Infrared (IR) is invisible radiant energy, electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at ~700nm (frequency 430 THz) to 1mm (300 GHz) (although from test data some people can see infrared up to at least 1050nm) in λP wavelengths. Often times what we call Near IR is added to this range at the low end to encompass 665nm and upwards wavelengths. Much of the energy from the Sun arrives on Earth in the form of infrared radiation. Sunlight at zenith provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation. IR radiation is often divided into three smaller regions: 0.750 – 3μm, 3 – 30μm, and 30 – 1000μm – defined as near-infrared (NIR), mid-wave infrared (MWIR), and far-infrared (FIR), respectively. The CIE IR band divisions include IR-A, -B and –C.

IR-A 700nm–1400nm (0-7μm – 1.4μm)
IR-B 1400nm–3000 nm (1.4μm – 3μm)
IR-C 3000nm–1mm (3μm – 1000μm)

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