Infrared radiation is a spectrum of electromagnetic radiation that falls between the red end of visible light and microwave radiation. It makes up the bulk of the thermal radiation of bodies (especially bodies with temperatures above 500 K), as well as almost all radiation observed in nature (except for radiation absorbed in the atmosphere). Only about 0.01% of the light emitted by the Sun comes from the infrared region!
The infrared region is also called the region of “warm” rays, “invisible” radiation. The fact is that human eyes are capable of seeing only part of the infrared spectrum, from 0.7 to 1 millimicron, i.e. where the eye no longer sees red, but yellow. Long-wave infrared rays in the visible region are generally invisible to human eyes. That is why they are called “infrared”, from the Latin word infra (below) and the Latin word red.
Long wavelengths have low energy and therefore cannot cause optical changes in matter. However, they are well absorbed, since they correspond to a certain visible wavelength range, but at the same time they are reflected very well. Just like the reflection of visible radiation and visible electric rays, infrared radiation can be used to detect various objects or materials.