infrared

Of or relating to electromagnetic radiation between microwaves and red visible light in the electromagnetic spectrum, having frequencies between 300 gigahertz and 400 terahertz and wavelengths between 1 millimeter and 750 nanometers.

Generating, using, or sensitive to infrared radiation.

Infrared light or the infrared part of the spectrum.

Below the 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.