a. [ Infra- + red. ] 1. (Physics) Lying outside the visible spectrum at its red end; -- said of rays having a longer wavelength (and thus less refrangible) than the extreme red rays, specifically those electromagnetic waves having a wavelength of between 700 nanometers and 1 millimeter. [ Webster 1913 Suppl. +PJC ]

2. relating to, using, or producing infrared radiation. [ PJC ]

3. affected by infrared radiation; as, infrared detector; infrared film. [ PJC ]

n. [ Infra- + red. ] (Physics) electromagnetic radiation having a wavelength of between 700 nanometers and 1 millimeter. Infrared radiation is that electromagnetic radiation lying between the visible spectrum and the longest microwaves. It may be absorbed by matter in a manner specific to the absorbing substance, causing increased vibration of molecules. The infrared absorption spectrum of a chemical compound is often very specific, and the infrared absorption spectrum is therefore used to help identify chemical substances. Infrared radiation is used in certain communication devices, such as television remote controls and communication devices between computers or between computers and peripherals. [ PJC ]