There is a significant concern about the amount of short-wavelength light people, especially children, are exposed to from indoor lighting. Glen Jeffery states this is a major public health issue, comparing its potential danger to that of asbestos.

This is an issue on the same level as asbestos. This is a public health issue and it's big. And I think it's one of the reasons why I'm really happy to come here and talk, because it's time to talk.

When using LEDs in lab settings on the retinas of mice, it is possible to observe mitochondria gradually degrading. They become less responsive, their membrane potentials decrease, and they do not respire effectively. This process can be watched in real time.

The light we perceive with our eyes is only a small fraction of the total light emitted by the sun. Glen Jeffery explains that the visible spectrum for humans runs from deep blue-violet to deep red, roughly between 400 and 700 nanometers. However, the sun's output is much broader, extending into the invisible ranges of light.

On one end, there are shorter wavelengths that go down to about 300 nanometers. These are the deep blues and violets, including ultraviolet (UV) light. These short wavelengths are very high frequency and carry a significant amount of energy, which Glen describes as a "kick." This is why UV light is responsible for causing sunburn. On the other end of the spectrum, beyond what we can see, are the longer wavelengths that extend out to almost 3,000 nanometers into the infrared range. These wavelengths carry a different kind of energy but lack the potent kick of the shorter wavelengths.

We could separate those out by shining light through a prism. Think the cover of the Pink Floyd album. And that's separating out the different wavelengths.

The key point is that when you are in sunlight, you are exposed to all these colors and wavelengths, not just the ones you can see. While we are naturally aware of the visible light, the vast amount of invisible light also has biological effects.

Light is a form of radiation, but not all radiation is dangerous. Short wavelengths below UV are ionizing, meaning they can alter DNA with excessive exposure. The body has natural ways of blocking these wavelengths. Sunburn, for instance, is an inflammatory response that occurs because the skin blocks these wavelengths, preventing them from penetrating deeper. The energy gets concentrated on the skin's surface. Similarly, the eye's lens and cornea block these short wavelengths, which is partly why we don't see them. However, too much exposure can cause snow blindness, which is essentially a sunburn on the cornea and lens, or lead to cataracts over time.

A cataract is when the lens becomes more opaque and brownish with age. Glen Jeffery describes the remarkable effect of cataract surgery, which replaces the clouded lens with a clear one.

Take an older person, they've got this thick brownish lens, and pop it out and put a clear lens in. And the instant response in 90% of them is, wow. Suddenly they're getting a lot more light in their eye because the lens was brown, it blocked a lot of the blue wavelengths. And so they go, everything is very bright. Everything's very sparkly.

While the conventional wisdom is to protect our skin and eyes from UV light, some dermatologists are re-evaluating this advice. Glen points to the work of Richard Weller from Edinburgh, who has found that all-cause mortality is lower in people who get a lot of sunlight. Weller’s argument is that the primary goal should be to avoid sunburn, not necessarily sun exposure itself. This adds nuance to the discussion about skin cancer. Andrew Huberman adds that a dermatological oncologist he spoke with noted that the most deadly melanomas are often not associated with sun exposure and can appear on parts of the body that get very little sun.

The conventional wisdom linking sunlight to skin cancer may be incomplete. Glen points to the work of Richard Weller, who has challenged long-held assumptions in dermatology. Weller notes a paradox in the data: if sunlight were the direct cause of skin cancer, one would expect patients to have high levels of vitamin D. However, the opposite is often true.

In skin cancer patients, they've got relatively low levels of vitamin D. So that story needs to be unpacked. What's happened in the dermatological literature is that we followed an assumption and it's gone a very long way down the line.

Andrew agrees, acknowledging the common narrative that excessive sunlight leads to skin cancer. However, he points to compelling counter-evidence from a Swedish study showing reduced all-cause mortality in people who get significant sun exposure. Glen adds that a similar study from the University of East Anglia supports this finding with very large numbers. The reduction in mortality is not random; it is primarily linked to lower rates of cardiovascular disease and other cancers. Both agree that this is an important area for public health that requires further investigation, while still advising people to get sunlight without burning their skin.

The research on how long wavelengths of light affect mitochondrial function is rapidly expanding. A Russian scientist named Tina Karou was the first to propose this idea, suggesting that mitochondria absorb long waves of light. However, her work was largely ignored at the time.

Glen Jeffery describes his own attempts to verify this. When he tested mitochondria in a lab, he found they absorbed damaging blue light, but he could not find evidence that they absorbed red light. This led to a new hypothesis centered on what does absorb long-wavelength light: water. The sea appears blue precisely because water absorbs the longer, red wavelengths of the light spectrum.

The current theory is that long-wavelength light affects the viscous "nanowater" surrounding the tiny spinning motors inside mitochondria that produce ATP, our body's energy currency. By changing the water's viscosity, the light allows these motors to spin faster and generate more energy. This elegantly explains the effect without the mitochondria needing to absorb the light directly; instead, their environment is altered.

Glen explains this process using an analogy. The immediate effect is like a train running down a track faster. But a secondary, longer-term effect also occurs.

Giving red light gets the train to run down the track faster. That's true. But then something detects the speed of that train and says, lay down more tracks, we need more tracks.

This means the cell responds to the increased energy production by synthesizing more of the proteins that form these energy-making chains. So, long-wavelength light both improves the immediate function of mitochondria and influences their structure for enhanced long-term performance. This makes evolutionary sense, as mitochondria are thought to have originated as bacteria living in water, making them naturally responsive to light's effect on their aqueous environment.

The color of an object depends on which wavelengths of light it absorbs versus which it reflects. The ocean appears blue because it absorbs long-wavelength red light and reflects short-wavelength blue light. Conversely, a red apple appears red because it reflects long-wavelength red light back to our eyes. White objects reflect all wavelengths, while black objects absorb all of them.

This principle extends to the cellular level. It makes sense that mitochondria would absorb red light. The improvements in cellular function following exposure to longer wavelength light correlate tightly with the absorption spectrum of water. Glen Jeffery notes that this connection to water was overlooked for a long time because researchers can get stuck in specific lines of thinking.

Scientists make really big mistakes in the pathways that they follow. And they don't talk about their mistakes, but their mistakes are every bit as important as their great results. Why didn't we think about water? Because our minds were trapped in a certain pathway going down a certain alleyway.

Research has shown that long-wavelength light can penetrate deeply into the body, even through clothing, impacting mitochondria throughout its path.

Unlike UV light, which is blocked by the skin, long-wavelength light can penetrate deep into the body. When you stand in the sun, the vast majority of this long-wavelength light gets through your skin and is absorbed. Glen explains it has a very high scattering ratio, meaning it enters the body and bounces around internally.

An experiment illustrates this phenomenon. If you stand a person in sunlight and place a radiometer, which measures energy, and a spectrometer, which measures wavelength, on their back, you find that a few percent of the light comes out the other side. The crucial point is what happens to the rest of the light. Very little bounces back from the surface of the skin; instead, it is absorbed within the body. This means long-wavelength light penetrates our skin, bounces around our internal organs, and some of it even exits the other side.

Glen discusses the advantages and annoyances of working in silos with people from different fields, citing his work with Bob Fosbury, an astrophysicist from the European Space Agency. When Glen wanted to experimentally measure if light goes through the body, Bob initially dismissed it as obvious based on physics principles. Glen, however, believes in the importance of empirical demonstration.

I don't think you know something until it's published and everybody knows it and can talk about it.

Bob eventually became more interested and conducted his own experiments. He took different layers of clothing from his wardrobe and tested what light could pass through them. The results were surprising: long-wavelength light penetrates clothing, even up to six layers of a T-shirt. The color of the clothing, such as a black shirt, makes no difference. Standard fabrics are permeable, though something like rubber would block the light.

Another critical and not well-understood property of long-wavelength light is its tendency to bounce and scatter. When you shine a light source at a specific point, the light doesn't just stay there. It reflects around the room and even inside the body, making it difficult to control without using blocking materials like aluminum foil. This means that if you're using a light device in a confined space, the point source is the most concentrated area of energy, but you cannot assume it's the only source of that light reaching your body.

A study demonstrated that exposing a small portion of the skin to long-wavelength red light can alter the body's blood glucose response. This provides a controlled, scientific basis for anecdotal observations that eating outdoors might affect the body differently than eating indoors.

Glen Jeffery credits his colleague, Mike Powner, with the initial idea, which arose during a long car ride. Mike theorized that if red light makes mitochondria work harder, they will require more glucose and oxygen, thus pulling it from the blood. The idea was first tested on bumblebees. After being starved overnight, bees given red light before a glucose meal showed a smaller spike in blood glucose compared to those given blue light, which caused a very high spike. This suggested the mitochondria in the red light group were using more energy.

In the red light condition, their blood glucose does not go up as much. We give them blue light and their blood glucose goes very high. So they're using more of the energy.

The human experiment involved a standard blood glucose tolerance test, where fasted participants drank a sugary solution. When a burst of red light was administered beforehand, the results were unambiguous. The spike in blood glucose was reduced by over 20%. Glen notes that the spike itself, rather than the absolute level of blood glucose, is often the primary health concern.

Remarkably, the light was shone on a very small patch of skin on the participants' backs, yet it produced a systemic, body-wide effect. Glen explains this surprising result supports the growing understanding that mitochondria act as a community. They seem to communicate and coordinate their actions across the body. The duration of the experiment, about one to two hours, was long enough for this mitochondrial 'conversation' to take place.

We were stimulating a very limited area of the body, but we got a systemic response. There was no way that the mitochondria in that little patch of skin was having that effect. But it fits into a wider notion that all these mitochondria act as a community.

Research from John Mitrofanis in Australia has shown surprising results for red light therapy in primates. In his studies, he induced Parkinson's disease in primates using a drug and then applied red light to different parts of the body. Even when the light was shone on the abdomen, it significantly reduced the symptoms of Parkinson's, a disease that originates deep in the brain stem.

While this might seem strange, it fits within a broader spectrum of research. Glen suggests a potential mechanism for this effect. Long-wavelength light is known to reduce the magnitude of cell death, or apoptosis, in the body. This process is often initiated by mitochondria.

When mitochondria get fed up, and I see them as batteries, when the charge on the battery goes down low enough, they put their hand up and they say, time to die. And I think they actually present a molecular eat me signal.

Instead of just withering away, cells actively solicit their own death with this "eat me" signal, which triggers the immune system to clean them up. The red light applied to the abdomen may be working by offsetting the degeneration of dopamine neurons, which is characteristic of Parkinson's disease, by reducing this cell death process. The fact that these studies were conducted in primate models adds significant validity to the findings, as their biology is very similar to humans.

The eye's retina contains two types of photoreceptors. Cones handle color and bright light, while the more numerous rods are used for vision in low light, or dark adaptation. Examples include navigating to the restroom in the middle of the night or seeing the trail on a hike as dusk settles. Over a lifetime, a person will naturally lose about a third of their rod photoreceptors.

Glen describes an experiment showing that red light can slow this process. Aging mice were exposed to a daily burst of red light. When their photoreceptors were counted in old age, the results were clear. Glen explains, "We have reduced the pace of cell death in the retina. Red light is affecting mitochondria. Mitochondria have the ability to signal cell death, and we're drawing back the probability of that cell dying."

This finding aligns with other research showing red light can reduce cell death in the brain region associated with Parkinson's disease. This leads to a broader concept about mitochondria. In conditions like Parkinson's, dysfunctional mitochondria in one area may influence other parts of the body. This suggests mitochondria are not isolated units but an interconnected community that shares information, both good and bad, across different cells and tissues.

The big takeaway here, and it's not controversial to say, is that they're a community. You can't deal with them in isolation. Even across cells in different areas of the body. They're a community.

Andrew adds that some evidence suggests mitochondria might even be released from cells to communicate, similar to neurotransmitters. This communal nature harkens back to the theory that mitochondria were originally independent bacteria that formed a symbiotic relationship with our cells.

A common question is whether long-wavelength light can penetrate dense tissues like the skull. The answer is yes. Glen Jeffery explains that if you shine a long-wavelength light source through your hand, the light passes straight through the bone, making the bones invisible. What you do see are the veins, because the deoxygenated blood absorbs the red light. Andrew Huberman highlights a counterintuitive point: people often assume the light is affecting the structures they can see, like the veins. In reality, the significant finding is that the light is passing through everything else, including bone.

This means that when you are out on a sunny day or near a long-wavelength light source, that light is penetrating deep into your brain tissue through your skull. Glen had the same initial difficulty with this concept but confirms it is measurable. He cites the work of Ilyas Takhtanides, a biomedical engineer at UCL, who uses this principle for a remarkable medical application.

He passes red light wavelengths through the side of a neonate's head and records them coming out the other side. He can use that as a metric of how well the mitochondria are functioning in that damaged brain. And the readouts that he gets are indicative of the potential survival level of that neonate.

The reason this procedure is safe, even for babies, is because long-wavelength light is non-ionizing. Unlike UV or X-rays, it does not alter the DNA of cells. Instead, it contributes to the healthy function of mitochondria. This safety profile is well-understood by physicists on ethics committees, which is why such studies receive approval even for vulnerable populations.

The discussion shifts to retinal aging and the use of long-wavelength light. Andrew Huberman defines this spectrum as including red light around 650 nanometers and near-infrared (NIR) light out to about 900 nanometers, with infrared light existing beyond that. Glen Jeffery clarifies that most relevant research focuses on the range where vision typically stops, around 700 nm, and the near-infrared spectrum up to 900 nm.

Glen explains that human perception of light is not absolute. The limits of our vision can be extended by increasing the light's energy. He shares an anecdote from an experiment which confirmed that reindeer can see UV light. During this work, he noticed that he too could see the flashing UV light, which should have been outside his visible range. This principle applies to other wavelengths as well.

You will see wavelengths of light that you shouldn't see if you just turn the energy up. So if I put you in a room with UV and I pump loads of energy into that UV, you'll see things that you shouldn't. And likewise with the reds, you shouldn't really see much above 700. I can get you to see 750 if I just turn the energy up a bit and you see these little red glows.

The mitochondrial theory of aging posits that mitochondria regulate the pace of aging. Therefore, if you can regulate mitochondrial health, you can regulate aging. This is particularly relevant for the eyes. The retina has more mitochondria than any other part of the body, giving it the highest metabolic rate. Glen Jeffery compares it to a sports car that is driven hard and needs servicing, otherwise it falls apart. This high metabolic rate means the retina ages fast, making it a prime target for mitochondrial manipulation.

To test this, a study was conducted to measure people's ability to see colors. Using a high-resolution monitor, researchers presented letters, like a blue 'T' or a red 'F', against a noisy background to find the threshold at which a person could identify them. After establishing this baseline, subjects were given a burst of red light aimed at improving mitochondrial function in the retina. When they were retested, their visual threshold had improved. Almost every subject could see things they couldn't see before.

The size of the effect is around 20%. It's very substantial. But our ability to improve visual function varies enormously between individuals.

This 20% improvement in threshold indicates that people were seeing significantly better after the red light exposure.

In early experiments, a 670nm deep red light was used to test its effects on vision. This specific wavelength was chosen because a significant amount of previous research had used it, providing a reliable database. The initial protocol involved subjects looking at a small flashlight emitting this light for three minutes. This could be done with eyes open or closed, as the long-wavelength light easily passes through the eyelid.

Remarkably, just one three-minute session was enough to produce a significant improvement in color vision, observable as soon as an hour later. This positive effect was not permanent. Across multiple species, including flies, mice, and humans, the improvement consistently lasted for about five days. Glen notes that this suggests a fundamental mechanism that has been conserved throughout evolution.

The effect isn't based on a typical dose-response curve where more exposure yields better results. Instead, it acts more like a binary switch.

It's a switch. There's not a dose response curve here. You put enough energy in at a certain wavelength of light and it goes bang and click and then five days later goes chunk and stops.

Regarding the specific wavelength, Glen explains that light at 670nm and higher wavelengths works similarly well. However, as the wavelength decreases toward 650nm, the positive effects tend to be reduced.

A key question is whether natural sunlight can produce the same effects as a targeted long-wavelength light source, like a red light torch. Glen is a strong advocate for natural sunlight, noting that life has evolved under it for billions of years. He explains that sunlight provides an enormous broad spectrum of light, whereas a flashlight offers just a narrow window of specific wavelengths. For this reason, he considers the two situations to be incomparable.

While much can be achieved with single, long wavelengths of light, it can never fully replicate what is available from sunlight. However, controlled experiments are much easier to conduct with specific wavelengths than with the variability of natural sunlight. This is especially true in places like the UK where sunny days can be infrequent.

Even on heavily overcast days, a lot of photon energy still comes through. However, Glen clarifies that long-wavelength light is scattered and absorbed by water in the clouds. This means on a winter day, the longer wavelengths are slightly attenuated and come at you from many different angles, unlike on a sunny day when the light is more focused. Despite this, you still receive a lot of beneficial long-wavelength light. To ensure consistent daily exposure, Glen offers a simple solution.

Get a dog. Because you'll have to go out in daylight two or three times a day.

The effects of long-wavelength light on vision and mitochondrial function appear to be gated by age, with a statistically stronger effect in people over 40. This makes sense from a biological perspective. As we age, our mitochondrial function declines, so there is more room for improvement in older individuals. However, Glen notes that people age at different rates, and there is individual variability. This is a key challenge in human studies compared to animal models, where variables like diet and activity are tightly controlled.

A critical factor for the effectiveness of this light therapy is the time of day. The biggest effect is consistently observed in the morning, up until about 11 AM. Mitochondria are not static; their activity and protein concentrations shift dramatically over a 24-hour period. In the morning, the body is preparing for the day, and mitochondria produce more ATP, the cellular fuel, than at any other time. Glen explains that he can improve mitochondrial function in the morning, but not easily in the afternoon.

My interpretation is that in the afternoon, well, the standard lab joke is they're doing the ironing, they're doing other things that as organelles, they need to do. I was surprised to find that a mitochondria at 9 o'clock in the morning was not a mitochondria at 4 o'clock in the afternoon.

When it comes to the protocol, the intensity of the light doesn't need to be high. Early experiments used very bright light, around 40 milliwatts per centimeter squared. However, research has shown that much lower, more comfortable levels around 8 milliwatts are equally effective. In fact, a lab accident revealed that even a very dim red light, as low as 1 milliwatt per centimeter squared, can still be effective. This was discovered when a researcher used a flashlight with run-down batteries and still achieved a positive result.

To summarize the practical application, one can use dim to moderately bright long-wavelength red light. It is important that the light is comfortable to look at. The positive effects on vision can occur at any age. However, the improvements are typically more pronounced in people who have already experienced some age-related vision loss, which is a natural process for everyone.

A clinical trial using red light for macular degeneration, a common age-related vision loss, yielded an unexpected result. Glen explains that macular degeneration is when the center of the retina degenerates, noting, "The retina is a sports car. It burns out." The trial failed to improve vision in patients with the condition. However, the control group, who were the patients' husbands, showed enormous vision improvement, especially their ability to see in the dark.

The team realized the patients' disease had progressed too far for the treatment to be effective. This led to a crucial insight about red light therapy.

Red light can impact on aging, it can impact on disease, but it can't do it if that disease has really got its teeth into you. So where we need to get into situations and is early on in disease.

Glen cites another example with rheumatoid arthritis, where the treatment had zero effect on patients whose hands were already twisted. This underscores that early intervention is critical for success. The focus should be on improving efficacy, not just achieving a minor improvement.

The conversation also explored how red light's effects spread through the body. While shining light on a specific area, like a kneecap, produces a local effect within a couple of hours, systemic effects on distant parts like the hand can take 24 hours to appear. The body needs time for the "story to spread." The signals communicating these effects are a key area of research. One mechanism involves changes in cytokine expression. A low-level increase in inflammatory cytokines can be protective, essentially telling the body to "brace yourself, something's coming," and mobilizing the immune system. Another potential communication method involves microvesicles, which travel through the body carrying different 'cargoes' and seem to change in concentration after red light exposure. Glen emphasizes the system's complexity, noting that to understand the complex changes across hundreds of cytokines, he'd need a mathematician. The conversation concludes by highlighting the incredible nature of mitochondria, including how healthy cells can donate mitochondria to sick cells to help them recover.

A good way to understand how water absorbs red light is through the experience of snorkeling on a tropical reef. In the first 10 feet of water from the surface down, you can see beautiful oranges and reds. As you go deeper, those colors seem to disappear. They haven't actually vanished; it's just that the red light from the sun doesn't penetrate that far into the water because it gets absorbed. If you bring a flashlight with you, as divers sometimes do, you can see those red fish are still there at deeper levels, their color revealed by the artificial light.

A serious concern exists regarding exposure to short-wavelength light from artificial sources. The common term 'blue light' doesn't fully capture the issue, as it's not just about light that appears blue. The problem lies with the white light from modern LED sources, which are now the standard for lighting.

The white light coming from LED sources... yes, they contain blue light, but they also contain violet light... In other words, white light coming from LEDs is very short wavelength enriched.

This is a potential problem if short-wavelength light causes mitochondrial dysfunction, which appears to be the case unless it is balanced by longer wavelengths. To understand how we arrived at this situation, it's useful to examine the evolution of lighting technology over the last few decades, moving from firelight and candlelight to incandescent and halogen bulbs, and now to the dominant LED bulbs.

A group of scientists is raising concerns that modern LED lighting could be a significant public health issue, with some suggesting it might be on the same level as asbestos. Glen Jeffery feels it's time to talk about the data. LEDs were celebrated for their energy efficiency because they concentrate their output on light we can see, unlike older incandescent bulbs. However, this efficiency comes at a cost. The light spectrum is fundamentally different from what humans evolved with over billions of years of sunlight, and more recently, fire and candles, which are all broad-spectrum.

The shift away from incandescent lights, which contained a lot of infrared, began around the early 2000s. The problem with LEDs, even warm ones, is that they have a large spike of blue light and a complete absence of red light. This unbalanced spectrum has demonstrable negative effects. In lab studies using mice retinas, mitochondrial function declines under LED lighting at levels found in typical homes. Flies exposed to blue light have shorter lifespans, and their mitochondria decline markedly.

Studies on mice reveal even more concerning systemic effects. Under LED lighting, mice gain weight because their mitochondria fail to process glucose effectively, which is then stored as fat. Their blood glucose regulation becomes unbalanced. Behaviorally, they show less confidence, which may indicate low-level chronic infection. Physiologically, they develop fatty livers, and their livers, kidneys, and hearts become smaller. They also exhibit abnormal sperm and testicular morphology. Glen clarifies it is the combination of a specific range of blue light (420-440nm) that mitochondria absorb and the absence of red light to counterbalance it that causes these issues.

This exposure to excessive amounts of short wavelength light because of LEDs is possibly as serious as asbestos exposure in terms of its detrimental effects to human biology.

This concern extends to human lifespan trends. While life expectancy in Western Europe has been steadily increasing, the curve began to flatten around 2010. Glen and his colleagues suggest that while not definitive proof, the widespread adoption of LEDs should be considered as a potential contributing factor to this trend, especially since broad-spectrum sunlight exposure is linked to longer life and lower all-cause mortality.

The potential harm from short-wavelength light may not be due to the light itself, but rather the absence of balancing long-wavelength light. Mitochondria evolved under a full spectrum of sunlight, including short, medium, and long wavelengths. Modern LED lighting disrupts this natural balance by heavily favoring short wavelengths and omitting the longer ones. This is like tipping a seesaw too far in one direction.

Andrew compares this to macronutrients. Just as most people thrive on a balance of proteins, fats, and carbohydrates, mitochondria thrive on a balance of light wavelengths. Demonizing one type of light is less accurate than understanding that the ratio is what's critical for biological function. LEDs are problematic because they so heavily weigh one side of this light mechanism.

Glen cautions against trusting commercial labels on LED bulbs, such as "sun-like" or "full spectrum." He has never found a commercial LED that provides significant light beyond 700 nanometers. Creating a truly full-spectrum LED would require a vast and expensive array of individual lights, which isn't commercially viable. Furthermore, research shows that mitochondria can distinguish between different types of light sources. They do not respond as positively to a compressed series of LEDs as they do to the smooth, continuous spectrum of an incandescent bulb or natural sunlight.

Isn't it amazing that mitochondria can sort that one out? I think it's really cool. There's a load more there that I think we're going to find out. They're doing things that are just inconceivable at the moment.

The light spectrum from an incandescent bulb is highly similar to that of the sun. It provides a smooth, continuous function, gently drifting from short to medium to long wavelengths. This is the kind of light humans evolved with. As people migrated from Africa into darker northern regions, they used fire as a light source.

They had a light source that was very solar like. And so there was no issue there.

This continuity was broken by a dramatic change in the early 2000s with the introduction of modern lighting. For the first time, human bodies were exposed to a radically different type of light.

Your body has never experienced such confined limited spectrum of life, never experienced it before.

A strong warning is issued against the use of lasers on the body. Glen explains that monochromatic light from lasers is completely new to life on Earth. Andrew reinforces this by urging people not to shine lasers in their face, eyes, or on their skin, stating that only trained medical professionals should handle them for specific procedures.

Please folks, do not shine lasers in your face. No eyes. Do not, in fact don't shine lasers on your skin. The only people who should be shining lasers on bodies are trained medical professionals.

The conversation then shifts to other artificial long-wavelength light devices, such as those for red and near-infrared light therapy. When asked if these can offset the negative effects of LED lighting, Glen suggests that while most probably do no harm and may have a positive impact, there is a significant issue with their quality. Many of these devices are poorly made, with low-quality components and inconsistent energy output.

An LED is like buying a car. You can buy a bad car or you can buy a very good car. A lot of the LEDs are not what they say they are.

Glen notes that specific, popular wavelengths like 670nm are hard to source, so many products don't actually deliver what they claim. Furthermore, their performance can degrade significantly over time. Andrew agrees, comparing the situation to the broader health and wellness industry, where there is a wide range of quality from medical-grade equipment to unreliable consumer products.

Incandescent bulbs are no longer widely available in North America, but halogen bulbs, which are nearly identical, can still be found. The importance of these types of lights was highlighted in a study Glen conducted at University College London. The study took place in windowless buildings with harsh LED lighting. Staff members were given 40-watt incandescent desk lamps to supplement their environment.

After two weeks, their color perception for both blue and red improved significantly. This effect was much greater than improvements seen with long-wavelength red LEDs. Surprisingly, the improvement was maintained for over a month after the incandescent bulbs were removed. This led Glen to wonder if the modern built environment is suppressing our physiology through its impact on mitochondria. He questions whether his past experimental results were so dramatic simply because his subjects were drawn from a population already living under suppressive LED lights.

If I went and did those same experiments on a group of farm assistants, or people who are doing surveying of the countryside, would I get the same effect? I think that in the built environment we are suffering from a suppression of our physiology.

A major issue in modern architecture contributes to this problem. When building projects go over budget, costs are often cut on lighting, which is one of the last elements to be installed. This results in the use of the cheapest LEDs with the most restricted light spectrums. Compounding this, commercial buildings often use infrared-blocking glass to regulate temperature. This creates a "double hit": the poor quality of the LED lights combined with being isolated from the full spectrum of natural light. For people who spend most of their time indoors, getting outside is crucial. Supplementing the indoor environment with a halogen or incandescent lamp can also be beneficial, especially during winter.

Andrew expresses concern about modern light environments, particularly for children who spend a lot of time on screens and indoors. He notes that while some people are highly sensitive to light's impact on sleep, the blood glucose-elevating effects of short-wavelength light at night seem more universal. He cites a study from the Proceedings of the National Academy of Sciences where sleeping under even a dim 100-lux light raised morning blood glucose levels, likely due to a cortisol increase.

Given these concerns, Andrew questions whether people in LED-rich environments need to supplement with long-wavelength light. However, Glen offers a surprising counterpoint based on his own research.

So myself and a load of my colleagues have sat with a blue screen staring at it all day for days. Mind bogglingly boring thing to do. It had almost no effect.

Glen explains that this is because the type of blue light emitted by most screens is not in the most damaging range. He clarifies the distinction in wavelengths.

The blue in most of those screens is actually rather long wavelength blue. So it's blue pushing 450 plus. So it's not in that danger zone, which is, which I regard as 420 to 440.

Because of this, Glen is not as worried about the negative effects of screen light as he once was.

Pediatric ophthalmologists are concerned about the rise of myopia in children, particularly in Asia. This condition is linked to extensive close work, like staring at screens or books within a foot or two. Glen Jeffery explains that an absence of long-wavelength light is a key driver of this problem. Myopia is more than just needing glasses. The condition causes the eye to grow too long, which stretches the retina. By the time that child reaches 40 or 50, this stretched retina, combined with natural age-related cell loss, can lead to tears and a form of macular degeneration.

In China, authorities have taken steps like installing bars on school desks to force children to sit farther from their work. They have also tried using red light therapy, but unfortunately used lasers. Glen strongly warns against this approach. Unlike LED light which scatters uniformly, laser light creates intense hot spots called caustics, which can burn out parts of the retina. He believes lasers are often used simply because they sound more powerful.

Never ever use a laser unless there is a profound medical reason for doing it.

Glen considers myopia a "ticking time bomb." He suggests simple, effective solutions. Schools should have untinted windows. They could also use incandescent lights, which produce ample infrared light even when on a dimmer switch because they generate heat. Another powerful tool is incorporating plants into the environment. All plant matter reflects infrared light, which is why a leaf in direct sun does not feel hot. Planting trees outside and having plants indoors can reflect beneficial infrared light into our living spaces. Glen mentions a study where a city planted a thousand trees and later found a significant reduction in blood markers for stress and systemic inflammation among residents.

Our modern indoor environments, filled with concrete, LED lights, and infrared-blocking windows, are depriving us of essential light. Glen Jeffery raises a key question about the physiological effects of this deprivation: what happens to our blood when we move from a concrete building into a park? The feeling of well-being we experience outdoors suggests a significant biological shift is occurring. As our species becomes more modern, we increasingly live, work, and even exercise indoors, making it crucial to bring the critical elements of the outside world, specifically long-wavelength light, back into our indoor spaces.

Andrew Huberman shares his personal experience of using a long-wavelength light device in the morning, noting a tangible increase in energy and well-being. This aligns with the growing concern that the current lighting situation is a major public health problem. An excess of short-wavelength light from LEDs, combined with a lack of protective long-wavelength light, could lead to more metabolic dysfunction, visual problems like myopia, and accelerated neurodegeneration.

We think this is a significant public health problem.

The solution doesn't have to be expensive. While architects initially balk at the cost of changing lighting systems, they are starting to consider the larger economic model, including reduced sick days and faster patient recovery. For individuals on a budget, simple changes can make a difference. Andrew suggests using an odorless beeswax candle or, even better, an incandescent or halogen bulb to supplement long-wavelength light, especially in the evening.

Glen agrees, stating that these changes can be implemented at almost zero cost. He personally uses a halogen lamp in his kitchen in the morning. A key insight is that dimming a halogen bulb not only saves energy but also increases the proportion of infrared light it emits and makes the bulb last significantly longer. This simple strategy can be applied in various settings, from homes to critical care units and nursing homes, where vulnerable populations are often deprived of natural light. The heat from these bulbs, once seen as a waste product, can even be repurposed for warming a room.

It is important for everyone to think about their indoor lighting environment. This includes considering how much sunlight exposure and short-wavelength LED exposure they are getting during the day. This isn't about extreme biohacking, but about compensating for what we miss from being outdoors. Our mitochondria need long-wavelength light to be healthy, a point which Andrew credits Glen's work for demonstrating. Using incandescent bulbs, halogen lights, or even candlelight can make a meaningful difference in providing this necessary light.

Glen Jeffery shares a powerful story about the potential of red light therapy for children with mitochondrial diseases. In these conditions, the genetic code for producing ATP (the body's energy currency) is disrupted, leading to severe health issues and sometimes a lifespan of less than 25 years. He began receiving emails from parents of children with these diseases after his research on red light became known.

Though he lacked ethical approval to formally treat them, he offered suggestions. The first child who underwent the therapy experienced what Glen described as a "gut-wrenching" positive improvement. A key metric was ptosis, the inability to open one's eyelids. The child's condition improved so much that they regained semi-mobility. Glen recalls receiving a video of the child walking to school and being moved to tears by the impact.

I went to the bathroom and sobbed. Done something that really helps someone.

This led to a clinical trial, but it faced a significant hurdle: there were not enough children with mitochondrial disease in the UK to participate, and the funding ultimately had to be returned. Glen notes that theoretically, red light should help these children and, importantly, does no harm. He now suggests that people consider a simple intervention like changing the light bulbs in their homes to get more red light exposure.

He is also involved in an upcoming trial for retinitis pigmentosa, a common retinal disease, which will also explore changing light bulbs for patients. Despite these promising developments, he expresses frustration that new constructions, like the new Moorfields Eye Hospital, are being built with glass that blocks infrared light and equipped with poor-quality LED lighting, showing that there is still a long way to go in applying these learnings.