<p>Red light therapy is the exposure of skin to low-power red and near-infrared light, roughly between 600 and 950 nanometres. Its scientific name is <strong>photobiomodulation</strong>. That is the whole definition. Everything added to it — UV, heat, tanning, medical lasers — belongs to a different technology.</p>
<p>This article sets out the basics, and above all what they exclude. It is the first of four on the principles of red light.</p>
<h2>What actually happens under the skin</h2>
<p>The chain has four steps, and none of them asks you to take anything on faith.</p>
<p><strong>The photon crosses the skin.</strong> Between 600 and 950 nm, haemoglobin and water absorb little light: this is what physicists call the optical window of living tissue. Below that range, blood absorbs almost everything; above it, water takes over. The window was not chosen by a marketing department, it is a physical constraint.</p>
<p><strong>An enzyme absorbs it.</strong> The identified photoacceptor is cytochrome c oxidase, the last link of the respiratory chain, inside the mitochondrion. Its copper and haem centres absorb precisely in the red and near-infrared.</p>
<p><strong>Nitric oxide lets go.</strong> Under stress, that molecule binds to the enzyme and slows electron transport. The leading hypothesis is that the photon displaces it. Once released, it also dilates blood vessels — hence the flush you see during a session.</p>
<p><strong>ATP rises.</strong> Electron transport resumes, cellular energy production increases, and signalling cascades switch on. It is at this level, and not before, that the effects measured in clinical trials become plausible.</p>
<p>The full chain, with the reference reviews that describe it, is on <a href="/en/pages/comment-ca-marche">how it works</a>.</p>
<h2>Four confusions to clear up</h2>
<h3>It is not UV</h3>
<p>Ultraviolet stops at 400 nm. The shortest spectrum used in a consumer light therapy device is a 460 nm blue, and most of the work happens between 590 and 940 nm. So there is no tanning and no UV-related photocarcinogenic risk. It is the exact opposite of a tanning bed, which relies on wavelengths shorter than visible light.</p>
<h3>It is not heat</h3>
<p>An infrared sauna heats you. A red light therapy device does not have heat as its purpose: the warmth you feel at close range comes from the LEDs themselves, not from an intended effect. The confusion is kept alive by devices that do both — and then you need to know which of the two you are buying.</p>
<h3>It is not a medical laser</h3>
<p>A large share of the historical scientific literature uses a low-power laser rather than LEDs. The two are not interchangeable: a laser delivers coherent light over a small area, an LED diffuse light over a wide one. What that changes in how the studies should be read is detailed on <a href="/en/pages/science">the Science page</a>, where the light source is stated for every paper cited.</p>
<h3>It is not a treatment</h3>
<p>A home red light therapy device is a wellness product. It does not diagnose, treat or cure any disease, and any brand telling you otherwise is exposing you as much as itself. If you have symptoms, an ongoing treatment or are pregnant, a healthcare professional's advice takes precedence over any web page, including this one.</p>
<h2>Where the evidence stands</h2>
<p>The level of evidence is not the same depending on what is being measured, and that is the thing most pages in this industry forget to say.</p>
<p>It is strongest for pain: sixteen randomised trials and 820 patients gathered in a meta-analysis published by <em>The Lancet</em> in 2009, with adverse effects no different from placebo. It is strong too for muscle recovery and performance, where several meta-analyses converge.</p>
<p>It is markedly thinner elsewhere. The most-cited trial on sleep covers twenty athletes over fourteen days: that is a signal, not a proof, and we write it that way. On chronic wounds, a systematic review of six LED trials published in 2026 grades the evidence as very low under GRADE.</p>
<p>The domain-by-domain detail, with the sample size of every trial, is on <a href="/en/pages/benefits">the benefits page</a>.</p>
<h2>What to take away before buying</h2>
<p>Three things, and they fit in three sentences.</p>
<p>Wavelength decides which area is reached: that is the subject of the <a href="/en/blogs/news">next article</a>. Dose decides the effect, and stronger is not better. And consistency decides everything else — a device you do not use has an efficacy of zero, whatever its nanometres.</p>
<p>None of the studies cited here was run on an Antared device. We run no clinical trials: we set our devices to the parameters published in this literature, and we display those parameters on every product page so that you can compare them.</p>