Full spectrum infrared energy is the healthiest part of the solar electromagnetic spectrum, the Sun. The infrared frequencies are invisible to the naked eye, but are felt within the body as deep penetrating heat and warmth felt when you are in the sun. Full Spectrum Infrared energy includes the three wavelengths in the infrared spectrum... near (NIR), mid (MIR), and far (FIR) frequencies. NASA scientists have determined their differing wavelengths and health science studies have determined what these different wavelengths do, which is one of the reasons Therasage devices generate the Full Infrared Spectrum, to deliver all these health benefits essential for natural healing To the body, in one sauna!!