on the Earth's climate."
"IR light is used in industrial, scientific, and medical applications. Night-vision devices using IR illumination allow people or animals to be observed without the observer being detected. In astronomy, imaging at IR wavelengths allows observation of objects obscured by interstellar dust. IR imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatus."