Infrared rays can indeed be subdivided into three parts: near-infrared, mid-infrared and far-infrared, each of which has different wavelengths and application characteristics. Near-infrared wavelengths range from 0.75-1 to 2.5-3 microns, and it can penetrate human tissues to a depth of about 5-10 millimeters; in contrast, far-infrared rays, the portion with wavelengths between 25-40 and 1,500 microns, are more absorbed by the surface layer of the skin and penetrate to a depth of less than 2 millimeters.
Near-infrared rays are commonly used in the medical field because of their short-wave nature, such as in skin treatments to provide deep heat therapy. Far infrared, on the other hand, plays a role in nighttime surveillance equipment such as night vision devices, where its passive design is not easily detected, and also has the ability to penetrate environments such as fog and rain. In addition, infrared rays have applications in daily life, such as infrared filters in see-through telescopes, which not only enhance nighttime observation, but also allow you to see objects through clothing; in cooking equipment such as light-wave ovens, the light-wave tube technology used can quickly generate high temperatures, cooking food better, and can maintain the color of the food.
In summary, these three parts of infrared light are not only distinguished by their wavelengths, but each plays a unique role in technology and life. Understanding these wavelengths and properties helps us better understand their specific applications in different fields.