The spectral range describes the area of the electromagnetic spectrum in which a certain type of radiation occurs. It ranges from electromagnetic waves with very short wavelengths, such as X-rays, to very long wavelengths, such as radio waves. The term is used to distinguish and categorize the different types of electromagnetic radiation.

In optics, the spectral range is used to describe the spectrum of visible light. Visible light consists of electromagnetic waves with wavelengths between 400 and 780 nanometers. These wavelengths are perceived by our eyes and appear to us as different colors.
The spectrum of visible light can be divided into different color ranges, from violet to blue, green, yellow, orange and red. Each of these color ranges has a specific wavelength and frequency.
Beyond the visible spectrum, there are many other types of electromagnetic radiation. Ultraviolet radiation, X-rays and gamma radiation have a much shorter wavelength than visible light and are invisible to the human eye.

The ultraviolet and infrared range comprises wavelength ranges above and below the visible range. The ultraviolet range extends from around 10 nm to 400 nm, while the infrared range extends from around 700 nm to several micrometers.

The spectral range of infrared pyrometers in practice
Infrared pyrometers for non-contact temperature measurement can operate in different spectral ranges, depending on the requirements of the application. The most important spectral ranges are the short-wave infrared range (SWIR), the medium-wave infrared range (MWIR) and the long-wave infrared range (LWIR).

The SWIR range covers wavelengths between 1 µm and 3 µm. This range is well suited for non-contact temperature measurement of metals and semiconductors, as these materials have a high absorption in this range. Pyrometers for this wavelength range are therefore often used in the steel industry, in semiconductor production and in the electronics industry.

The MWIR range covers wavelengths between 3 µm and 5 µm and can therefore be used well for non-contact temperature measurement of materials such as plastics and organic materials, as these materials have a high absorption in this range. This range is therefore often used in the plastics industry, the food industry and the pharmaceutical industry.

The LWIR range covers wavelengths between 8 µm and 14 µm. This range is well suited for non-contact temperature measurement of materials such as ceramics, non-metals, fabric, paper and asphalt, as these materials have a high absorption in this range.

The choice of the correct spectral range depends on various factors, such as the type of material to be measured, the surface properties of the object to be measured, the desired measurement accuracy and the distance between the object to be measured and the infrared pyrometer.