Light and photobiomodulation
Nanometre (nm)
A nanometre (nm) is one billionth of a metre — a thousandth of a micrometre, or a millionth of a millimetre. It is the standard unit for light wavelengths. A micron, used for far infrared specifications, is a micrometre: 12 microns is 12,000 nm.
Also called nanometer, nm
The unit. The nanometre is an SI submultiple of the metre: 1 nm = 10⁻⁹ m. For scale, a human hair is roughly 80,000 nm across, and a red blood cell about 7,000 nm.
Why light is measured in it. Visible light wavelengths land conveniently in the hundreds of nanometres, so a colour can be quoted as a single tidy number. Blue is roughly 450–490 nm, green 500–570 nm, red 620–780 nm.
The micron trap. Infrared emitters are often specified in microns (µm) rather than nanometres, and the two get mixed in the same sentence. One micron is 1,000 nm. Our Standard and Deluxe saunas are specified around 12 micron far infrared, which is 12,000 nm, and that is the same figure quoted as the top of the Red Light sauna’s range. If you see 12 and 12,000 in different documents for the same product, they agree — the units differ.
A practical reading tip. Numbers in the hundreds are almost always visible light or near infrared in nanometres. Numbers in the thousands are either far infrared in nanometres or, if they carry a µm sign, something very much longer. Check the unit before comparing two devices, because a factor of a thousand is the difference between light you can see and radiant heat you can only feel.
Why it matters here
Infrared is quoted in microns on some datasheets and in nanometres on others. Knowing that 12 microns and 12,000 nm are the same figure stops two products looking different when they are in fact the same.