Your cells are listening to light

Sit in sunlight and your skin warms, your mood shifts — those effects are obvious. What is far less obvious is that certain wavelengths of light are doing something stranger and more specific: interacting with the energy-producing machinery inside individual cells, altering how much ATP they generate within seconds of exposure.

This happens because biological tissue is semi-transparent across a narrow band of the electromagnetic spectrum — roughly 600 to 1,100 nm, spanning visible red through to near-infrared. Below that window, shorter wavelengths scatter or are absorbed at the surface; above it, water in tissue drinks them up before they travel far. In the gap sits what researchers call the optical or therapeutic window: the frequencies that can actually reach living cells in meaningful quantities.

Professor Paul Lee — orthopaedic surgeon, biomedical engineer, and author of Regeneration by Design — argues that this is not a curiosity but a lever. As a clinician who studies how physical energy modalities interact with tissue repair, he places light within the Physics pillar of his four-part framework: one of the forces we can apply deliberately to design vitality rather than accept decline.

So what, precisely, is happening inside the cell when that light arrives?

The protein that acts as a light receptor

The answer begins with a single protein: cytochrome c oxidase (CCO), the terminal enzyme of the mitochondrial electron transport chain. CCO is a metalloprotein — its active sites contain copper and iron centres whose electrons shift state when they absorb a photon. Because this reaction depends on matching photon energy to the specific absorption bands of those metal centres, it is wavelength-selective: the effect is photochemistry, not the generic warming that any infrared source can produce.

Think of CCO as a valve governing the final step of cellular energy production. Under normal conditions it runs freely, allowing electrons to flow down the chain and driving ATP synthase. But in metabolically stressed or ageing cells, a different molecule gets in the way: nitric oxide (NO). NO binds to the same copper site on CCO that oxygen normally occupies, partially blocking the chain — a competitive throttle that suppresses ATP output without killing the cell outright.

This is where incoming red and near-infrared photons act as the first domino. Research by Hamblin (2018) and de Freitas & Hamblin (2016) establishes that photons in the 600–1,100 nm range carry sufficient energy to break the NO–CCO bond, freeing the site for oxygen and allowing electron transport to resume. Stressed or ageing cells benefit disproportionately precisely because they carry the greatest NO burden — the valve is most stubbornly stuck in the people who most need it open.

The mitochondrial charging event

Once that bond breaks, the chain reaction is rapid and sequential.

With the copper site clear, oxygen reclaims its position and electrons flow again through Complexes I to IV. Protons are pumped across the inner mitochondrial membrane, rebuilding the electrochemical gradient — the mitochondrial membrane potential (Δψm) — which drives ATP synthase (Complex V) like water through a turbine. Cellular ATP levels rise within seconds to minutes of light exposure: this is the mitochondrial charging event, a near-immediate bioenergetic response rather than the slow hormonal shift that follows exercise or sleep.

Two further effects reinforce it. Light- and heat-gated ion channels open independently of CCO, admitting a controlled influx of calcium (Ca²⁺). Calcium is a prolific second messenger: its arrival triggers proliferative and repair cascades that run in parallel with the ATP-driven recovery, reinforcing the overall regenerative signal. Separately, the re-engaged electron transport chain releases a modest quantity of reactive oxygen species (ROS). At these low concentrations — quite different from the damaging oxidative stress associated with ageing — ROS act as signalling molecules, activating transcription factors that upregulate genes for protein synthesis, anti-inflammatory mediators, and anti-apoptotic proteins. Hamblin (2018) and de Freitas & Hamblin (2016) describe this as a shift in cellular redox state that effectively wakes up dormant repair programmes.

Three distinct downstream effects, then, from a single upstream unlock: energy restored, repair cascades switched on, and gene expression redirected — all within the span of a brief session.

What happens beyond the mitochondria

Beyond the mitochondria itself, two molecules carry the effects outward into surrounding tissue.

The nitric oxide released from CCO does not stay inside the cell. It diffuses into adjacent tissue and signals smooth muscle in capillary walls to relax, widening local blood vessels and improving microcirculation to the treated area — a vasodilatory effect that runs separately from, and in parallel with, the intracellular energy events already described.

Simultaneously, the rise in ATP reaches fibroblasts — the cells responsible for producing structural proteins in the dermis. Hamblin (2018) and de Freitas & Hamblin (2016) document activation of these cells in response to photon-driven signalling; sustained use over 8–12 weeks is associated with improved collagen density, a finding most directly relevant to the 660 nm red-light band that reaches the dermis.

A third ring of effect involves stem and progenitor cells, which appear particularly responsive to the PBM-driven shift in mitochondrial redox state. This is where the science connects naturally to the framing in Professor Paul Lee's Regeneration by Design: the body already houses the repair architecture; photon-driven signalling may help activate it. These effects accumulate in sequence — microvascular improvement, fibroblast activity, and stem-cell mobilisation each unfolding on different biological timescales — which is why research protocols typically run over a 4–12 week loading phase of 3–5 sessions per week rather than concentrating exposure into a single large dose.

Red vs near-infrared: which wavelength reaches where

Depth, not just wavelength, determines which tissues benefit — and the two bands used in photobiomodulation occupy very different physical territories inside the body.

Red light at 660 nm penetrates approximately 1–5 mm, reaching the epidermis, dermis, and the superficial connective tissue just beneath. This is the band most relevant to skin-layer activity: the fibroblast activation and collagen changes described in the previous section occur precisely because 660 nm photons can reach the cells that produce them. Go deeper, and red light is absorbed before it arrives.

Near-infrared at 850 nm travels a different distance altogether — roughly 20–50 mm into tissue, bringing it into contact with muscle fibres, tendons, joint capsules, and bone. The longer wavelength scatters less and penetrates further, making it the primary band for musculoskeletal and deep-tissue recovery support.

These ranges are approximate. Skin tone, tissue density, and device output all affect real-world depth; they are useful guidance rather than precise measurements.

The practical implication is that neither wavelength alone covers the full range of targets. The 660/850 nm combination has become the standard dual-band configuration in both research settings and consumer devices for exactly this reason — surface and depth addressed in a single session. The Regen PhD Pod's CellLight™ system applies this same pairing, calibrated to keep both wavelengths within the biostimulatory dose window described in the Arndt-Schulz biphasic curve, supporting both surface-layer regeneration and deeper tissue recovery.

A practical weekly protocol

The dose curve cuts both ways. At low-to-moderate fluence — roughly 3.7–5 J/cm² — photons drive the mitochondrial events described earlier: NO dissociation, restored electron transport, elevated ATP. Push past that threshold and the same light begins to suppress the very pathways it first activated. Huang et al. (2009, 2011) call this bioinhibition: the Arndt-Schulz curve bends downward, and longer or more frequent sessions can reverse the gains rather than extend them.

That single fact reshapes how to approach a weekly protocol. More is not better; consistent is.

Loading phase (weeks 1–12): Three to five sessions per week, 10–20 minutes per targeted area, device roughly 6–12 inches from skin. Allow 24–48 hours between deep-tissue (NIR) sessions — not an arbitrary rest rule, but a reflection of mitochondrial biogenesis timelines: the repair cascades set in motion by each session need time to resolve before the next stimulus arrives.

Maintenance: Once adaptation stabilises, typically after an 8–12 week loading block, one to three sessions weekly may sustain the signal.

Timing: Pre-exercise application (two to three hours before training) may prime mitochondrial output for the session ahead. Post-exercise use is associated with lower creatine kinase levels and reduced muscle soreness. Pre-sleep sessions may support parasympathetic down-regulation — a useful complement to sleep-focused protocols.

These are starting parameters, not fixed prescriptions. Individual response varies with tissue type, skin tone, and device output. Professor Paul Lee's Practical Regeneration (FCM Publishing, 2026) provides the device-specific depth and protocol context that general ranges cannot fully replace.

What separates PBM from most recovery inputs is precisely this dose constraint. Inadequate sleep, a missed meal, or skipped movement generally fail by absence — they withhold a stimulus. Excess light dosing can actively undo the adaptation it was meant to produce. So if response appears to plateau early, the evidence-informed first move is to reduce session frequency, not increase it. That is a rare instruction in the wellness space, and an honest one.

The information above is for general wellness purposes only. Anyone with specific health conditions should consult a qualified healthcare professional before beginning a light therapy practice.

1. [1] Low-level laser therapy — Wikipedia. https://en.wikipedia.org/?curid=18252764 https://en.wikipedia.org/?curid=18252764
2. [2] Cytochrome c oxidase — Wikipedia. https://en.wikipedia.org/?curid=96842 https://en.wikipedia.org/?curid=96842