Infrared is defined in range between 780 nm and 1 mm (which are 1,000,000 nm).
One of the spectral classification based on the types of molecular vibrations, focusing on the impact of applications. The terms are not as clear as in the visible range and are defined partly by the applications or special physical phenomena determine why there are several different names.

• Near-infrared – short wave infrared (near infrared, NIR): short wave IR radiation which directly joins to the visible (red) area followed by 780 nm to 1400 nm.
• Medium infrared – mid wave infrared (mid-infrared, MIR) joins at wavelengths from 3 microns to 50 microns.
• Far infrared - long wave infrared (far infrared, FIR) is longwave infrared radiation from 50 microns to 1 mm and adjacent to the field of Terahertz.