infrared

American  

[in-fruh-red] / ˌɪn frəˈrɛd /

Or infra-red

noun

1. the part of the invisible spectrum that is contiguous to the red end of the visible spectrum and that comprises electromagnetic radiation of wavelengths from 800 nanometers to 1 millimeter.

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adjective

1. noting or pertaining to the infrared or its component rays.

   infrared radiation.

infrared British  

/ ˌɪnfrəˈrɛd /

noun

1. the part of the electromagnetic spectrum with a longer wavelength than light but a shorter wavelength than radio waves; radiation with wavelength between 0.8 micrometres and 1 millimetre

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adjective

1. of, relating to, using, or consisting of radiation lying within the infrared

   infrared radiation

infrared Scientific  

/ ĭn′frə-rĕd′ /

1. Relating to the invisible part of the electromagnetic spectrum with wavelengths longer than those of visible red light but shorter than those of microwaves.

2. See more at electromagnetic spectrum

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Closer Look

In 1800 the astronomer Sir William Herschel discovered infrared light while exploring the relationship between heat and light. Herschel used a prism to split a beam of sunlight into a spectrum and then placed a thermometer in each of the bands of light. When he placed the thermometer just outside the red band, where there was no visible color, the temperature rose, as if light were shining on the thermometer. Further experiment showed that this invisible radiation behaved like visible light in many ways; for example, it could be reflected by a mirror. Infrared radiation is simply electromagnetic radiation with a lower frequency than visible light, having longer wavelengths of 0.7 micrometer to 1 millimeter. Ultraviolet radiation, like infrared radiation, lies just outside the visible part of the spectrum, but with higher frequencies; some animals, such as bees, are capable of seeing such radiation. Both infrared and ultraviolet radiation are often referred to as forms of light, though they cannot be seen by human beings. Heat energy is often transferred in the form of infrared radiation, which is given off from an object as a result of molecular collisions within it. Molecules typically have a characteristic infrared absorption spectrum, and infrared spectroscopy is a common technique for identifying the molecular structure of substances. Astronomers similarly analyze the infrared radiation emitted by celestial bodies to determine their temperature and composition.

Etymology

Origin of infrared

First recorded in 1825–35; infra- + red ¹

Compare meaning

How does infrared compare to similar and commonly confused words? Explore the most common comparisons:

• infrared vs. ultraviolet

Example Sentences

This allowed the researchers to analyze its structure with high precision using infrared spectroscopy.

From Science Daily • Apr. 7, 2026

In this process, three infrared photons combine into one photon with a higher frequency, effectively converting infrared light into visible blue light.

From Science Daily • Apr. 5, 2026

Embarking on expeditions in vast and sometimes dangerous environments, Bigfoot hunters set out with drones, infrared cameras, audio recorders and materials to cast footprints.

From BBC • Apr. 3, 2026

This ranges from shapes captured on trails or infrared cameras to a howl or witness testimony, allowing Bigfooters to hypothesise what that means about the beast's "anatomy, behaviour, sociality and levels of intelligence".

From BBC • Apr. 3, 2026

Kyle stayed on his direct trajectory to Flora and Ulysses, but within seconds, his hover ladder’s infrared collision sensors picked up the approach of Marjory’s platform.

From "Mr. Lemoncello's Library Olympics" by Chris Grabenstein

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