Infrared is part of the light spectrum that shines down from the sun and supports life on earth. Sunshine consists of Ultra-Violet (UV), Visible Light and Infrared light. All light when it hits an object is either reflected off the object, absorbed by the object or transmitted through the object.
An infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the infrared radiation ranges from 780 nm to 1 mm. The relationship between temperature and wavelength is expressed by Wien's displacement law. No contact or medium between the two bodies is needed for the energy transfer.
In the case of an Infrared sauna, the object is your body that is being hit by the Infrared light and to generate heat in your body the Infrared must be well absorbed. Absorption of the radiant energy is required to generate heat.
