FAR-INFRARED RADIANT SAUNAS
The Electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, microwave, and radio waves. The only difference between these different types of rays is their wavelength frequency. Wavelength increases and frequency (plus energy and temperature) decreases from gamma rays down to radio waves. All these forms of rays travel at the speed of light. Infrared lies between the visible and the microwave portions of the electromagnetic spectrum. The infrared waves have wavelengths longer than visible and shorter than microwaves and have frequencies which are lower than visible and higher than microwaves. Near infrared refers to the point of the infrared spectrum that is closest to visible light and far infrared (long wavelengths) refers to the part that is closer to microwave regions of the spectrum.
When an object is not quite hot enough to radiate visible light, it will emit most of its energy in the infrared, ie.: hot charcoal may not give off light, but does emit infrared rays which we feel as heat. We experience infrared everyday. The heat that we feel from sunlight, a fire, a radiator is infrared. Although our eyes cannot see it, the nerves in our skin can feel it as heat.