Heat, infrared and the body's response
Near-infrared (NIR)
Near-infrared (NIR) is the band of infrared light closest to visible red, roughly 780 to 1,400 nanometres. It passes several millimetres into tissue rather than being absorbed at the surface, which is why it is used as a light modality rather than as a heat source.
Also called NIR, IR-A, 850 nm light
Infrared is light with wavelengths longer than the eye can see. Near-infrared (NIR) is the short-wavelength end of it, the part nearest visible red. The photobiological convention of the International Commission on Illumination (CIE) puts IR-A at 780 to 1,400 nanometres (nm). ISO 20473, a different scheme, instead defines near infrared as 0.78 to 3 micrometres.
Why it behaves differently from far infrared. Between roughly 650 and 1,200 nm, water and haemoglobin both absorb comparatively weakly — the optical window — so light in this band travels millimetres into tissue before it is absorbed. Far infrared, at 3,000 nm and above, is absorbed by water almost immediately at the skin surface. NIR and FIR are not two strengths of the same thing: NIR is a light modality, FIR a heating one. They share a glossary group only because both are called infrared.
What is fitted. The Red Light Ozone Steam Sauna carries 380+ near-infrared LEDs at 850 nm, arranged as full-body-length strips inside the sauna. On eye exposure the answer is design rather than eyewear: the user’s head is outside the sauna, away from the direct line of the emitters, and the lights in the doors switch off when a door is opened.
Where the research is. Our near-infrared studies page collects the literature and links on to its sources.
Why it matters here
If you are comparing the Red Light model against a red light panel, 850 nm is the specification that matters most. It is a different feature from the far infrared heating on the Standard and Deluxe, even though both are called infrared.