infrared

or in·fra-red

[ in-fruh-red ]

See synonyms for infrared on Thesaurus.com

noun

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.

adjective

noting or pertaining to the infrared or its component rays: infrared radiation.

Origin of infrared

First recorded in 1825–35; infra- + red¹

Compare ultraviolet.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use infrared in a sentence

Nor does the jet have the ability to capture high-definition video, utilize an infra-red pointer.
Pentagon Misfires in Stealth Jet Scandal | Dave Majumdar | January 8, 2015 | THE DAILY BEAST
Equipped with both daylight and infra-red cameras, SGR-1 can identify targets at ranges of up to 2.5 miles.
Smoke Rings, Mystery Backpacks and Gun-Toting Robots: The Weird Wartech of the Korean Conflict | Kyle Mizokami | April 3, 2014 | THE DAILY BEAST
The JAS 39E engine is from the U.S., the radar from Britain and the infra-red search and track system is from Italy.
The Planet’s Best Stealth Fighter Isn’t Made in America | Bill Sweetman | March 24, 2014 | THE DAILY BEAST
These are pictures that officers took with infra-red cameras before moving in.
Little Brother | Cory Doctorow
As it began to run a little hot the heat waves streamed out—visible to him as infra-red rays.
The Velvet Glove | Harry Harrison

The bright feral light of the super-mongoose's eyes seemed to lance at Sowles, like an infra-red flash.
Telempathy | Vance Simonds
Infra-red rays are not visible, and we will soon be out of sight of the reflectors.
Astounding Stories of Super-Science July 1930 | Various
In verification of this, I subjected the specimen to the action of infra-red radiation acting from all sides.
Life Movements in Plants, Volume II, 1919 | Sir Jagadis Chunder Bose

British Dictionary definitions for infrared

infrared

/ (ˌɪnfrəˈrɛd) /

noun

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

adjective

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

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for infrared

infrared

[ ĭn′frə-rĕd′ ]

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

a 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.

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