810nm Near-Infrared: Brain & Deep Tissue

If red light at 630–670nm is the wavelength range for skin and surface tissues, 810nm is the wavelength for the brain. Sitting in the near-infrared (NIR) spectrum — invisible to the human eye — 810nm has become the most studied wavelength for transcranial photobiomodulation (tPBM), with published research on traumatic brain injury, depression, Alzheimer’s disease, and cognitive enhancement.

What makes 810nm special is not its interaction with cytochrome c oxidase, which it shares with other PBM wavelengths, but its ability to penetrate deep into tissue — including through the human skull. This article examines the physics behind that penetration, the key clinical studies, how 810nm compares to its neighbours at 830nm and 850nm, and which devices deliver this wavelength.

Why 810nm Penetrates So Deeply

The Optical Window

Tissue penetration by light depends on a balance between absorption and scattering. The main absorbers in biological tissue are water, haemoglobin (oxygenated and deoxygenated), and melanin. Each of these has a characteristic absorption spectrum:

• Haemoglobin absorbs strongly below 600nm, with absorption decreasing as wavelength increases through the red and into the near-infrared
• Water absorbs strongly above 1000nm, with a significant absorption band beginning around 970nm
• Melanin absorbs broadly across the visible spectrum, decreasing with increasing wavelength

Between approximately 650nm and 950nm, there is a relative minimum in absorption by all three chromophores. This zone is called the “optical window” or “therapeutic window” of tissue (Smith, 2005; PMID: 16258530). Within this window, 810nm sits near the sweet spot — haemoglobin absorption has dropped significantly, and water absorption has not yet risen. The result is that 810nm photons can travel further through tissue than almost any other wavelength.

Penetration Through the Skull

The human skull presents a significant barrier to light. It consists of cortical bone, diploe (spongy bone), and the meninges beneath. Jagdeo et al. (2012; PMID: 23086162) measured transcranial light penetration using cadaveric human skulls and found that near-infrared light at 810nm penetrated the skull significantly better than red light at 660nm. Approximately 2–3% of 810nm light reached a depth of 2–3cm through the temporal bone, with lesser penetration through the thicker frontal and parietal bones.

Tedford et al. (2015; PMID: 25915476) used sheep heads to model transcranial light delivery and found that 808nm light could reach the brain surface at therapeutically relevant intensities when applied at the temporal region or forehead. The penetration was sufficient to achieve irradiances in the mW/cm² range at the cortical surface — within the range shown to produce biological effects in cell and animal studies.

Henderson and Morries (2015; PMID: 26076815) used high-power (10–15W) 810nm and 980nm lasers in a clinical protocol and measured 0.45% transmission through the human skull, achieving approximately 20–30 mW/cm² at the brain surface. This confirmed that, with sufficient power, therapeutically relevant doses can be delivered to the brain transcranially.

The Brain Wavelength: Key Clinical Studies

Traumatic Brain Injury (TBI)

810nm is the most studied wavelength for TBI, with evidence spanning from animal models to human case series and early randomised trials.

Naeser et al. (2014; PMID: 24568233) published a landmark case series of 11 chronic TBI patients treated with transcranial LED arrays at 810nm and 660nm. Patients received 18 sessions over 6 weeks, with treatments applied to the forehead and temporal regions. Neuropsychological testing revealed significant improvements in executive function, verbal learning, and memory. These improvements were sustained at follow-up assessments months after treatment ended.

Naeser’s work is notable because her patients were chronic TBI cases — months to years post-injury — where spontaneous recovery would not be expected. The improvements were measured on standardised neuropsychological tests, not subjective self-report, lending credibility to the findings.

Morries et al. (2015; PMID: 26076815) treated 10 chronic TBI patients with high-power 810nm laser applied transcranially. Using a 10W laser to ensure adequate brain penetration, they reported significant improvements in depression scores, headache severity, sleep quality, and cognition. All 10 patients showed measurable improvement on at least one outcome measure.

In animal models, Oron et al. (2006; PMID: 16483689) demonstrated that a single transcranial application of 808nm laser in rats after induced traumatic brain injury significantly reduced neurological deficit scores at 28 days post-injury compared to controls. Histological analysis showed reduced lesion size and improved neuronal survival in the treated group.

Alzheimer’s Disease and Dementia

Saltmarche et al. (2017; PMID: 28211344) published a case series of 5 patients with moderate-to-severe dementia treated with transcranial and intranasal PBM using 810nm LEDs. Over 12 weeks of home treatment (three sessions per week), caregivers reported improvements in cognitive function, including better orientation, recognition of family members, and reduced anxiety. Mini-Mental State Examination (MMSE) scores improved in 4 of 5 patients.

Berman et al. (2017; PMID: 28186867) conducted a pilot randomised controlled trial using transcranial PBM at 810nm in patients with dementia. The active treatment group showed trends toward improvement in cognitive measures compared to the sham group, though the small sample size (n=11) limited statistical power.

The rationale for PBM in Alzheimer’s disease centres on mitochondrial dysfunction. Amyloid-beta accumulation impairs mitochondrial function in affected neurons, reducing ATP production and increasing oxidative stress. By restoring CCO activity and boosting ATP synthesis, 810nm PBM may provide a metabolic rescue — keeping neurons functional for longer even in the presence of amyloid pathology (Hamblin, 2019; PMID: 30346890).

Major Depressive Disorder

Cassano et al. (2016; PMID: 26989758) reviewed the rationale for transcranial PBM in depression and conducted a pilot open-label study using 810nm laser applied to the forehead (targeting the dorsolateral prefrontal cortex). Participants showed significant reductions in Hamilton Depression Rating Scale (HAM-D) scores after 6 weeks of twice-weekly treatment. The proposed mechanism involves improving mitochondrial function in prefrontal cortex neurons, increasing cerebral blood flow, and modulating cortical excitability.

Cassano et al. (2018; PMID: 29130996) followed up with a larger study confirming safety and demonstrating a dose-response relationship — higher total fluences correlated with greater improvement in depression scores. A sham-controlled randomised trial is underway.

Schiffer et al. (2009; PMID: 19684191) had earlier demonstrated that a single session of 810nm LED applied to the forehead produced significant improvements in mood, measured by the Hamilton Depression and Anxiety Rating Scales, within two weeks. They also measured cerebral blood flow changes using functional near-infrared spectroscopy (fNIRS), confirming that the light was reaching and affecting the prefrontal cortex.

Stroke

Lampl et al. (2007; PMID: 17395058) conducted the NEST-1 trial (NeuroThera Effectiveness and Safety Trial), a randomised, double-blind, sham-controlled study of transcranial 808nm laser therapy for acute ischemic stroke. 120 patients were treated within 24 hours of stroke onset. At 90 days, the treated group showed significantly better outcomes on the National Institutes of Health Stroke Scale (NIHSS) compared to the sham group.

However, the subsequent NEST-2 trial (Zivin et al., 2009; PMID: 19789381), a larger Phase III study with 660 patients, failed to reach its primary endpoint — though subgroup analysis suggested benefit in moderate (but not severe) stroke patients treated within 14 hours of onset. The NEST-3 trial was terminated early for futility based on interim analysis.

The stroke trials illustrate an important lesson: promising early results do not always survive rigorous large-scale testing. The NEST programme’s mixed results do not invalidate 810nm PBM for neurological applications, but they caution against over-interpreting small trials and case series.

810nm vs 830nm vs 850nm

These three near-infrared wavelengths are often discussed interchangeably, but they have distinct properties:

Parameter	810nm	830nm	850nm
CCO absorption	Strong (near NIR peak)	Moderate	Moderate
Water absorption	Very low	Very low	Low (beginning to increase)
Transcranial penetration	Excellent — most studied for tPBM	Good — less studied for brain	Good — more commonly in consumer panels
Clinical brain evidence	Strongest (Naeser, Cassano, Saltmarche, NEST trials)	Limited	Very limited for brain
Consumer device availability	Moderate — found in clinical and some premium panels	Less common	Very common — standard NIR wavelength in panels
Deep tissue penetration	Excellent	Excellent	Very good

The key distinction: 810nm has the strongest evidence base specifically for transcranial and neurological applications. This is partly because the NEST stroke trials, Naeser’s TBI work, and Cassano’s depression studies all used 808–810nm, creating a body of research that does not yet exist for 830nm or 850nm in brain applications.

For non-brain deep tissue applications (joint pain, muscle recovery), the differences between 810, 830, and 850nm are likely clinically insignificant. All three wavelengths activate CCO, penetrate deeply, and fall within the optimal NIR range. Most consumer panels use 850nm because the LED chips are widely available and well-characterised.

If your primary interest is transcranial PBM for cognitive health, TBI recovery, or mood, 810nm is the most evidence-supported choice. If you want a general-purpose NIR wavelength for deep tissue, 850nm is a perfectly valid alternative with the widest device selection.

Devices Offering 810nm

810nm is less commonly found in consumer devices than 850nm, but it appears in several categories:

• Clinical transcranial devices — Purpose-built tPBM devices like the Vielight Neuro series use 810nm specifically because the neurological evidence base supports this wavelength. These are typically more expensive than general-purpose panels.
• Multi-wavelength panels — Premium panels from manufacturers like PlatinumLED (BIO series) include 810nm as part of a 5-wavelength configuration alongside 630nm, 660nm, 850nm, and occasionally 940nm. These panels allow users to select wavelengths or run all simultaneously.
• Handheld clinical lasers — Several medical-grade handheld lasers used by physiotherapists and sports medicine practitioners operate at 808–810nm. These tend to be higher power (Class 3B or Class 4) and are not consumer products.
• Nasal and ear clip devices — Some transcranial PBM protocols include intranasal light delivery at 810nm, targeting the brain through the thin nasal mucosa. The Vielight 810 intranasal device is the most studied example.

When choosing a device for transcranial use, irradiance is critical. The skull attenuates approximately 97–99% of incident light. A low-power device at 810nm will not deliver therapeutically relevant doses to the brain. Clinical studies used devices delivering 50–250 mW/cm² at the scalp surface to achieve adequate transcranial delivery. Some protocols used high-power (10W+) clinical lasers.

Dosing for 810nm

Transcranial PBM Protocol (Based on Published Studies)

• Wavelength: 808–810nm
• Irradiance at scalp: 50–250 mW/cm² (varies by study and device)
• Target fluence at scalp: 10–60 J/cm² per treatment site
• Estimated cortical irradiance: 1–5 mW/cm² (after skull attenuation)
• Treatment sites: Forehead (prefrontal cortex), temporal regions, midline (default mode network)
• Duration per site: 1–10 minutes (depends on device power)
• Frequency: 2–3 sessions per week in most published protocols
• Treatment course: 6–12 weeks in clinical studies

Deep Tissue / Joint Applications

• Irradiance: 50–100 mW/cm² at the skin surface
• Fluence: 6–12 J/cm² (higher than surface protocols because tissue attenuation reduces the dose reaching the target)
• Treatment time: Calculated from irradiance and target dose
• Frequency: 3–5 times per week

As with all PBM applications, the biphasic dose response applies. More is not better — excessive irradiation at 810nm can inhibit rather than stimulate biological processes (Huang et al., 2009; PMID: 19764898).

Safety Considerations

810nm near-infrared light is invisible — you cannot see it and you cannot feel it at PBM irradiance levels. This creates two safety considerations:

1. Eye safety: NIR light can damage the retina without triggering the blink reflex (which is activated only by visible light). Never look directly into an 810nm LED or laser source. When using transcranial devices positioned near the eyes, ensure the device includes appropriate eye safety measures.
2. Dosing accuracy: Because you cannot feel the light, there is no tactile feedback to indicate whether you are receiving too little, enough, or too much. This makes power density specifications and treatment timing particularly important.

Published transcranial PBM studies have reported no serious adverse events. The most common side effects are mild and transient: headache (usually after the first few sessions), temporary lightheadedness, and difficulty sleeping if treatment is performed late in the evening (Cassano et al., 2016; PMID: 26989758).

Limitations and Honest Assessment

810nm for transcranial PBM is one of the most exciting frontiers in photobiomodulation research. However, it is important to be realistic about the current state of evidence:

• Most human studies are case series, pilot trials, or small RCTs. Large, multi-centre, sham-controlled Phase III trials are lacking for TBI, depression, and Alzheimer’s disease.
• The NEST stroke trials — the only large-scale RCTs for transcranial 810nm — produced mixed results. Phase III failed to meet its primary endpoint.
• Home-use transcranial devices have not been validated in the same rigorous trials as clinical protocols. The Vielight devices have some published data, but independent replication is limited.
• Individual variation in skull thickness, hair density, and skin pigmentation affects transcranial light delivery. A protocol that works for one person may deliver a subtherapeutic dose to another.

The science is genuine. The mechanism is plausible and supported by animal models and early human data. But transcranial PBM at 810nm is not yet an established medical treatment — it is a promising therapy in the evidence-building phase.

Summary

810nm near-infrared light is the best-studied wavelength for transcranial photobiomodulation. Its position in the optical window — between the absorption peaks of haemoglobin and water — allows it to penetrate deeper into tissue than any red wavelength, including through the human skull to reach the brain at therapeutically relevant intensities.

Key clinical studies by Naeser (TBI), Cassano (depression), and Saltmarche (Alzheimer’s) have demonstrated measurable improvements in cognitive function, mood, and neurological outcomes following transcranial 810nm treatment. The NEST stroke trials produced mixed but partially positive results at Phase II, though Phase III did not succeed.

For anyone interested in brain health, cognitive optimisation, or TBI recovery, 810nm is the wavelength with the most direct supporting evidence. For general deep-tissue applications — joint pain, muscle recovery — 810nm works well, though 850nm provides comparable effects and is more widely available in consumer devices.

The field is still maturing. Larger trials are needed, dosing optimisation continues, and the devices available to consumers are not always validated against clinical protocols. But 810nm represents the leading edge of PBM research, where the potential applications are as deep as the tissue it can reach.

References

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