Infrared Spectrum

The infrared spectrum, derived from the Latin word “infra,” meaning “below,” refers to the section of the electromagnetic spectrum that has longer wavelengths than visible red light. This versatile range spans a wide array of wavelengths, enabling a diverse range of applications including night vision, temperature sensing, and material composition analysis.

Infrared Spectrum Imaging Bands

Generally, the infrared spectrum consists of four defined imaging bands, each with its own unique characteristics and applications.

1. Near Infrared (NIR): Ranging from approximately 0.75µm to 1.5µm, NIR is used in surveillance, remote sensing, and medical imaging
2. Short-Wave Infrared (SWIR): Spans from about 1.0µm to 2.5µm. SWIR is useful in industrial inspections, agriculture, and maritime surveillance due to its ability to see reflected light through fog. (There is some overlap between NIR and SWIR, with distinctions made between them due to differences in applications and sometimes in detector materials.)
3. Mid-Wave Infrared (MWIR): Spanning 3.0µm to 5.0µm, MWIR is crucial for thermal imaging, gas detection, and defense, often requiring cooling to operate effectively.
4. Long-Wave Infrared (LWIR): Covering 7.5µm to 14µm, LWIR excels in building diagnostics, electrical inspections, and surveillance by detecting heat signatures even in total darkness. Some LWIR systems operate without cooling, making them more affordable.

Thermal Imaging vs. Infrared Imaging

Infrared and thermal imaging are not necessarily the same thing. While an imager that operates on wavelengths longer than about 750nm can be considered an infrared imager, thermal imagers only operate in the MWIR or LWIR bands. While all objects emit some amount of thermal energy, most common objects such as people, vehicles, and background objects emit detectable energy only in the MWIR or LWIR bands; therefore those bands are used for thermal imagers. Objects that are extremely hot will begin to emit detectable amounts of energy at shorter wavelengths; the hotter the object, the shorter the wavelengths that it will emit at. This is illustrated by the common example of a piece of iron or steel that is left in a fire for an extended period; it will get hot enough to glow (emit light) even in the relatively short visible wavelengths.

Applications of the Infrared Spectrum

From detecting chemical compounds using NIR to spotting hidden heat sources with LWIR, infrared imaging enhances various industries by offering unique insights into the world, from industrial inspection to security solutions.