660nm vs. 850nm: What Do the Numbers on a Light Therapy Device Actually Mean?

If you've shopped for a red light therapy device for your dog, you've probably seen these numbers everywhere: 660nm, 850nm, sometimes a range like 830-880nm. Most listings throw them around without explaining what they actually mean — which makes it hard to tell a genuinely well-specified product from one that's just copying language from a competitor.

Here's what those numbers actually represent, and why the combination matters more than either number alone.

"nm" Just Means Nanometers — It's Measuring Color

"nm" stands for nanometer, a unit of measurement for the wavelength of light. Every color of visible light has its own wavelength — what we perceive as different colors is our eyes reading different wavelengths. Red light sits at the longer-wavelength end of what we can see; near-infrared sits just past it, technically invisible to the human eye.

So when a product says "660nm," it's telling you exactly what shade of red light it produces — not a vague "red light," but a specific, measurable point on the light spectrum.

660nm: Visible Red Light, Works at the Surface

660nm is visible red light. It's absorbed primarily by the upper layers of skin and muscle tissue — it doesn't penetrate especially deep, but it works efficiently right where it lands. This is the wavelength most associated with supporting skin and coat health and surface-level comfort.

850nm: Near-Infrared, Invisible, Works Deeper

850nm sits just beyond the visible spectrum, in the near-infrared range — your eyes can't actually see this light doing anything, even though it's there and active. Because of its longer wavelength, near-infrared light penetrates further into tissue, reaching muscle, connective tissue, and joints in a way that 660nm alone doesn't reach as effectively.

Why the Combination Is What Actually Matters

Here's the part most marketing skips: neither wavelength alone gives you full coverage. 660nm works at the surface. 850nm works deeper. A device using only one or the other is only doing half the job for something like joint support, which benefits from light reaching below the surface, not just the skin.

This is why the research specifically supporting light therapy for joint conditions in dogs uses a combined approach — the controlled trials showing measurable benefit for canine osteoarthritis used devices delivering both wavelengths together, not a single-wavelength device.^1,2

What to Actually Check Before Buying

A few practical things worth verifying on any device, ours included, before you buy:

• Does it list both wavelengths specifically, or just say "red light" vaguely? Vague language is often a sign the manufacturer doesn't know or isn't disclosing the actual specs.
• Is the near-infrared wavelength in the range used in the research (roughly 800-880nm)? Some cheaper devices use a single wavelength stretched to try to do both jobs, which isn't the same thing.
• Does the listing disclose diode count or power output, not just wavelength? Two devices can use the same wavelengths and still perform very differently depending on how many LEDs are actually doing the work.

WoviePet products use 660nm red + 850nm near-infrared specifically because that's the combination the research actually points to — not because it's the version that sounds most impressive on a label.

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WoviePet products are intended to support comfort, circulation, and mobility, and are not intended to diagnose, treat, cure, or prevent any disease. Always consult your veterinarian about your dog's specific health needs.

Sources

1. Randomized, double-blind controlled trial — photobiomodulation for canine hip osteoarthritis. https://pubmed.ncbi.nlm.nih.gov/35895799/
2. Randomized, placebo-controlled trial — photobiomodulation for canine elbow osteoarthritis. https://pubmed.ncbi.nlm.nih.gov/30197438/