Sunlight is a combination of visible and invisible light. Infrared and ultraviolet rays are part of the invisible spectrum of light.
Infrared rays are the healthiest and safest rays produced by the sun; penetrating deeply into the skin dissolving harmful substances accumulated in your body. The far infrared rays consist of similar wavelength as that which is emitted naturally by the human body.
The infrared saunas use infrared rays to heat your body directly without warming the air around you.