Is Your Red Light Therapy Actually Working?
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If you are getting your red light therapy (rødlysterapi) sessions in wearing a t-shirt, or standing a metre and a half back because you read somewhere that "full body coverage" is the goal, then I have some news that you probably need to hear. What you are doing may not be photobiomodulation at all. It may be something else entirely. Not nothing, necessarily, but not what you think it is, and not what the research you've been reading was testing.
This is not a small distinction. It is actually the whole game.
What Photobiomodulation Actually Is
Let me start at the level where it actually matters, which is quantum physics, because that is where photobiomodulation (fotobiomodulasjon) lives.
PBM is not warmth. It is not colour perception. It is not a vague wellness sensation. It is a photochemical and photophysical process that depends entirely on a specific event happening: a photon of the correct wavelength being absorbed by a specific light-sensitive molecule inside your cells. This is governed by something called the Grotthuss-Draper Law, which states that only light that is actually absorbed can produce a photochemical effect. Light that bounces off, scatters into nothing, or gets absorbed by something else entirely... does nothing to your mitochondria.
The primary target molecule in PBM is cytochrome c oxidase, or CCO. It is the terminal enzyme in the mitochondrial electron transport chain, the molecular machine that drives ATP production in almost every cell of your body. Dr. Michael Hamblin at Harvard has published extensively on this. Prof. Glen Jeffery at University College London. Dr. Alexander Wunsch in Germany. These are not fringe figures. They are serious researchers describing a mechanism that is now reasonably well established in the photobiology literature.
CCO has absorption peaks in the red range around 630 to 680nm, and in the near-infrared range around 800 to 880nm. When a photon at one of those wavelengths reaches a CCO molecule, it excites an electron from its ground state to an excited state. This is a discrete quantum event. It either happens or it does not. There is no partial version. And when it does happen, the cascade of effects that follow includes the release of nitric oxide, enhancement of the proton gradient, increased ATP synthesis, and downstream anti-inflammatory and regenerative signalling.
That is what you are trying to produce. Not a colour therapy experience. Not a mood effect from a warm glowing light. A specific intracellular photochemical event, billions of times over, in tissue that is several millimetres beneath your skin surface.
Now think about what stands between your panel and those mitochondria when you are wearing a t-shirt.
The Clothing Problem
Even a light-coloured cotton t-shirt absorbs and scatters a substantial portion of red and near-infrared photons before they ever reach your skin. A darker garment absorbs even more. The fibres act as a matrix of scatterers and absorbers. Photons that do pass through are randomised in direction, reduced in intensity, and arrive at the skin surface with a fraction of their original irradiance.
Here is why this matters at the biology level. The dose in PBM is calculated as fluence: irradiance in mW/cm² multiplied by time in seconds, giving you a result in joules per square centimetre. The research literature suggests minimum effective fluence thresholds for meaningful cellular response sit around 1 to 4 J/cm², depending on the tissue and the target depth.
Here is the catch that most people don't appreciate. Even with perfect bare skin and optimal distance, tissue optics alone mean that only around 5 to 10% of incident photons at 630nm reach a depth of 5 to 8mm. Scattering by melanin, haemoglobin, collagen and water accounts for the rest. So you are already starting with a significant attenuation before you even get to the mitochondria in deeper tissues.
Add fabric on top of that, and the photon flux arriving at mitochondrial depth is almost certainly below the threshold required to drive a measurable biochemical cascade. You have not reduced your session effectiveness by 20%. You have potentially eliminated the primary mechanism altogether.
What you may still be experiencing is something real but different. Warmth from the infrared component. A mild mood or alertness effect from retinal photoreception. Something resembling colour therapy or chromotherapy, a psychophysiological response mediated by the nervous system rather than intracellular photochemistry. These are not nothing. But they are not what Dr. Hamblin's lab was studying. They are not what the clinical trials on wound healing, muscle recovery, and joint pain were testing. And they are not what you think you are buying when you invest in a proper PBM panel.
Bare skin is not a preference. It is the mechanism.
The Distance Problem Is More Complicated Than You Think
Now the distance question, and I want to be precise here because this is where people get the physics genuinely wrong, including some people who should know better.
You may have heard of the inverse square law: double the distance, irradiance drops to one quarter. This is real physics. But here is what most explanations miss. The inverse square law applies to point sources. A single bulb. A star. Something that radiates in all directions from a single location.
A 300 LED panel is not a point source. It is an extended planar source. And this changes everything about how the irradiance behaves with distance.
When you are standing close to a large LED panel, you are receiving photons from a very wide spread of emitters simultaneously. Every LED in your field of view is contributing to the irradiance at your skin. As you move back slightly, yes, each individual LED contributes a bit less. But the inverse square law's dramatic drop-off is substantially buffered by the fact that you are still receiving photons from the entire panel.
The result is that for a large LED panel in what physicists call the near field, meaning distances that are small relative to the panel's physical dimensions, irradiance drops off much more gently than the inverse square law would predict. Closer to a 1/r relationship in the near field, rather than the 1/r² of the inverse square law. The exact behaviour depends on the panel size and geometry, but the principle holds across all extended planar sources.
Here is the practical implication. Many people see the inverse square law quoted in PBM contexts and apply it directly to panels. They conclude that moving from 15cm to 30cm halves their dose, so they compensate by doubling session time. This is not how it works for large panels. The irradiance drop at that range is more modest than pure inverse square maths would suggest.
However, and this is the part that actually matters for the clothing and distance question: the near-field protection has limits. Once your distance from the panel becomes large relative to the panel's dimensions, the physics starts converging toward point-source behaviour, and the inverse square law starts to dominate.
For a typical consumer PBM panel, say 30 by 60cm to 60 by 90cm, this transition begins somewhere around 50 to 100cm, and by 1.5m you are well into the territory where the irradiance has dropped significantly. At most consumer panels, 1.5m puts you at an irradiance that is comparable to sitting near a window in reasonable daylight. Genuinely, that is roughly the photon flux level you are at. Your mitochondria cannot distinguish this from ordinary indoor light exposure. The specific PBM signalling cascade is not being triggered.
So What Is Happening at 1.5 Metres?
Something real, just not PBM. The retinal photoreceptors, particularly the intrinsically photosensitive retinal ganglion cells (ipRGCs) that drive circadian biology, respond to light levels well below the PBM threshold. You may get a genuine circadian signal. Serotonin synthesis may be mildly upregulated. There may be a warmth and wellbeing effect from the infrared component.
This is the territory of light therapy lamps, SAD devices (vinterdepresjon-lamper), and general phototherapy. Real, useful, and with a good body of evidence behind it. But the mechanism is neuroendocrine and retinal, not mitochondrial. The distinction matters enormously if you are trying to address specific physical issues: joint pain (leddsmerter), muscle recovery (muskelgjenoppretting), wound healing, or deep tissue work.
For those applications, you need photons to reach tissue at depth. Tissue that cannot be reached at 1.5m through the skin optics budget, regardless of what the inverse square law does or doesn't do to the irradiance en route.
For Us in Norway: This Matters More in Winter
ESPECIALLY IMPORTANT HERE IN NORWAY. We are light deficient for most of the year, rødlysterapi, nær-infrarød, and particularly deep infrared during mørketid. That makes proper dosing in winter sessions genuinely significant, not just academically interesting. If you are relying on your panel to compensate for the mitochondrial load of months of low-quality light, getting the distance and the skin exposure right is not a minor detail. It is the whole point.
I use my panel at 15 to 20cm, bare skin, most mornings. That's not because I am obsessive about protocol, though maybe I am a bit. It's because I understand what the mechanism requires, and cutting corners on irradiance or skin exposure means the mitochondria never receive the signal I'm trying to send them.
The near-field geometry of a large panel does give you some forgiveness. Moving from 15cm to 25cm is not catastrophic the way a pure inverse square calculation would suggest. But that forgiveness evaporates by 50cm, and it is essentially gone by 1.5m.
The Practical Summary
Bare skin, close distance (10 to 30cm for most panels), sufficient session time to accumulate at least 3 to 6 J/cm² at tissue depth. That is PBM. That is what the research was testing. That is what the mechanism requires.
Clothes on, standing a metre and a half back, experiencing a general warm red glow? That is something else. Call it light therapy, colour therapy, ambient photostimulation. It may still have value. But do not confuse it with photobiomodulation, and do not expect the specific mitochondrial effects that the clinical literature describes.
The panel is not magic. The physics is not flexible. The mechanism requires that the photons actually arrive at the chromophore, in sufficient numbers, at the right wavelengths, with enough energy to drive an electron transition. Everything between the LED and that chromophore is attenuation. Minimise it.
If you want to explore the full range at lighttherapy.no, you will find panels specified with measured irradiance at stated distances, because that is the only number that is actually useful: red light panels. If you want a portable option that makes close-distance use genuinely easy — on a specific joint, for example, or while travelling — the portable devices collection is worth a look. And if you want to carry the science further, the FAQ page goes into dosing in more detail.
I have also written a related post that covers the clothing question in more practical terms if you want to go deeper on that specific aspect: Does Light Therapy Work Through Clothes?. And if joint pain or muscle recovery is your primary reason for using a panel, the post on infrared light for joint and muscle pain explains exactly why distance and skin exposure matter so much for those specific applications.
Dette innlegget finnes også på norsk: Virker rødlysterapien din egentlig?
FAQ
Does it matter what I wear during red light therapy? Yes, it matters completely. Fabric absorbs and scatters red and near-infrared photons before they reach your skin. Even light-coloured clothing can reduce irradiance at skin level to the point where the primary PBM mechanism, photon absorption by mitochondrial chromophores, cannot occur. Always use bare skin on the area being treated.
How far should I stand from my red light panel? For true photobiomodulation, most consumer panels are most effective at 10 to 30cm. The exact optimal distance depends on the panel's output and dimensions. The inverse square law overpredicts irradiance loss for large LED panels at close range, but by 1.5m most panels are delivering irradiance comparable to ordinary indoor light, which is insufficient for deep-tissue PBM.
Does the inverse square law apply to LED panels? Not strictly, no. The inverse square law applies to point sources. A large LED panel is an extended planar source, and irradiance drops off more slowly than the inverse square law predicts at close distances. However, at distances beyond roughly 50 to 100cm from most consumer panels, the physics converges toward point-source behaviour and the drop-off accelerates. Always use manufacturer-measured irradiance at your actual treatment distance rather than calculating from the inverse square law.
What is the difference between PBM and light therapy? Photobiomodulation (fotobiomodulasjon) is a specific photochemical process where photons of defined wavelengths are absorbed by chromophores inside cells, primarily cytochrome c oxidase in the mitochondria, triggering specific biological cascades including ATP synthesis and nitric oxide release. Light therapy in the broader sense refers to any health application of light, including SAD lamps, blue light therapy for skin, and circadian lighting. PBM requires specific wavelengths, sufficient irradiance at tissue depth, and bare skin. General light therapy operates primarily via retinal and neuroendocrine pathways and does not require the same precision.
Trenger jeg bar hud for rødlysterapi? (Do I need bare skin for red light therapy?) Ja. For at fotobiomodulasjon skal virke, må fotonene nå mitokondrier i vevet under huden. Klær absorberer og sprer fotonene før de når huden. Selv lyse klær kan redusere irradians nok til at den primære mekanismen ikke fungerer.
Hvor nærme må jeg stå panelet for at det skal virke? (How close do I need to stand to the panel for it to work?) For de fleste forbrukerpaneler gir 10 til 30 cm best resultat. Omvendt kvadratlov gjelder ikke fullt ut for store LED-paneler på nært hold, men ved 1,5 m er irradiansen vanligvis for lav for dyp fotobiomodulasjon.
The information in this post is educational and intended for general wellness purposes. It is not medical advice. Always consult a qualified healthcare provider before starting any new health protocol, particularly if you have an existing condition or are taking medication.
References: Hamblin, M.R. (2016). Photobiomodulation or low-level laser therapy. Journal of Biophotonics, 9(11-12), 1122-1124. Chung, H. et al. (2012). The nuts and bolts of low-level laser (light) therapy. Annals of Biomedical Engineering, 40(2), 516-533.