Photobiomodulation
Light can be a biological signal — if the dose is right
Photobiomodulation, or PBM, uses specific wavelengths of red and near-infrared light to influence cellular function.
It is often marketed simply as “red light therapy”, but that description misses the part that matters most.
PBM is a dose-dependent biological treatment.
The wavelength, intensity, treatment distance, exposure time, treatment area and interval between sessions all influence what happens in the tissue.
The aim is not to deliver as much light as possible.
It is to deliver the right light, to the right tissue, at the right dose.
What actually happens when light reaches a cell?
The old explanation of PBM was fairly simple:
light → mitochondria → more ATP
That remains part of the story, but we now understand that the biology is considerably richer.
Red and near-infrared photons can interact with mitochondrial chromophores such as cytochrome-c oxidase, but mitochondria are not the only potential light sensors. Opsins, ion channels and other cellular chromophores may also contribute to the response.
The first photochemical changes can then trigger a wider signalling cascade involving:
- mitochondrial electron transport
- ATP production
- nitric oxide
- controlled reactive oxygen species signalling
- calcium signalling
- intracellular kinase pathways
- transcription factors
- changes in gene expression
The important point is that PBM is not simply “charging the mitochondria”.
It is using light to influence cellular signalling.
The wavelength matters
Not all light behaves in the same way.
Different wavelengths are absorbed and scattered differently as they pass through tissue. They also interact with different cellular photoreceptors.
For clinical PBM, I am particularly interested in the red and near-infrared range.
Common wavelengths in the devices I use include:
630 nm | 660 nm | 810 nm | 830 nm | 850 nm | 1064 nm
Red wavelengths tend to be useful for more superficial targets.
Near-infrared wavelengths penetrate more deeply and are therefore particularly relevant when the target is muscle, nerve, thyroid tissue, joints or the brain.
The relationship is not simply “longer wavelength = better”. Tissue composition, scattering, absorption and the biological target all matter.
More is not always better
One of the most important principles in PBM is the biphasic dose response.
Too little light may produce very little biological effect.
Increase the dose and the biological response may improve.
But once the useful therapeutic window has been reached, more treatment does not necessarily create more benefit.
This is the Goldilocks principle of photobiomodulation.
That does not mean that crossing a specific number suddenly becomes dangerous.
It means that more light is not automatically better therapy.
That is why I do not prescribe PBM as simply “use the panel for 10 or 20 minutes”.
The correct dose depends on the tissue, the device and the biological response we are trying to achieve
Surface dose is not target-tissue dose
This distinction matters enormously in clinical PBM.
The dose delivered at the skin surface can be estimated from the device output and the treatment time.
But deeper tissues do not receive the same dose as the skin surface.
Light is progressively absorbed and scattered as it passes through skin, blood, fat, fascia, muscle, bone and other tissues.
A thyroid gland, peripheral nerve, shoulder capsule or cerebral cortex therefore receives only a fraction of the light measured at the surface.
The number on the device is not necessarily the dose reaching the tissue we are trying to treat.
That is why tissue depth and anatomy have to be considered when designing a PBM protocol.
HOW I BUILD A PBM PRESCRIPTION
A useful PBM prescription is never just a number of minutes.
It requires several interacting decisions:
- wavelength
- irradiance
- treatment distance
- exposure time
- treatment area
- tissue depth
- frequency of treatment
- recovery interval between treatments
Change one of these variables and you may substantially change the treatment.
That is why a 3-minute thyroid protocol, a 45-second hand protocol, and a 20-minute brain protocol can all be entirely appropriate.
They are treating different tissues, with different devices, for different biological aims.
WHERE I USE PBM
PBM is not one treatment with one evidence base.
The quality of evidence varies depending on the condition, the tissue being treated, the device being used and the outcome being measured.
In some areas the human evidence is relatively mature.
In others it is promising but still developing.
I prefer to be clear about that distinction.
Chemotherapy-Induced Peripheral Neuropathy
PBM is an increasingly interesting supportive option for burning, tingling, numbness and altered sensation in the hands and feet caused by chemotherapy.
Hashimoto Thyroiditis
Human studies have explored whether carefully dosed PBM over the thyroid may influence oxidative stress, thyroid structure, autoimmune activity and remaining thyroid function.
Brain Fog, Memory & Cognitive Function
Transcranial and intranasal PBM are being studied for their effects on mitochondrial function, cerebral blood flow, neuroinflammation and cognition.
Movement Disorders
Near-infrared PBM is being investigated in neurological conditions involving altered neural signalling, mitochondrial dysfunction and neuroinflammation.
Depressive Symptoms
Transcranial PBM is also being studied as an adjunctive approach for mood disorders, with proposed effects on brain energy metabolism, blood flow and inflammatory signalling.
Musculoskeletal Pain & Injury
PBM has a broader role in musculoskeletal medicine than many people realise, including osteoarthritis, tendinopathy, joint pain, muscle injury and rehabilitation.
Wound Healing
PBM may support inflammatory regulation, fibroblast activity, collagen production, angiogenesis and tissue repair in selected wounds.
Supportive Oncology
PBM has useful applications in supportive cancer care, particularly for problems such as oral mucositis, neuropathy, treatment-related tissue injury and healing support.
WHAT DOES THE EVIDENCE LOOK LIKE?
It is tempting to talk about “the evidence for PBM”.
In reality, there is no single PBM evidence base.
Some applications have multiple clinical trials and systematic reviews.
Others have small human studies, pilot trials or predominantly mechanistic evidence.
A treatment can be biologically plausible and clinically interesting without yet being proven.
I find it more useful to think in terms of an evidence spectrum:
relatively mature → promising → early / emerging
That distinction matters, especially in a field that is often marketed too confidently.
THE DEVICES I USE
Vielight NeuroDuo 4
The Vielight Neuro Duo is designed specifically for transcranial and intranasal PBM.
I use it for selected neurological applications where the brain is the primary treatment target.
Sohl Midi
The SOHL Midi is better suited to larger treatment areas where broader coverage is needed.
A larger panel is not automatically better. For some problems, the smaller treatment field of the Compact is actually an advantage.
Sohl Compact
The SOHL Compact is useful for targeted treatment of relatively small areas such as hands, feet, thyroid tissue, smaller joints and selected local musculoskeletal problems.
PBM is a tool, not the whole treatment
I would never look at neuropathy, chronic pain, thyroid autoimmunity, cognitive symptoms or poor tissue healing and assume the answer is simply to shine red light at it.
I still want to understand why the problem is there.
Depending on the patient, that may involve looking at nutrition, mitochondrial health, metabolic function, sleep, inflammation, medications, hormonal influences, gut health, environmental exposures, neurological disease or the effects of cancer treatment.
PBM may help the tissue.
The broader clinical work is about understanding the terrain.
Could photobiomodulation have a role for you?
If you are interested in PBM but are unsure whether it is appropriate, which device to use or what treatment protocol makes sense, this can be assessed as part of a Functional Medicine consultation.
I can help determine:
- whether PBM has a reasonable role
- what tissue should be targeted
- which device is most appropriate
- what dose to use
- how often to treat
- what should be monitored