Near-infrared

Where near-infrared sits in the spectrum

Light is classified by its wavelength. The human eye sees about 380 to 780 nm, from violet to red. Beyond red, infrared begins, which the DIN 5031 and CIE standards split into three bands: IR-A (780 to 1,400 nm), IR-B (1,400 to 3,000 nm) and IR-C (from 3,000 nm). Near-infrared is the first of these bands, the one closest to visible light.

The longer the wavelength, the more the radiation is felt as heat. IR-C, far-infrared, is the warmth an infrared cabin or a warm stove gives off. Near-infrared from an LED, by contrast, barely feels warm.

What sets near-infrared apart physically

Skin and tissue absorb light to different degrees depending on the wavelength. Visible light is strongly absorbed by the skin’s pigments (melanin, haemoglobin). Between about 700 and 900 nm this absorption is lower, and water only absorbs strongly at longer wavelengths. Optics calls this range the “optical window” of tissue: near-infrared travels deeper than visible red.

Because the eye cannot see near-infrared, the pupil does not close for bright NIR as it does for visible light. So: do not look straight into an NIR source, and wear the goggles that come with the device.

Band

780–1,400 nm

IR-A under DIN 5031

Typical LED wavelengths

810, 830, 850 nm

Heat

barely felt

with LEDs, unlike incandescent bulbs

Near-infrared at Helsi™

Helsi™ red light panels carry half red LEDs at 660 nm and half near-infrared LEDs at 850 nm. The irradiance of every model is measured and published in the user manual.

The Helsi™ One Sauna Dome pairs far-infrared heaters for the warmth with 132 LEDs: 66 red (630–660 nm) and 66 near-infrared (810, 830 and 850 nm).