Light is not just something we use to see. It is energy, and for billions of years sunlight has been one of the major energy sources shaping biology.
We evolved under a regular light and dark cycle, in a broad-spectrum solar environment rich in wavelengths that now receive very little attention because our eyes cannot see them. Those longer red and near-infrared wavelengths can pass into the body, deposit energy in tissues, and influence one of the most important systems we have: the mitochondria.
Mitochondria run metabolism. They provide the ATP that allows us to move, think, repair tissue, maintain cellular function, and generally get up in the morning. When mitochondria decline, they can drive inflammation, impair energy production, and contribute to many features of ageing.
That is where photobiomodulation, often called red light therapy, becomes interesting. The basic idea is remarkably simple: certain wavelengths of red and near-infrared light can improve mitochondrial efficiency.
https://www.youtube.com/watch?v=2MzKjYjEE1g
Key Takeaways
- Red and near-infrared light between roughly 660 and 900 nm may improve mitochondrial ATP production.
- Short morning exposures appear more effective than prolonged sessions or late-day treatment.
- Animal and early human studies suggest benefits for vision, inflammation, cognition, and blood glucose regulation.
- Daily outdoor time provides broad-spectrum light exposure alongside movement and metabolic benefits.
Table of Contents
- Why Mitochondria Respond to Light
- The Useful Wavelengths: Red Through Near-Infrared
- How Deep Can Red Light Penetrate?
- Red Light Dosage: More Is Not Necessarily Better
- Inflammation, ATP, and Reactive Oxygen Species
- What Animal Studies Suggest About Healthspan
- Red Light and Cognition: Why the Brain Is a Logical Target
- Early Human Research: Vision and Macular Degeneration
- Can Red Light Improve Blood Glucose Control?
- The Problem With Modern Blue-Heavy Lighting
- Practical Ways to Get More Beneficial Light
- Safety, Limits, and Important Caution
- Where Red Light Research Could Go Next
Why Mitochondria Respond to Light
A useful way to think about mitochondrial energy production is as a railway line. Along the line is a respiratory chain, a sequence of molecular stations that pass energy along until ATP is produced at the final stop.
As we age, it is rather like the tracks become distorted. The train still moves, but it moves less efficiently. Mitochria produce less ATP, while the wider cellular system becomes more stressed.
Longer wavelengths of light appear to be absorbed by parts of that mitochondrial machinery. Absorbing this energy can improve the efficiency of the respiratory chain and increase ATP production.
This is not just an abstract idea. With suitable spectroscopy equipment, mitochondrial activity can be observed directly. As their metabolic state changes, their optical properties change too. In a sense, mitochondria change colour as they become more active, rather like how a person becomes flushed after running upstairs.
For a long time, photobiomodulation was difficult to take seriously because the mechanism was not clear enough. That is changing. We now have a much better handle on the relationship between light, mitochondrial activity, ATP, and inflammation, making clinical exploration far more plausible.
The Useful Wavelengths: Red Through Near-Infrared
The wavelengths of greatest interest sit roughly between 660 and 900 nanometres.
- About 660 to 670 nm: deep red light that is visible to the human eye.
- About 850 nm: near-infrared light that cannot be seen but can penetrate more deeply.
- Above roughly 900 nm: light is increasingly absorbed by water, reducing the amount available to interact with deeper biological structures.
There may be particular hotspots within this range, but it is probably not productive to obsess over every individual nanometre. Humans evolved under sunlight, which provides a broad spectrum rather than a single narrow wavelength.
The reason 670 nm became such a common research wavelength was largely historical. Several of the early research groups happened to have devices emitting 670 nm light, so it became the benchmark. But very similar effects can be achieved around 850 nm.
The practical point is simple: getting a broad exposure to red and near-infrared wavelengths is likely more important than chasing one supposedly perfect wavelength.
Sunlight Has a Natural Balance
Sunlight spans from ultraviolet through visible light and far into infrared. It contains a natural balance between shorter blue wavelengths and longer red wavelengths. That balance has been present throughout our evolutionary history.
Ultraviolet light is important, not least because it supports vitamin D production. But ultraviolet does not penetrate deeply, which is why too much of it causes surface effects such as sunburn.
Red and near-infrared light behave differently. At longer wavelengths, some light can pass through skin, bone, and soft tissue. Light above approximately 780 to 790 nm can even be measured emerging from the other side of the body in some circumstances.
That means longer wavelengths may reach tissues that ultraviolet and visible blue light cannot reach effectively, including the brain, lungs, liver, muscles, and potentially the heart.
How Deep Can Red Light Penetrate?
At 670 nm, light can penetrate through the skull and reach the cortex. It can also reach deep tissues, including the eye and potentially the heart through the relatively open spaces of the chest.
Longer wavelengths penetrate more deeply. Near-infrared light around 850 nm is invisible, but it can travel through the full depth of a hand and reach deeper structures than visible red light.
Bone is not the absolute barrier many people imagine. Long wavelengths can pass through it, although the signal becomes reduced. This is one reason transcranial applications of red and near-infrared light are so interesting for brain ageing and cognition.
There is also potential clinical relevance in ischaemia, where tissue has insufficient oxygen supply. Experimental evidence indicates that 670 nm light can improve ischaemic conditions. In principle, a low-risk intervention such as red light could be worth exploring in emergency settings, particularly if it offered even a modest benefit during an ischaemic crisis.
Red Light Dosage: More Is Not Necessarily Better
Dosing photobiomodulation is not as straightforward as simply increasing intensity or exposure time. Several variables matter:
- Wavelength
- Light intensity or irradiance
- Exposure duration
- Time of day
- The tissue and biological outcome being targeted
One of the more surprising findings is that the mitochondrial response behaves less like a standard dose-response curve and more like a switch.
In animal work, exposures below roughly one minute to one minute and fifteen seconds produced little effect. Once that threshold was reached, mitochondrial function improved, and the benefit could persist for around five days.
This does not mean that longer sessions are automatically better. Spending an hour in front of a red light device is unlikely to improve the effect and may make the treatment less efficient. There appears to be an optimal range, beyond which more exposure is not useful.
For studies of ageing and vision, a practical recommendation has been three minutes in the morning. Three minutes is probably more than the minimum required, but it is simple enough to build into a daily routine and avoids endless calculations over whether five days have passed since the last exposure.
Effective responses have been seen at irradiances around 5 milliwatts per square centimetre, which is relatively gentle. The experience should be comfortable, more like a dim bicycle light at a longer wavelength than a bright and unpleasant lamp.
Why Morning Exposure Matters
Timing is important. Red light appears to work much better in the morning than later in the day.
That makes biological sense. In the morning, blood glucose, hormones, ATP production, and alertness are changing rapidly as the body prepares for the day. This may be the point at which mitochondrial function is most responsive to being pushed upward.
By the afternoon or evening, the effect seems to be much smaller. If red light is being used specifically to support mitochondrial activity or glucose handling, morning is the sensible time to use it.
Reducing blue light in the evening can still be helpful for sleep in some people. These are different questions: bright blue light late at night may disrupt sleep, while red and near-infrared light in the morning may be more useful for mitochondrial stimulation.
Inflammation, ATP, and Reactive Oxygen Species
Mitochondria do much more than make ATP. When they are not functioning well, they can contribute to inflammation.
A useful analogy is a battery. A well-functioning battery delivers energy. A failing battery leaks. In mitochondrial terms, declining ATP production is often accompanied by increased reactive oxygen species, sometimes abbreviated as ROS.
As mitochondrial efficiency falls, ROS can rise, and inflammatory pathways may be driven upward. In ageing tissues such as the retina, this relationship is very clear. The eye uses enormous amounts of energy and is one of the tissues most vulnerable to mitochondrial decline.
When older animals are exposed to red light, ATP production can increase while ROS and a range of inflammatory markers decrease. Some markers fall more dramatically than others, but the overall relationship is consistent: healthier mitochondria are associated with less inflammatory stress.
The effect may be smaller in tissues with relatively few mitochondria, such as tendons. But in energy-hungry tissues such as muscle, retina, and nervous tissue, the potential for an effect is much greater.
What Animal Studies Suggest About Healthspan
Research in flies and bees has offered an important clue about how red light may influence ageing. The most striking effect was not a dramatic increase in maximum lifespan. Rather, it was an improvement in average life expectancy and healthspan.
In large populations of flies and bees, mortality typically rises in middle age. With bursts of red light, fewer animals died during that middle-aged period. By three quarters of the way through their normal lifespan, there were substantially more animals still alive.
They also performed better. Flies exposed to red light were better able to climb, which is unsurprising because muscle tissue is packed with mitochondria.
This matters because the aim of healthy ageing should not simply be to add time at the far end of life. It should be to reduce the number of people who become frail, immobile, and metabolically unwell in their fifties, sixties, and beyond.
Bee research has also had a practical application. Some pesticides damage mitochondria, and red light exposure has helped bees cope better with pesticide-related stress. Commercial beekeepers have begun using red light in hives, and there is interest in using it during long-distance transport of bee colonies, when stress can be substantial.
Red Light and Cognition: Why the Brain Is a Logical Target
The nervous system consumes vast amounts of energy to maintain membrane potentials. Neurons constantly pump ions across their membranes, and that process is heavily dependent on ATP.
As mitochondrial function declines with age, membrane potentials can become harder to maintain. That makes cognition an obvious area for investigation.
In experiments with older flies, memory declined in a very measurable way. Flies were trained to avoid quinine placed in a tube. Young flies remembered the unpleasant experience and avoided it the next day. Older flies repeatedly made the same mistake.
After short red light exposure over several days, the older flies remembered much better. They were more likely to avoid the quinine, and analyses of their brains showed higher ATP levels and healthier mitochondria.
The key point was not merely that a molecular marker changed. Behaviour changed too.
Other laboratories have reported encouraging findings in mouse models of dementia, but robust long-term human trials are still needed. The basic logic remains strong: if red and near-infrared light can reach the cortex and support mitochondrial function, cognition is a very reasonable target for serious investigation.
Early Human Research: Vision and Macular Degeneration
The retina is one of the most energy-demanding tissues in the body, which makes it particularly vulnerable to age-related mitochondrial decline.
Research using 670 nm light has shown improved visual function in older adults. A pilot study of 670 nm photobiomodulation examined healthy ageing and age-related macular degeneration, a condition with a strong mitochondrial component.
Age-related macular degeneration is a major cause of central vision loss. If people lived long enough, a very large proportion would develop it. Early intervention is likely to be crucial.
An initial trial in established disease did not produce the hoped-for result. Looking back, the reason was clear: the disease was already too advanced in many participants. Once central retinal degeneration is well established, it is much harder to reverse.
Later work focusing on people at earlier stages of disease, when early retinal deposits called drusen were present but degeneration was less advanced, produced much more positive results.
This is a broader lesson for mitochondrial disease. Whether the condition is macular degeneration, Parkinson’s disease, metabolic dysfunction, or another age-related problem, intervening before extensive tissue degeneration may offer the greatest opportunity.
Can Red Light Improve Blood Glucose Control?
One of the most striking human findings concerns blood glucose.
If red light improves mitochondrial activity, mitochondria should require more fuel. Their main rapid fuels are oxygen and carbohydrates, including glucose. That led to a straightforward question: could stimulating mitochondria reduce the rise in blood glucose after a glucose load?
In healthy participants, researchers used a standard glucose tolerance test. Participants consumed glucose, had their blood glucose monitored, and had oxygen consumption assessed. Some received a burst of red light to a relatively small area of the back before the glucose load.
The result was striking. The usual post-glucose blood sugar peak was significantly lower in the red-light group. The study was repeated because the initial effect was large enough to require careful confirmation, and the same result was found again.
A paper detailing this work, Light stimulation of mitochondria reduces blood glucose levels, describes the findings in more depth.
Why a Small Area of Light Could Have a Whole-Body Effect
It may seem odd that illuminating a small patch of the back could influence blood glucose throughout the body. But mitochondria do not operate as isolated units.
When mitochondria are perturbed in one region of the body, they appear to signal to mitochondria elsewhere. This may involve cytokines and other circulating signalling molecules. Animal studies have shown that red light exposure can alter cytokine profiles, and earlier work in simple organisms suggested that changing mitochondria in one location can produce effects throughout the organism.
That systemic signalling could explain why local red light exposure has wider metabolic effects.
Ongoing work in people with type 2 diabetes has so far shown similar patterns. The critical issue in diabetes is not merely that blood glucose rises. It is how high and how sharply it spikes. Those spikes are particularly difficult for blood vessels.
Population studies in the Netherlands and the United Kingdom have also found that people with type 2 diabetes who spend more time working outdoors tend to have lower glucose peaks than office workers. This does not prove that infrared light is the only reason, but it fits the larger biological picture.
Where Does the Extra ATP Go?
An important unanswered question is what happens to the ATP generated when mitochondrial activity increases.
Some ATP can be buffered through conversion to ADP, but the more likely explanation is that metabolism rises overall. The body may produce more ATP while also using more ATP.
ATP is difficult to measure continuously in living people, so this remains an active area of research. There are hints that some patterns of red light exposure may be associated with slightly higher body temperatures, which would fit with increased mitochondrial activity. Mitochondria themselves operate at temperatures above normal core body temperature and contribute substantially to body heat.
There are also early indications from athlete studies that red light exposure may influence body weight, although this was not the main aim of those experiments and should not be overstated.
The Problem With Modern Blue-Heavy Lighting
Blue light is not inherently bad. We need blue and ultraviolet wavelengths as part of a healthy light environment, and ultraviolet exposure supports vitamin D production.
The problem is imbalance.
Modern LED lighting is typically strong in blue wavelengths and contains very little red or near-infrared light. At the same time, much modern architectural glass blocks infrared light. People can spend all day indoors under blue-heavy LEDs while receiving little of the long-wavelength exposure that would have been normal in a natural outdoor environment.
Experimental work suggests that excessive blue light can run mitochondrial function down. In mice, substantial blue-light exposure has been associated with rapid weight gain and disrupted blood glucose regulation.
There are also concerns from the International Space Station, where astronauts spend extended periods in an artificial light environment. Some astronauts have become prediabetic during long missions. Their environment is dominated by harsh LEDs, while the station’s glass blocks infrared and generally faces Earth rather than the Sun.
LEDs have delivered enormous energy savings, but biology may have paid a price. The challenge is to develop lighting systems that preserve efficiency while restoring a healthier spectral balance.
Do Blue-Light-Blocking Glasses Solve the Problem?
Blue-light-blocking glasses may help some people sleep better when used later in the day. However, blocking blue light is not the same as restoring red and near-infrared light.
A healthy approach to light should be about balance, not declaring one colour good and another bad. We need blue light, particularly earlier in the day. We also need more exposure to the longer wavelengths that have largely disappeared from modern indoor environments.
Practical Ways to Get More Beneficial Light
The simplest advice is not expensive: go outside.
A walk in the park is particularly useful. On a warm day, leaves remain relatively cool because they reflect a great deal of infrared light. That means a green outdoor environment can be rich in reflected infrared wavelengths.
Clouds are not a reason to stay indoors. Infrared light passes through cloud cover far more effectively than many people assume, although it becomes more scattered.
- Walk outdoors daily: An hour outdoors supports light exposure, muscle activity, glucose use, and general health.
- Prioritize mornings: Morning light is likely to be more effective for mitochondrial stimulation than afternoon exposure.
- Think about indoor lighting: If practical, use warmer lighting and consider whether some incandescent-style lighting has a place in your environment.
- Build a simple routine: If using a red or near-infrared device, a short morning session while making coffee or listening to the news is more realistic than complicated scheduling.
- Do not overdo it: A few minutes is likely more useful than prolonged sessions.
- Move after eating: A walk after a large carbohydrate meal helps muscles use glucose and may reduce the size of the post-meal glucose rise.
Healthy ageing should not require vast spending. Returning, as much as possible, to the natural light environment under which we evolved is a sensible and affordable place to begin.
Safety, Limits, and Important Caution
Red and near-infrared light have generally been well tolerated in research involving older adults and children with mitochondrial disorders. Long-term participants exposed over many years have not shown obvious adverse effects.
However, one major area of caution remains: proliferative disease, including cancer.
Some naturally proliferating cells can grow somewhat faster under red light exposure. There is no direct evidence presented here that red light is harmful in cancer, but the possibility is serious enough that researchers have chosen not to use it in people with proliferative diseases.
That is the correct approach. Until the question has been properly answered, caution is warranted. Red light should not be treated as a replacement for medical care, especially for cancer, diabetes, neurodegenerative disease, or serious eye disease.
For a broader discussion of how photobiomodulation may influence ageing, see the review Does photobiomodulation influence ageing?.
Where Red Light Research Could Go Next
The most exciting future applications are not necessarily large, expensive machines. They may be simple, accessible systems built into ordinary life.
Imagine a device integrated into a cash machine or another everyday surface. A person places a hand down for identification, receives a short near-infrared exposure, and potentially gets a systemic mitochondrial stimulus without any inconvenience.
Because 850 nm light can pass deeply through the hand, that sort of intervention is theoretically possible. In the future, optical systems may even be able to identify people with poorer mitochondrial function and target interventions more precisely.
There is also interest in discreet lighting built into the walls of nursing homes. Near-infrared wavelengths around 850 nm are largely invisible, so they could potentially be incorporated into living spaces without disrupting vision or routine.
For brain applications, nasal light delivery is also worth investigating. It may sound unusual, but the nasal cavity offers a route through which light could potentially reach deeper cranial structures. The question is not whether one delivery method sounds strange. The question is which method delivers the right wavelength, to the right tissue, safely and cheaply.
The Most Meaningful Work: Mitochondrial Disease in Children
Perhaps the most compelling area of research involves children with severe mitochondrial disease. These children can be profoundly limited in mobility, and many face shortened lives.
Early results in a small clinical setting have been remarkable. Improvements were initially measured in eye function, but families reported wider changes too. Some children who had struggled with mobility were walking to school.
When light treatment was stopped, some drifted backward. When it was continued, the benefits were maintained. This is exactly the kind of result that makes the field worth pursuing with urgency and rigour.
There is still a vast amount to learn. We need long-term studies of cognition, balance, mobility, metabolic health, Parkinson’s disease, dementia, and the many other conditions in which mitochondrial decline is involved.
But the central message is already clear. Light is not merely for vision. The right wavelengths, delivered at the right time and dose, may be one of the simplest ways to support the energy systems that keep us functioning well as we age.
