The basic principle of night vision
To understand the principle of night vision devices, you must understand the principle of light. The energy of a light wave is related to its wavelength: the shorter the wavelength, the higher the energy. Among visible light, violet light has the highest energy, while red light has the lowest energy. Adjacent to the visible light spectrum is the infrared spectrum. Infrared rays are divided into three categories:
Near Infrared (near IR) - near infrared is adjacent to visible light, and its wavelength range is 0.7-1.3 microns (1 micron is equal to one millionth of a meter).
Mid-Infrared Rays (Middle IR) - The wavelength range of mid-infrared rays is 1.3-3 microns. Near-infrared rays and mid-infrared rays are used in various electronic devices such as remote controls.
Thermal Infrared Rays (Thermal IR) - Thermal infrared rays occupy the largest part of the infrared spectrum, with wavelengths in the 3-30 micron range.
The main difference between thermal infrared and the other two types of infrared is that thermal infrared is emitted by objects rather than reflected from them. Objects are able to emit infrared light because of certain changes in their atoms.
