Let There Be Light

Before there were supplements, before there was surgery, before there was even food as medicine — there was light. For hundreds of thousands of years, human biology evolved under a very specific sequence: the warm glow of sunrise, the full-spectrum intensity of midday, the long red and amber tones of sunset, then darkness. The pattern repeated with the precision of a clock, because it was the clock.

We have changed that environment more profoundly in the last hundred years than in all of human history before it. We have replaced the full solar spectrum with narrow-wavelength artificial light. We flood our eyes with blue-shifted LEDs at midnight. We work night shifts, sleep in lit rooms, and spend our days under fluorescent tubes that bear no more relationship to sunlight than a vending machine does to a vegetable garden. And we are paying for it — in ways the research is only now beginning to document.

This is an article about light. About what our biology requires from it, what happens when we are deprived of it, and about the rapidly growing field of photobiomodulation — the clinical use of specific light wavelengths to restore, repair, and heal. It is also about the difference between the LED bulb in your ceiling and the LED therapy device NASA-derived research helped create. They are not the same thing. Not even close.

The Spectrum of Sunlight: A Complete Biology Lesson

Sunlight is not one thing. It is a layered spectrum of electromagnetic radiation, each wavelength interacting with human biology in its own distinct way.

Ultraviolet (UV, 100–400nm) — the shortest visible wavelengths, best known for driving vitamin D synthesis in the skin and for their germicidal properties. UV-A (315–400nm) penetrates more deeply and is involved in melanin production; UV-B (280–315nm) triggers vitamin D conversion and can cause sunburn in excess.

Visible light (400–700nm) — the rainbow the eye perceives. Blue light (400–490nm) suppresses melatonin and drives alertness; powerful and necessary at the right time, disruptive at the wrong one. Green light (490–560nm) is the wavelength most efficiently absorbed by melanopsin, the photoreceptor responsible for circadian regulation. Red light (620–700nm) penetrates deeper into tissue and is, as we will see, biologically active in ways that have nothing to do with vision.

Near-infrared (NIR, 700–1440nm) — invisible to the human eye, but deeply biologically active. NIR penetrates the skin, muscle, and even bone. It is abundant in sunlight, particularly at sunrise and sunset, and it sits at the heart of photobiomodulation therapy.

Each morning, the rising sun delivers a specific sequence: first infrared and red wavelengths, then as the sun rises higher, the full spectrum including UV and blue light. This sequencing matters. It is not arbitrary. The red and infrared that arrive first are, researchers now believe, a biological primer — preparing the mitochondria for the more intense wavelengths that follow. Stripping the sequence and replacing it with flat, blue-shifted artificial light all day, and then more of the same at night, disrupts biology at a cellular level.

Inside the Cell: The Mitochondrial Conversation

To understand why light has therapeutic potential, you need to understand what happens when specific wavelengths meet living tissue. Every cell in the body contains mitochondria — the organelles responsible for producing ATP, the molecule that powers virtually every biological process. The health of your mitochondria is, in a very real sense, the health of your body.

Within the mitochondrial respiratory chain, there is an enzyme called cytochrome c oxidase (CCO). It sits at the terminal end of the electron transport chain, catalysing the reduction of oxygen to water and driving the proton gradient that powers ATP synthesis. One research team has called it the engine of the engine.

What makes CCO remarkable in this context is that it is a chromophore — it absorbs light. Specifically, it absorbs wavelengths in the red (600–700nm) and near-infrared (700–1000nm) range. When photons in these wavelengths are absorbed by CCO, a cascade of downstream effects begins: increases in ATP, a brief burst of reactive oxygen species, elevated nitric oxide, modulation of intracellular calcium. Tertiary effects include the activation of transcription factors linked to cell survival, proliferation, migration, and new protein synthesis.

One mechanism deserves particular attention. Under conditions of cellular stress, hypoxia, or damage, nitric oxide binds to CCO and effectively inhibits its function — slowing energy production at precisely the moment it is most needed. Photons absorbed by CCO in the red and near-infrared bands can dissociate this inhibitory nitric oxide, triggering a surge in mitochondrial membrane potential, enhanced oxygen consumption, intensified glucose metabolism, and amplified ATP production. Damaged, stressed, or underperforming cells receive a precise energetic signal to recover.

The Light-First Hypothesis

Among the voices pushing hardest against conventional medicine's near-total neglect of light biology is Dr Jack Kruse — a practising neurosurgeon and self-described quantum biologist who has spent years arguing that light is the primary determinant of human health, with diet and supplements playing a far secondary role.

Kruse describes our evolutionary transition as one fundamentally tied to light — from furry ground-dwelling mammals to upright-walking primates, with the critical role of the POMC gene, melanin, and the function of mitochondria as producers of endogenous light. He frames the distortion of our modern light environment as the key underlying driver of modern chronic disease.

His core argument: our mitochondria are sensitive to light, and when we receive natural light — especially morning light — we are feeding our biology the signals it needs to regulate hormones, repair tissues, and reduce inflammation. When that signal is absent or distorted, mitochondrial function degrades. He emphasises the importance of red and UV-A light, which penetrate deeply into the skin and eye, helping reset the body's internal clock — and links this to a production of melatonin that begins in the eye, not, as commonly believed, solely in the pineal gland.

Some of Kruse's claims venture into territory mainstream science has not yet validated, and he remains a polarising figure. But his central contention — that the human body is a light-responsive system evolved under full-spectrum sunlight, and that modern artificial environments constitute a form of chronic biological stress — is increasingly supported by peer-reviewed literature.

Melanin, Melatonin, and the Architecture of Biological Time

Two molecules deserve particular attention when we talk about light and human biology: melanin and melatonin. They are often confused, occasionally conflated, and profoundly different — yet both are light-responsive, and both are central to understanding what happens when our light environment is disrupted.

Melanin is the pigment responsible for skin, hair, and eye colour. It is synthesised primarily in melanocytes and acts as a broadband absorber of UV and visible light, protecting DNA from photodamage. But melanin's role extends far beyond pigmentation. It is also a semiconductor capable of absorbing photons and converting light energy into chemical signals within the skin. The more we understand it, the more it looks like an ancient biological antenna — evolved not just to defend against UV damage, but to transduce the information carried in sunlight into cellular chemistry.

Melatonin, most people know as a sleep hormone — the chemical expression of darkness, produced by the pineal gland when light fades. What is less widely known is how melatonin is also a powerful antioxidant, an immune modulator, and a mitochondrial protector. Its production is far more complex than the simple "dark equals melatonin" narrative suggests.

Evidence shows that near-infrared radiation, which occupies a major portion of the wavelengths of sunlight, may promote melatonin production — and that the beneficial effects of sun exposure or photobiomodulation therapy may be, at least partially, mediated by increased local melatonin production induced by NIR. Unlike visible light, NIR can penetrate deep into the human body, including muscle, brain, and bone.

This is a remarkable finding. The same NIR wavelengths that stimulate mitochondrial function may simultaneously support melatonin production locally within tissues, independent of the pineal gland's nocturnal rhythm. Daytime NIR exposure from the sun may be doing something entirely different to melatonin biology than we thought: not suppressing it, as blue light does, but stimulating a separate, tissue-level protective response.

The eye, of course, is the primary light receptor. The retina contains not only rods and cones for vision, but also intrinsically photosensitive retinal ganglion cells (ipRGCs) containing the photopigment melanopsin, most sensitive to short-wavelength blue light around 480nm. These cells project directly to the suprachiasmatic nucleus in the hypothalamus — the brain's master circadian clock — which governs hormone secretion, body temperature, immune function, and the timing of virtually every biological process. Light entering the eye is not just for seeing. It is for timing.

Blue Light, Red Light, and the Circadian Disruption Crisis

Here is the critical distinction most people are not taught: not all light is biologically equivalent, and timing matters as much as spectrum.

Blue light (around 460–480nm) is a powerful alerting signal. In the morning and at midday, it is biologically appropriate and beneficial — it suppresses melatonin, raises cortisol, sharpens attention, aligns the circadian clock. For most of human history, the only source of intense blue light was the sky. We are now bathed in it around the clock, from overhead LEDs, computer screens, phones, and tablets, regardless of the time of day or night.

A study examining the impact of red and blue LED light on melatonin secretion in healthy adults found that after two hours of evening exposure, blue light maintained strong melatonin suppression while red light allowed natural recovery — a highly significant difference that underscores blue light's disruptive effects on circadian health and highlights red light as a far less disruptive alternative for nighttime environments.

This is the crux of the ambient LED problem. The energy-efficient bulbs lighting our homes and workplaces emit light heavily weighted toward the blue spectrum. They were designed for visibility and energy efficiency, not biological compatibility. The result is that every evening, millions of people are receiving a strong "it is midday" signal from their environment at the precise time their biology is attempting to transition into its repair and recovery phase.

The Critical Difference: Ambient LED vs. Therapeutic Photobiomodulation

This is perhaps the most misunderstood distinction in the entire field. When people hear "LED light therapy," some imagine a red bulb in a bedside lamp; others picture harsh overhead clinic lighting. Neither is accurate. The difference between ambient LED lighting and therapeutic photobiomodulation devices is not aesthetic — it is physical, measurable, and clinically meaningful.

The issue with most LED lighting is not the technology itself but the limited and often imbalanced wavelengths emitted — typically lacking red and near-infrared light. Standard ambient LED and fluorescent lights can disrupt sleep due to blue light and cause discomfort due to flicker. Modern indoor living leaves us with a deficiency in beneficial red and near-infrared light, impacting cellular health.

Therapeutic photobiomodulation devices are engineered around three specific variables:

• Wavelength precision. Therapeutic devices emit tightly controlled wavelengths — typically 630–660nm (red) and 810–850nm (near-infrared) — chosen because they correspond to absorption peaks in cytochrome c oxidase and other cellular chromophores. A standard LED bulb, even a red one, does not deliver these wavelengths at the required specificity.
• Irradiance (power density). The amount of light energy delivered per unit area, measured in milliwatts per square centimetre. Therapeutic effect requires sufficient irradiance to drive photochemical reactions in tissue — typically 20–100 mW/cm². A red mood bulb delivers nowhere near this. A quality therapeutic device does.
• Dose (fluence). Effective PBM follows what researchers call the Arndt-Schulz law: as the dose is increased, a maximum response is reached at some value; beyond that, the response diminishes, and at very high fluences, inhibitory effects are possible. This dose-dependence is a hallmark of genuine photobiomodulation, and entirely absent in ambient lighting.

A red LED bulb in your lamp: no therapeutic effect. A clinical-grade PBM panel at the correct wavelength and irradiance, applied for the correct duration: measurable cellular response. The LED technology is the same. Everything else is different.

Light in the Clinic: From NASA to the Hospital Ward

Photobiomodulation did not begin with consumer wellness products. It began, as many counterintuitive discoveries do, almost by accident. In 1967, the Hungarian physician Endre Mester was attempting to replicate an American experiment using a ruby laser on cancer cells in rats. His laser turned out to be underpowered — too weak to destroy the tumours. What he observed instead was that the wounds healed faster in the laser-exposed animals. He had stumbled onto the therapeutic potential of low-level light entirely by accident.

LED light therapy was later developed by NASA for plant growth experiments in space. Scientists subsequently found it had applications in wound treatment and the prevention of bone and muscle loss — the kind of tissue degradation that occurs in microgravity environments. The realisation that red and near-infrared light could stimulate tissue repair without the heat of traditional lasers opened an entirely new research pathway.

Today, photobiomodulation has progressed from experimental use in tissue repair to rigorously controlled clinical and translational research, with therapeutic potential investigated in conditions ranging from chronic wounds and dermatological disorders to musculoskeletal pain, neurological dysfunction, ocular disease, oncology supportive care, and immune modulation.

A 2025 international consensus from the Journal of the American Academy of Dermatology, assembled by a multidisciplinary panel of 21 experts following systematic literature review and Delphi methodology, concluded that PBM is a safe treatment modality for adult patients, that red light PBM does not induce DNA damage, and that PBM is an effective treatment option for peripheral neuropathy, androgenic alopecia, wound ulcers of multiple aetiologies, decubitus ulcers, and pain.

In neurological medicine, the applications are expanding rapidly. A systematic review of photobiomodulation in the ageing brain found improvements in spatial, episodic, and social memory in animal models — and in healthy older humans, improvements in working memory, cognitive inhibition, and lexical and semantic access. Cognitive benefits have also been documented in Alzheimer's disease and mild cognitive impairment. Investigations are ongoing in Parkinson's disease, traumatic brain injury, and post-concussion syndrome.

Sunlight, COVID, and the Hospital Window

Perhaps the most vivid recent evidence for light's clinical power came from the COVID-19 pandemic — specifically from the work of Dr Roger Seheult at MedCram and the researchers who examined the relationship between sunlight exposure and patient outcomes.

Seheult discussed how near-infrared radiation from sunlight impacts the mitochondria and subsequent oxidative stress and inflammation. Research published in the Journal of Photochemistry and Photobiology showed that COVID-19 patients who received near-infrared radiation via a wearable device had favourable outcomes. More broadly, research found that a higher duration of sunlight exposure was significantly correlated to health maintenance and speedy recovery in most COVID-19 patients, with a highly significant positive correlation between sunlight exposure and lower death rates.

This is consistent with the broader body of evidence on hospital environments and patient recovery. A study in the Journal of Intensive Medicine examining cardiac intensive care units found that patients with access to daylight and window views had hospital stays shortened by up to 16.8 hours. For patients with conditions like delirium or obesity, the difference reached a full day. A separate long-term Korean analysis of more than 33,000 patients found window proximity shortened stays by three days. Patients in rooms with abundant sunlight reported a 22% decrease in the need for pain medications and experienced better mood and improved appetite.

The Price of Night: Shift Work and the Biology of Darkness at the Wrong Time

If light at the right time heals, light — or its absence — at the wrong time harms. Nowhere is this more starkly documented than in the epidemiology of shift work. Approximately 20% of workers in developed countries work outside standard daytime hours. The health data on this population is striking and, in its accumulation, alarming.

Substantial evidence indicates that long-term night shift work is significantly associated with adverse health outcomes including breast cancer, type 2 diabetes, mood disorders, and metabolic syndrome, and contributes to the development and progression of cardiovascular disease. Shift work has been linked to increased prevalence of carotid artery plaque, increased arterial stiffness, and elevated carotid artery intima-media thickness — all suggestive of accelerating atherosclerosis. The elevation of inflammatory markers and DNA damage in shift workers may be linked to their increased progression of coronary artery disease.

The mechanism is circadian disruption. Forcing the body to be active during its biological night, and to sleep during its biological day, uncouples the carefully timed cascade of hormones, metabolic processes, and cellular repair cycles that evolution calibrated to the solar rhythm. Melatonin, which normally rises in darkness and plays a role in cellular repair and tumour suppression, is suppressed during the working night by artificial light. Cortisol, which should rise with morning, is dysregulated. Insulin sensitivity shifts. The repair window shrinks.

This is not a marginal health consideration. The body knows what time it is, and when we override that knowledge consistently, the cost accumulates.

Sunrise as Medicine: The Red and Infrared Morning Primer

One of the most practically actionable insights from light biology is deceptively simple: go outside in the morning. Not to exercise. Not to check your phone. Just to receive the light.

The sun in the first hour after sunrise produces a spectrum dominated by red and near-infrared wavelengths. The shorter, more energetic wavelengths — blue and UV — are filtered by the atmosphere's greater thickness at low sun angles. What reaches you in those early minutes is nature's photobiomodulation session: warm, red-shifted light that stimulates mitochondrial function, moderates melatonin, begins setting the circadian clock, and does so without the melatonin-suppressing punch of midday blue-spectrum intensity.

One-third of the ATP that mitochondria produce comes from the food we eat; the remainder, according to some researchers, results from interactions in our bodies between light, water, and magnetism. Whether or not one accepts that specific ratio, the principle — that light is a metabolic input, not just a signal — is increasingly supported.

Evening light mirrors this. Sunset also provides a red and infrared-dominant spectrum. For most of human history, this was the light that told the body the day was ending and the repair cycle should begin. Replacing it with overhead white LEDs and phone screens sends precisely the opposite message.

Modern Photobiomodulation: What It Is and What It Can Do

Photobiomodulation therapy — also called low-level laser therapy or, more colloquially, red light therapy — is the clinical application of specific wavelengths of light to stimulate biological healing responses. It is non-thermal, meaning it does not work through heat. It is non-ionising, meaning it does not damage DNA. And it is increasingly evidence-based.

Clinical applications with the strongest evidence base include:

Wound healing and tissue repair

Among the most thoroughly documented applications. PBM accelerates healing of chronic wounds, post-surgical incisions, diabetic ulcers, and radiation-induced tissue damage. The mechanism — enhanced ATP production, increased local circulation, reduced inflammation — is well-characterised.

Musculoskeletal pain and injury

Used widely in sports medicine and physiotherapy for tendinopathy, joint pain, muscle recovery, and post-exercise inflammation. Athletes, particularly at elite level, have adopted PBM as a standard recovery tool.

Dermatology and skin health

Red light stimulates fibroblast activity, increasing collagen and elastin synthesis. Effects on wrinkle reduction, skin texture, and the treatment of sun damage are documented and reproducible. PBM is also used clinically for acne, where blue light (415nm) is added to the protocol for its antibacterial effects against C. acnes.

Neurological and cognitive health

Photobiomodulation has expanded from wound healing to applications in brain stimulation, protection, and regeneration. Transcranial PBM — delivering NIR light through the skull — is under serious investigation for Alzheimer's, Parkinson's, traumatic brain injury, and depression.

Hair loss and seasonal affective disorder

PBM is FDA-cleared for androgenic alopecia (pattern hair loss) in both men and women — one of the more established consumer applications. For SAD, light therapy with bright white light in the morning has been a first-line treatment for decades; research is now refining the spectral composition of therapeutic devices for optimal circadian and mood effects.

What to Look For: Quality, Caution, and Context

As with all expanding wellness fields, the photobiomodulation market is a spectrum — from rigorously engineered clinical devices to poorly made consumer gadgets that share little beyond the name "red light therapy." A few principles for navigating it with a holistic lens:

• Wavelength matters. Devices should specify their emission wavelengths. Therapeutic red light is 630–660nm; near-infrared is typically 810–850nm. Combined panels delivering both are more versatile and better researched.
• Irradiance and dose. Clinical efficacy requires sufficient power density. Look for devices with independently verified irradiance measurements. The Arndt-Schulz principle applies: more is not better. Intensity in the range of 20–40 mW/cm² is generally considered both safe and effective.
• Flicker and EMF. Quality devices are engineered to minimise flicker (which causes neurological stress over prolonged exposure) and electromagnetic field output. Worth asking manufacturers about directly.
• Eyes. Near-infrared is invisible; you will not know if it is entering the eye. Most quality devices supply protective eyewear and recommend its use, particularly for facial treatments.
• Contraindications. PBM is not appropriate for everyone in all circumstances. Active malignancy, photosensitising medications, pregnancy, and certain eye conditions warrant medical consultation before use.
• Sunlight first. Before any device, go outside. Morning sunlight — even through cloud cover — provides a depth and breadth of biological signal that no device fully replicates. The device supplements; the sun is the original.

A New Way of Seeing

There is something profound in what light biology is beginning to tell us. The same sunrise your grandmother watched, the same sunset your children marvel at — these are not just beautiful. They are pharmaceutically active events. The light that reaches us at dawn and dusk carries information that every cell in the body is designed to receive and respond to.

We have spent the last century building environments that deny us this. Enclosed offices with no windows, or windows sealed against UV. Night shifts. Screens at midnight. Blue-shifted LEDs that tell every cell in the body it is high noon even as we try to fall asleep.

Photobiomodulation therapy is, in many ways, an attempt to give back what the modern environment has taken away: specific wavelengths of light at a therapeutic dose, delivered at times and intensities the body can use. It is not magic. It is physics meeting biology — and the research, growing year by year, suggests that this conversation between light and living tissue is one of the most important we can have.

Step into the morning light. Watch the sun go down without a screen in your hand. Consider your light environment the way you consider your food environment — with care, curiosity, and the knowledge that what you receive shapes who you become.