What wavelength is red light?

Visible red is about 620 to 780 nm. Red light devices mostly use 630 to 660 nm; Helsi™ red light panels use 660 nm.

What wavelength is infrared?

Infrared starts at 780 nm. Near-infrared (IR-A) runs to 1,400 nm, IR-B to 3,000 nm, and far-infrared (IR-C) lies above that.

What wavelength is heat radiation?

Heat travels mainly as long-wave infrared (IR-B and IR-C, from 1,400 nm). A warm body or an infrared cabin radiates mostly in the far-infrared.

What is the difference between 660 nm and 850 nm?

660 nm is visible red; 850 nm is invisible near-infrared. Tissue absorbs 850 nm less strongly, so it travels deeper.

Do LED red light panels emit UV?

No. Red and near-infrared LEDs emit only in their narrow band around 660 and 850 nm, far from the UV range below 380 nm.

Glossary

Wavelength (nm)

Wavelength is the distance between two crests of a light wave; for light it is given in nanometres (nm, millionths of a millimetre) and sets its colour, or its place in the spectrum.

Also: nm, nanometre, red light wavelength, infrared wavelength

Updated November 1, 2026

Wavelengths at a glance

Short wavelengths carry more energy per photon, long ones less. Below 380 nm is ultraviolet, from 380 to 780 nm visible light, above that infrared. Red light and infrared devices differ mainly in which of these ranges they emit and how narrow or broad their spectrum is.

Range	Wavelength	Example
UV-B / UV-A	280–380 nm	Sun, tanning bed
Visible light	380–780 nm	Red from about 620 nm
Red in red light devices	630–660 nm	Helsi™ red light panels: 660 nm
Near-infrared (IR-A)	780–1,400 nm	Helsi™ red light panels: 850 nm
IR-B	1,400–3,000 nm	Part of an incandescent bulb’s output
Far-infrared (IR-C)	from 3,000 nm	Heaters of an infrared cabin

Narrow or broad: LED versus bulb

An LED emits a narrow band around one wavelength, typically about 20 to 30 nm wide. That is why a maker can say a panel emits “660 nm”.

A classic heat lamp, an incandescent bulb behind red glass, emits a broad spectrum, most of it infrared that arrives as heat. The red glass filters visible light down to its red share.

LED bandwidth: about 20–30 nm
Helsi™ red: 660 nm
Helsi™ NIR: 850 nm

What to check in a spec sheet

Actual values: reputable makers state wavelengths in nm, not just “red light” or “infrared”.
Shares: the spec sheet says how many LEDs have which wavelength. At Helsi™ it is half and half.
Irradiance: wavelength says nothing about power per area. That is given as mW/cm² at a stated distance.

More at Helsi™

See the Helsi™ red light panels Red light therapy guide

Frequently asked questions

More questions? Our team in Germany can help.

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All terms in the glossary