Wavelength (nm)

The plain version. Light travels as a wave. Wavelength is the length of one cycle of that wave, and it is what your eye reads as colour. Short wavelengths look blue or violet; long ones look red; beyond red, light becomes invisible infrared, felt as warmth rather than seen.

The conventional bands. Using the internationally standard divisions: ultraviolet A runs 315–400 nm; visible light runs roughly 400–780 nm, with blue near 450–490 nm, green 500–570 nm and red 620–780 nm; IR-A, commonly called near infrared, runs 780–1400 nm; IR-B runs 1400–3000 nm; and IR-C, which the sauna industry calls far infrared, runs from 3000 nm to 1 mm.

Why it matters so much. Absorption is wavelength-specific. Haemoglobin, melanin, water and cytochrome c oxidase each absorb strongly at some wavelengths and weakly at others, which is why a 12,000 nm emitter warms the skin surface while an 850 nm emitter passes further in. Change the wavelength and you change what is absorbed, how deep the light reaches, and which research is relevant.

How to read a specification. “630 nm” describes a peak. Real LEDs emit a band around that peak, typically tens of nanometres wide. A stated range describes the span across several different emitters rather than a single continuous output, and tells you nothing about intensity.

Our own range. The Red Light range runs from 460 nm to 12,000 nm — visible blue at the short end, through green and red, to near infrared at 850 nm and far infrared at 12,000 nm. There is no ultraviolet emission.