Infrared Light
Written by John Carl Villanueva
Infrared (IR) light is part of the electromagnetic wave spectrum that borders the lowest frequency/longest wavelength among those that make up visible light. Just like all members of the electromagnetic wave spectrum, the IR frequencies overlap with its adjacent members. However, most of IR is between 750 nm and 1,000,000 nm.
Infrared radiation is what is emitted by a warm or hot body and is where the term 'red hot' was derived from.
Optical infrared radiation is divided into three bands by the International Commission on Illumination:
IR-A for wavelengths between 700 nm and 1,400 nm – Some applications include fiber optic communication and night vision goggles.
IR-B for wavelengths between 1,400 nm and 3,000 nm – This band is most noted for its application in long-distance telecommunications.
IR-C for wavelengths between 3,000 nm and 1,000,000 nm – Typically used in the military, specifically in 'heat seeking' missiles as well as in thermal imaging.
Astronomers typically make use of practically all three bands to observe a wide variety of temperature ranges.
Some Applications of Infrared Light
Night Vision
Night vision devices make use of infrared by either capturing the naturally emitted IR from the subjects or by using infrared light sources that are not as noticeable as visible light. Devices like these are mostly used in the military.
Thermal imaging
Devices that make use of thermal images are able to display outlines of the subjects based on the amount of infrared radiation (which corresponds to the amount of heat) emitted by the body. Applications range from medical diagnostic to search and rescue devices. These are highly favored devices because of their non-invasive capabilities.
Communications
You're probably most familiar with this than other applications. Before the introduction of Bluetooth, IR was the dominant wireless means of transferring data between two mobile devices or between mobile devices and a computer. This method required line-of-sight and was only possible at short distance separations (a few centimeters).
Astronomy
Infrared telescopes are pretty much like ordinary telescopes such that they make use of components like mirrors and lenses in addition to digital detectors. To avoid the interference of water vapor found in the atmosphere, most of these telescopes are placed at very high altitudes.
There are many advantages of infrared telescopes over those that rely on visible light. One of them is the better penetration capability of IR. Infrared telescopes can either be used to detect the IR that are emitted by the celestial bodies themselves or the IR that is bounced off a cooler celestial body from a nearby star.
You can read more about infrared light here in Universe Today. Want to know how a balloon experiment solved the mystery of far infrared background? We've also written about the crucial role played by infrared in explaining why galaxies are smooth.
There are also interesting stories from NASA and PhysicsWorld:
NASA Infrared Images May Provide Clues About Mt. St. Helens' Eruption
High Performance Near Infrared Camera
Here are two episodes at Astronomy Cast that you might want to check out as well:
Infrared Astronomy
Optical Astronomy
Filed under: Astronomy
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