"Doesn't Infrared Go Deeper? So Isn't It Just Better?" - Science of Light

It's one of the most common questions we get, and it's a genuinely smart one. If near-infrared light penetrates deeper into the body than red light, then isn't near-infrared simply the better wavelength? Why would anyone bother with red light at all?

It's such a reasonable question that the entire industry has more or less agreed on a tidy answer: red light for the surface, near-infrared for the deep stuff, and "penetration depth" as the number that separates the two. You'll see charts everywhere — red reaches a few millimetres, infrared reaches a few centimetres, therefore infrared wins for anything below the skin.

Here's the thing. That answer isn't exactly wrong, but it's so simplified that it becomes misleading. It treats light like a nail gun, where the only question is how far the projectile travels. But light doesn't behave like a projectile in tissue at all. And once you understand how it actually behaves — how it's absorbed, how it scatters, and what your body does with it — the relationship between red and near-infrared light stops looking like a competition and starts looking like a genuine partnership. That partnership is one of the most beautiful things about this whole therapy, and almost nobody explains it.

So let's actually explain it.

"Penetration depth" is a magic trick that hides the real story

Start with the phrase itself, because it's doing something sneaky. "Penetration depth" makes you picture a photon flying in a straight line, punching through layers of tissue, and stopping at a certain depth like a bullet running out of momentum. Deeper equals more powerful, in that picture. Deeper equals better.

But that's not what happens. When light enters tissue, two completely different things are happening to it at once, and only one of them is "depth."

The first is absorption — a photon hits a molecule that can catch it, hands over its energy, and ceases to exist as light. That's not a loss. That's the entire point. Absorption is where the therapy happens. A photon that is never absorbed does nothing at all.

The second is scattering — a photon bounces off the boundaries between structures with different densities and changes direction, over and over, ricocheting through the tissue like a pinball. And here's the fact that breaks the whole "deeper is better" model: in the wavelengths we use for therapy, scattering is overwhelmingly the dominant event. In muscle tissue, for a red wavelength around 670 nanometres, the scattering effect can be on the order of two hundred times stronger than absorption. Light in your body is not a bullet. It's a fog rolling through a forest, bending around every trunk.

So when a chart tells you red light "only reaches three millimetres," what's really happening is that red light is scattering intensely and being absorbed quickly in the tissue near the surface. It's not that the photons are weak. It's that they're getting caught — which, again, is the goal. And near-infrared reaches "deeper" not because it's more powerful, but because it happens to be absorbed and scattered less on the way in, so more of it survives to travel further before it finally interacts.

Read that again, because it flips the whole intuition. Red light isn't the weak one that can't get deep. Red light is the one that gets used up faster — because the surface is exactly where it's designed to work. And near-infrared doesn't win by being stronger. It wins the depth contest specifically by interacting less on its journey. Depth and effect are almost in tension, not alignment.

There's even a lovely wrinkle here that shows how counterintuitive this all is: because near-infrared scatters so much once it's inside, all that ricocheting actually increases the total distance each photon travels, which increases the odds it eventually gets absorbed somewhere in the depths. The scattering that seems like it should be a problem is part of how the deep tissue gets its dose.

The sun already taught us this — and we ignored it

Here's a question that reframes everything. Why do we consider sunlight so profoundly valuable for life?

It is not because sunlight penetrates deeply. Most of the visible sunlight that does anything meaningful for you is absorbed at or very near the surface — in your skin, in your eyes. The value of sunlight has never been about how far it burrows into you. It's about what gets absorbed, and what that absorption sets in motion.

Think of a plant. A leaf is, at most, a fraction of a millimetre of working tissue. Sunlight doesn't need to "penetrate deep" into a forest floor to power the entire forest — it's absorbed in that thin green layer, and from there the energy is captured, converted, and distributed through the whole organism. Photosynthesis is a surface event with whole-body consequences.

We've somehow imported a "deeper is better" mindset into light therapy that we would never apply to the benefit of sunlight. Nobody says sunlight doesn't have health effects because it doesn't reach your femur. We understand, instinctively, that the sun's power lies in absorption at the surface and everything that cascades from it. Red light deserves exactly the same respect. Being absorbed near the surface isn't a limitation. For the surface, it's the whole design — and as we'll see, the surface may be doing far more for the rest of the body than "surface" implies.

Your skin: a biological solar panel

Here's a framing we love, because it reorganizes how you think about the whole thing. Your skin is not just a barrier. It behaves, in a real sense, like a biological solar panel.

A solar panel doesn't need light to pass through it to be useful. Quite the opposite — its entire job is to absorb light at its surface and convert that energy into something the rest of the system can use. It's valuable precisely because it catches photons, not because it lets them through.

Your skin, richly supplied with blood vessels, packed with mitochondria-dense cells, and wired into your nervous, immune, and circulatory systems, does something remarkably analogous. When red light is absorbed in that superficial layer, it's not a dead end. It's an intake. The energy caught there drives cellular processes, shifts the local chemistry, changes what the blood flowing through that region carries away with it, and sends signals outward. The photons stop at the surface. Their consequences do not.

Which sets up the single most important idea in this entire article: the difference between a local effect and a systemic one.

Local versus systemic: why "where the light lands" isn't "where the benefit lands"

Here is the assumption buried inside the "deeper is better" question: that the light has to physically reach a tissue in order to help it. That to benefit a deep structure, a photon must arrive at that structure. That assumption is increasingly looking incomplete.

There's a growing and genuinely fascinating body of research into what are sometimes called the systemic, remote, or abscopal effects of light therapy — the finding that shining light on one part of the body can produce measurable effects in distant parts the light never reached. In one striking recent line of human research, near-infrared light delivered to the torso improved a measure of vision roughly a day later — even when the eyes themselves were completely shielded from the light. The benefit reached the eye through the body, not through the pupil.

How? The leading explanation is that light doesn't only act where it lands — it changes the signals that then travel everywhere. When light is absorbed at the surface, it alters the mix of signalling molecules in the blood and tissue: cytokines and other messengers that then circulate throughout the body carrying the instruction onward. The photon's journey ends at the surface. The message's journey is just beginning.

This is why "the light only reaches three millimetres" can be a red herring. If a surface interaction shifts your whole-body inflammatory signalling, or changes what your circulating immune cells are doing, then the depth the photon physically reached tells you very little about the depth of the benefit. A surface event with systemic consequences — exactly like the sun, exactly like a solar panel.

None of this means depth is entirely irrelevant. For a local problem in a structure under many layers — an arthritic hip joint, a tendon buried under a horse's cannon bone — you genuinely do want near-infrared, because you want meaningful energy delivered at that spot to drive local repair. Local effects are real and they matter enormously; it's a large part of why we build with near-infrared at all. The point is simply that local delivery is one of the two things light does, not the only thing. And red light, working powerfully at the surface, is a full participant in the other.

The Science of Light : a few ideas worth knowing

Now we step into more speculative territory, and we're going to be honest about that, because this is where the marketing in our industry tends to abandon all discipline. The following ideas are genuinely being researched, they're mechanistically interesting, and they are not settled science. We share them because they're fascinating and because they each add another reason the red-versus-infrared "which is better" framing falls apart — not because we'd ever build a promise on them.

Melanin, and why red light isn't "just" surface-level. Melanin is best known as the pigment that colours skin, but it's a genuinely remarkable molecule that absorbs across an enormous span of the electromagnetic spectrum. Established science already tells us that melanin's absorption is one of the things shaping how light of different wavelengths behaves in skin — and notably, red and shorter wavelengths interact with melanin far more than near-infrared does. That alone is a clue that red light is doing specific work at the surface that infrared largely skips past. Beyond that, there's an emerging and more speculative body of work proposing that melanin acts as a kind of internal energy hub — capturing photon energy, including from the very wavelengths red light delivers best, and redistributing it locally to support other processes. If that pans out, it would be yet another job happening at the surface, in red light's territory, that "infrared goes deeper so it's better" completely misses. Interesting? Very. Proven? No. File it under "watch this space" — but notice which wavelength it points back toward.

Biophotons — and why depth may be the wrong lens entirely. This one surprises people. Your cells emit an ultra-weak stream of light of their own, constantly — a genuine, measured phenomenon called ultraweak photon emission, or biophotons, on the order of a handful to a few hundred photons per second. It arises mostly from the ordinary chemistry of your mitochondria and from reactive oxygen species. That much is established. What it means — whether these biophotons are just a metabolic byproduct or an actual signalling system the body uses, and whether external light meaningfully interacts with that system — is very much an open research question, and a debated one. But here's why it belongs in this conversation: if any part of light's benefit runs through a signalling system like this rather than through a photon physically arriving at a target, then "how deep does this wavelength reach" stops being the right question altogether. A red photon absorbed at the surface could, in principle, matter just as much as an infrared photon delivered deep. We're not claiming it does — we're pointing out that the deeper-is-better logic quietly assumes depth is what counts, and this is one of several reasons that assumption may be too simple. Be most skeptical of anyone claiming certainty here.

Light, heat, and where each wavelength does its work. All chemical reactions in your body — every repair, every synthesis — depend on molecules having enough energy to react. There's a real and established mechanism worth understanding, and it actually helps explain the division of labour between the two wavelengths. As you move toward and past the near-infrared, light energy absorbed by water in tissue produces gentle, local thermal effects, and that mild warming genuinely can influence local chemistry — this is well documented, and it's part of what near-infrared contributes in the deeper tissue it reaches. Red light, absorbed more by pigments and less by water, works through a somewhat different balance of effects nearer the surface. So even the "heat" story isn't an argument for one wavelength over the other — it's another example of the two doing different jobs in different places. Where it does get speculative is the more expansive claims about "photon build-up" and body-wide energetic effects; the honest version is that light deposits energy, some of that energy is thermal, warmth affects reaction rates, and that's real, modest, and not the same as the grander stories sometimes told about it.

We include these not as selling points but as a window into how genuinely deep and unfinished this science is — and notice the pattern running through all three. Every one of them, when you follow it, points back toward the same conclusion: that framing red and near-infrared as rivals, with depth as the scoreboard, misses most of what's actually happening. The honest state of knowledge is that red and near-infrared light do powerful, well-documented things at different depths and through different mechanisms, and around the edges of that solid core sit a set of beautiful, half-understood ideas — several of which suggest the surface work red light does may matter more, not less, than the depth charts imply. A company worth trusting can tell you which is which.

So why not just use near-infrared for everything?

Let's come all the way back to the original question, because now we can answer it properly.

Red light and near-infrared light are not competitors, and they are not two separate tools assigned to two separate zones of the body. They are two overlapping ways of interacting with the same living tissue, absorbed by overlapping-but-different targets, and the reason they work so beautifully together is that the body itself refuses to be sorted neatly into "surface" and "deep."

Consider what tissues are actually made of. Your skin isn't only an outer wrapper — it's dense with collagen, packed with blood vessels, and those vessels are themselves lined with muscle. A muscle deep in your thigh isn't a different substance from your skin — it's fed by blood, built on connective tissue, threaded with the same collagen and the same repair machinery. A tendon is largely collagen, the very protein red light is so good at influencing, yet it may sit centimetres down. An artery is muscle and connective tissue, and it runs both just beneath your skin and deep through your core. The categories "surface tissue" and "deep tissue" are a convenience, not a biological fact. The same building blocks — collagen, blood, muscle fibre, mitochondria — appear at every depth.

Which is exactly why you want both wavelengths, and why they reinforce rather than divide the labour. Red light around 660 nanometres is absorbed strongly and works powerfully in the outer layers — but "the outer layers" already includes collagen, superficial blood vessels, and the smooth muscle in their walls, and its effect on that richly-vascularized surface feeds into whole-body signalling that reaches far beyond where the photons stopped. Near-infrared around 850 nanometres survives the journey to deliver energy directly to a deep muscle belly or a buried tendon — but those deep structures are made of the same collagen and carry the same blood that red light acts on nearer the surface, so the two wavelengths are often working the same biological processes, just entering them at different points.

Picture treating a tendon injury. The near-infrared reaches down to the tendon body itself to support repair at depth. The red light works powerfully on the skin and superficial tissue above it — and on the small vessels there that carry blood, oxygen, and signalling molecules down toward the healing site. Collagen is being supported at the surface and at depth. Circulation is being encouraged from the skin inward and at the tendon itself. Inflammation is being modulated locally and, potentially, systemically through the bloodstream. It isn't "red for the skin, infrared for the tendon." It's two wavelengths converging on a single, connected, three-dimensional healing process from different angles. Red light is largely used up near the surface because that's where a huge amount of the vascular and collagen work begins. Near-infrared travels further because it interacts less along the way, saving its energy for the deep spot. Neither fact makes one superior. Together they cover a job that neither could do alone.

This is exactly why serious devices, including ours, deliver both. Not as a marketing checkbox, but because the two wavelengths overlap across the whole depth of the tissue, meeting the same collagen, the same blood vessels, the same repair processes from different distances. Using only near-infrared because "it goes deeper" would mean under-serving the intense surface work — the vascular and collagen and signalling work — that red light does best, some of which sends benefits inward and body-wide. Using only red would mean surrendering the direct deep-tissue delivery near-infrared does so well. The wavelengths aren't dividing the body between them. They're double-covering it.

The beauty of this therapy was never that one magic wavelength drills deepest. The beauty is that light interacts with living tissue in layered, overlapping, still-partly-mysterious ways — and that two well-chosen wavelengths, working together, meet the body across the full range of how it actually uses light.

Deeper isn't better. Together is better. And that's a far more interesting answer than the charts would have you believe.

Want to understand the science behind light therapy — properly, honestly, and without the hype? Explore EquiGlow Therapeutics' dual-wavelength red and near-infrared devices at equiglowtherapeutics.ca, and dig deeper on our podcast, GlowUp Sessions, where we take apart questions exactly like this one. Learn first. Glow up second.

EquiGlow Therapeutics is a Canadian photobiomodulation company specializing in red and near-infrared light therapy devices for humans, horses, and dogs. This article is for educational purposes only and is not medical or veterinary advice. Emerging and speculative concepts are identified as such; always consult a qualified professional for health concerns.