infra-red

 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.]

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

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