As infrared radiation ( IR radiation short, even Ultrarotstrahlung ) is referred to in physics electromagnetic waves in the spectral region between visible light and the longer wavelength of the terahertz radiation. As the infrared spectral range between 10-3 m and 7.8 x 10-7 m is designated (1 mm and 780 nm ), which is a frequency range of 3 x 1011 Hz to about 4 x 1014 Hz ( 300 GHz to 400 THz) corresponds.

Classification of the spectral range

A classification of the infrared spectral range is based on the types of molecular vibrations, which affect the applications. The terms are not defined clearly as in the visible range and applications or specific physical phenomena are partly determined, which is why there are several different names by. The International Commission on Illumination (CIE ) and DIN beat the division into three bands before: IR -A, IR -B and IR-C (MIR and FIR).

  • Short-wave part of the NIR range, 780 -nm limit due to the solar spectrum matched the human sense of sight.
  • Photographic infrared ( ColorInfraRed, CIR) is 0.7 to 1.0 microns: Photographic film can absorb this wavelength range.
  • Long-wave part of the NIR range
  • The limitation is due to the water absorption at 1450 nm.
  • Range of thermal radiation at ground temperatures
  • The atmosphere absorbs strongly here, the cosmic 3- Kelvin radiation is on the border of the microwave region just visible.

A frequently used in the Anglo-American subdivision and applied in the specification of Erderkundungskameras is

  • Near infrared ( English: near infrared, NIR) is short -wave IR radiation, which connects directly to the visible ( red ) range from 780 nm to 1400 nm
  • Short-wave infrared (English: short wavelength, SWIR ) 1.4 to 3.0 microns
  • Middle infrared ( English: mid wavelength, MWIR ) with wavelengths of 3.0 microns to 8 microns.
  • Long-wave infrared (English: long -wavelength LWIR ) from 8 to 15 microns
  • Far-infrared (English: far infrared FIR) is long-wave IR radiation from 15 microns to 1 mm and extends into the field of terahertz radiation.


The IR radiation was discovered in 1800 by German - born British astronomer, engineer and musician William Herschel in an attempt to measure the temperature of the different colors of sunlight. He had to fall sunlight through a prism and placed a thermometer in the individual color areas. He noted that it indicated the highest temperature beyond the red end of the visible spectrum. From the observed temperature rise, he concluded that the solar spectrum continues across the Red.


Colloquially infrared radiation is often equated with thermal radiation, even if both microwave and visible light, as the whole electromagnetic spectrum to increase the temperature contribute. Broadband IR sources are thermal emitters such as light bulbs and heaters. Different infrared radiators have been designed in order to cover the wide variety of specific applications of the infrared radiation for example and Globar Nernst pin.


For the detection of IR radiation of all wavelengths thermal detectors ( thermocouples or bolometers ) are suitable. In the short wavelength range semiconductor-based detectors are used ( to internal photoelectric effect ), where digital cameras are suitable if their IR cut filter is not designed to be strong. To record IR images in the near infrared region continues to special photographic films and at longer wavelengths ( near-infrared ) are cooled semiconductor detectors or pyroelectric sensors are used, such as when used in the PIR.



An important application is the heating by radiation. Each radiator also transmits infrared radiation, especially at temperatures significantly above 100 ° C. Below this may outweigh the heat to the air; However, the comfort is increased by the radiation component. Complete home heating or transitional heating in the bathroom are performed by means of infrared panels; the Mir space station was heated in this way since 1986.

Chemical Analysis and Process Engineering

Infrared radiation excites molecules to vibrations and rotations. Infrared spectroscopy is a physical-chemical methods of analysis. The absorption of infrared light of defined wavelengths is used for the structure elucidation of unknown substances. Quantitative determination of the purity of known substances can be determined. One application of infrared spectroscopy for the detection and separation of plastics in waste separation.

The absorption centers of the molecular vibrations are directly related to the refractive index of the material and thus its reflective properties. In the infrared region, this is used, inter alia, in the infrared reflectography.

Art Research

The infrared reflectography is an examination method used mainly in the science of art, with the can on the different reflection properties of the applied on a Malträger colorants make drawing elements from more reflective materials visible. This non-contact and non-destructive technique, it is possible to penetrate the top layer of paint a painting and to document the otherwise invisible signature.


In infrared astronomy observing " cool " objects ( colder than 1000 K ), which are rarely seen in other spectral regions, or objects that are located in or behind an interstellar cloud. In addition, the IR spectroscopy to help in the analysis of the observed objects. Here, certain substances are detected as in chemistry by infrared spectroscopy gangs, such as the methane gas on the exoplanets in stellar HD 189733rd

Electronics and Computer Technology

Infrared remote controls, optocouplers and most photocells operate in the near infrared at 880 to 950 nm wavelength, since silicon photodiodes and phototransistors have their highest sensitivity. Infrared interfaces of computers are also working in this wavelength range and allow for wireless communication with peripherals. Optical data transmission by means of IR laser through the atmosphere is characterized by the free-space optical transmission.

One of the first companies that have infrared technology combined with the computer, Hewlett Packard was. In 1979 they built there the first time an IR port in a calculator, so as to establish a connection to a printer. In 1990, then an IR interface has been integrated into a personal computer for the first time. This interface has become a standard. Since she worked in series, it was Serial Infrared (serial infrared), abbreviated SIR ​​named. For performance reasons, this Standard is now replaced by the backward-compatible fast IR, which supports personal computers from about Year 2002, each desktop motherboard. PDAs and notebooks (up to approximately built 2006), such a infrared device have built, as well as some mobile phones. The infrared interface are increasingly being replaced by Bluetooth.

In the telecommunications IR-A is preferably used due to the low absorption and dispersion in optical fibers. The standard wavelength is 1550 nm

Means of thermal imaging sensors can be motion detection of an infrared radiation source. This is used for example for control of the Wii gaming console from Nintendo.


The near-infrared green vegetation has an approximately six -fold higher than in the visible spectral reflectance as fresh leaf tissue has a good reflectivity, and the other wavelengths are absorbed by chlorophyll and carotenoids accompanying. This effect is used for the detection of vegetation areas. There are two images of a scene taken one in the visible, the other in the near infrared range. Frequently multispectral cameras are used. By dividing both images, the vegetation is clearly visible and can be easily distinguished.

The detected this way vegetation is measured by a vehicle or aircraft. The comparison measurement of vegetation indoor observed a plant over an extended period of time. The measurement of the vegetation from vehicles are a statement about the locally prevailing conditions. The determination of the area fraction of the vegetation to the total surface area of the air captured images is a common case and the vegetation volume within a predefined space is determined. This volume measuring vegetation for highway and road maintenance and rail network operators of importance. Vegetation that protrudes into the loading gauge of vehicles will be detected automatically and the rear section can be initiated.

About the spectral reflectance especially in the near to far infrared by green vegetation vegetation types are distinguished, the respective state of the vegetation is detected. The health of the plant depends primarily on its water supply. The rate of the drought, fungal and insect attack can be seen.


Infrared Photography

In analog photography can be used sensitive special black and white films in the near infrared range up to 820 nm. The visible light is turned off by camera filters, wholly or in large part with red filters. Typical result is the Wood effect: a dark sky imaged and a whitening of the chlorophyll of leaves. This is for example used to penetrate with IR images light haze. This technique is mainly used by the military aerial photography for espionage and military (air and ground ) Enlightenment. On the other hand, color films are used with " false color rendition ." This false-color infrared films are the areas from as visible colors. Are used such materials preferably at aerial photographs, for example for forest damage mapping and in aerial archeology, rare in the artistic field.

Distance measurement

Distance measurement using infrared transit time method - The traveled time of the light emitted from the built-in infrared transmitter light is evaluated in the receiver sensor and automatically transferred to the lens and possibly in the built-in flash. Some versions operate partly in the visible light spectrum and allow the use of optical autofocus systems in low light conditions.


Heating lamps radiate in the infrared and have long been in use for medical purposes.

Thermal radiation of radiant heaters such as ceramic infrared radiators emitting long -wave IR radiation or primarily near infrared red light lamps are used for local treatment of inflammation (such as the sinuses ) are used. For the full body treatment infrared heat cabins are used. Infrared radiation is commonly used in medicine in the form of lasers. The operating environment is particularly the skin, eyes and Dentistry (fairs, sclerosing, cutting, coagulating, light therapy ). Furthermore, it is sought with infrared for the ( warmer ) actual inflammation in order to deal with this effectively. To find local inflammation Thermography is employed.

Near-infrared penetrates deeply into and under the skin, especially during MIR is already absorbed at the surface of the skin and cornea of the eye. Near-infrared high intensity (laser radiation) is therefore particularly dangerous to eyes and skin as it passes unnoticed in the eye to the retina is focused there and can cause damage. On the body, it is absorbed in regions where there are no temperature sensors and can often cause unseen damage.

The temperature measuring pyrometer may be used that measure the temperature in the ear by means of the thermal radiation in the mid infrared. Finally, the pulse oximetry is used to measure the oxygen saturation of red blood cells.

Police and military

Police and military use portable night vision devices and image intensifiers in the near infrared, whose central component is the image intensifier to detect "invisible" objects in the dark can. In addition, infrared light can be used. Helicopter pilots fly at night using a helmet-mounted night vision goggles in the front of each eye a monochrome image of the heat radiation of objects is generated on the ground. The outside of the helicopter, a moving camera can be mounted, which provides in the visible and in the infrared light spectrum video images. These are used for example in the search for missing persons or fugitives in the dark.

Many types of self- homing missile will hit the target by heat radiation, which is emitted for example by aircraft engines. To ward have newer combat aircraft and naval vessels facilities that emit flares (flares ) for diverting these weapons from the target object.


Thermography can be " heat pictures " produce for which the infrared radiation of heat from objects being used. A well-known application is the building thermography for quality control and visualization of thermal bridging and heat loss in buildings. As a result, thermal insulation measures can then be used selectively. The firefighters used portable thermal imaging cameras to detect fire sources and hot spots or persons to be rescued in smoky indoor environments.

In the diagnosis and repair of electrical, electronic and mechanical components, systems or machines, thermography is used as a complementary test method for preventive defects and damage detection. Non-contact can be determined during operation so critical conditions ( "hot spots" ) of machines, equipment and installations to early to take measures to limit the effects and to avoid losses and damages.

Thermography is used in the vibration analysis and strength testing. Cracks and loose connections betrayed by their heat. With Infrarotpyrometern process temperatures and temperatures of components and heat sinks are measured contact and controlled.

Material processing

Many thermal processes in the industry are made by infrared radiation. In addition to use in drying materials cured, are softened and deformed plastics. With infrared lasers materials are welded, labeled and cut metals also hardened. Webs are dried with infrared radiators are electrically heated with gas or. Such additional facilities are available, for example, on paper machines.

Security documents

Infrared sensitive security features in passports and banknotes are checked by infrared lamps. Series can be tested at defined wavelengths in euro bills among other features, the infrared absorption of certain materials. On the other hand, the infrared fluorescence of methylene blue in the British passport is a feature that is used for testing equipment.