What is Infrared?
Infrared is radiation from the part of the electromagnetic spectrum that is just beyond human visual capabilities. Visual light is actually a very narrow band in the electromagnetic spectrum with a wavelength range of 0.4 – 0.7 microns. Just beyond the violet end of the visible light spectrum is ultraviolet radiation (0.01 – 0.4 microns). Just beyond the red end of visible light is Infrared (0.7 – 30 microns). Just beyond the infrared spectrum are microwaves.
All objects above absolute zero temperature emit radiation from their surface in a spectrum of different wavelengths and intensities. The principle wavelengths emitted and their intensity depend on the absolute temperature of the object. As the temperature of an object rises, the amount of radiation emitted rises proportionally and the spectrum of radiation broadens to include shorter wavelengths. The peak will move from the long wavelength end of the infrared spectrum toward the shorter end as the temperature increases. At about 930°F, objects will begin to emit visible light radiation in addition to IR; giving off a deep red glow. At 7000°F, the radiation intensity is highest in the visible light region.
Because IR is not visually detectable, it must be converted to another form of energy that can be more easily manipulated. Typical conversion detectors are thermocouples, thermometers and photodetectors. Photodetectors have formed the basis for most of the work done in the IR field in the last 75 years. Today’s thermal detection instruments fall into two broad categories: thermal measurement and thermal imaging.