far-infrared radiation

noun

1. the longer wavelengths of electromagnetic radiation in the infrared region of the spectrum, beyond the red end of the visible spectrum, from 50 to 1000 micrometers. Abbreviation: FIR

1. Infrared electromagnetic radiation of very long wavelengths, in the range of 2-50 microns. It is used in medicine to provide a penetrating heat to the body. Also called far-red radiation