Thread by @sam_soete

A Guide on Near-Infrared Light

This 🧵covers the details of our natural light environment and the optics that the human body has evolved to take advantage of it.

Light is life... let me show you how.

The sun represents the single largest energy input to the human body with a solar spectrum extends between 250-4000nm.

Near-infrared (NIR) light has wavelengths that range from approximately 800nm to about 2500 nm.

70% of the photons emitted from the sun fall in the NIR range.

Think about that for a second....

The human body has evolved over millennia under a near-infrared (NIR) emitter, the Sun.

In nature, the human body is never exposed to potentially damaging UV or blue light without an excess of accompanying protective NIR photons.

As the day unfolds, the balance between near-infrared (NIR) and visible light changes.

At the break of dawn, the NIR-to-visible light ratios rise up to 3-to-1.

At the zenith of noon, equilibrium reigns with a harmonious 1-to-1 ratio.

As the sun sets towards the horizon, the scales tip once more, returning to a 3-to-1 NIR-to-visible light ratio.

At first, human ingenuity mimicked the celestial choreography of the sun.

Campfires and incandescent bulbs, embody a remarkable 10-to-1 NIR-to-visible light ratio.

For 600,000 years, we have gathered around the campfire, a source of NIR light, like moths to a flame.

However in modern society, 93% of our time is spent indoors where there is zero NIR exposure, representing the largest alteration to solar exposure in evolutionary history.

Simultaneously, our light environment is polluted by artificial light at night not found in nature.

LED & fluorescent lighting are "visible only" sources and emit no NIR photons.

Sunlight, fire, moonlight and incandescent light bulbs are NIR emitters.

There is no comparison between modern lighting environments and what we are exposed to in nature.

This radical shift in our light environment correlates with countless diseases including the myopia epidemic, sleep disruption, cancer, metabolic dysfunction, cognitive decline and autoimmune diseases.

Interestingly, natural entities such as grass, clouds and dirt absorb visible photons such as blue light but strongly reflect NIR photons.

In contrast, the body effectively filters UV and reduces high energy visual (HEV) photons such as blue light in sensitive tissues such as the retina, but concentrates and collects NIR photons.

The human body has evolved incredible optical mechanisms to harness and direct NIR photons towards specific areas such as the brain, retina, blood vessels and the skin.

Due to the low optical absorption of NIR in the body, NIR photons can penetrate several inches (>8cm) into the body (including the skull) and effect over 60% of the body's cells.

You can explore this at home by putting your thumb over the flashlight on your phone in a darkened room.

The blue and green photons are strongly absorbed while the red photons are emitted and uniformly distributed throughout the thumb.

Interestingly, most light clothing transmits NIR, allowing for significant exposure even when not at a nude beach.

Contrary to our intuition, the majority of photons impacting the retina don't enter through the pupil.

Instead the eyelid, sclera, and choroid transmit NIR to an incredible degree.

Furthermore, the scattering effect created by the low absorption of NIR of the skin and surrounding tissues compared to the high NIR absorption of haemoglobin in blood localizes NIR photons in the blood vessels.

I wonder why?

While the skull blocks UV photons, it effectively transmits NIR photons.

The cerebral spinal fluid (CSF) surrounding the brain also has its minimum optical absorption spectrum in the NIR range allowing it to permeate through the fluid and scatter on surrounding surfaces.

The brain's optics are designed in such a way as to distribute NIR photons to the grey matter, including even the deepest recesses of the brain.

It is no coincidence that the grey matter is located on the outside surface of the brain, and that the blood supply to the brain organizes itself starting from the outside and moving inward.

Neuromelanin in the grey matter has a very strong capacity to absorb NIR compared to the underlying white mater.

The brain is uniquely vulnerable to oxidative damage due to its weak antioxidant defences.

The NIR stimulates subcellular melatonin production in the mitochondria which acts as a potent antioxidant.

Similarly to CSF, amniotic fluid has a peak transmission in the NIR.

Light-guiding via the amniotic fluid bathes the fetus in NIR photons during early pregnancy when exposed to natural sunlight.

As the pregnancy progresses, the skin stretches allowing shorter wavelength photons to reach the fetus. NIR photons reduce MCP-1 proteins in amniotic fluid which are associated with autism.

Sunlight has also been shown to reduce blood pressure. Indeed, our blood pressure is lower during the summer months.

This is because NIR light stimulates nitric oxide (NO) production which dilates blood vessels. Blood flow as well as waste removal is increased.

Due to the deep penetration of NIR, most capillary networks are effected. This has incredible downstream effects on our risk of cardiovascular and kidney disease.

NIR also impacts our mitochondria in a fascinating way.

Complex IV in the electron transport chain, or cytochrome C oxidase, accepts NIR photons and releases NO into the mitochondrial matrix.

At higher concentrations, NO can inhibit mitochondrial respiration, particularly at complex IV leading to a reduction in ATP production.

The liberation of NO therefore enhances mitochondrial energy metabolism. NO also serves as a signalling molecule to promote mitochondrial melatonin synthesis.

I'll make sure to make another thread on why this mitochondrial melatonin production stimulated by NIR is so important.

If you want to support my work and are interested in a red-light device, check out EMR-TEK.

emr-tek.com/discount/SAMUE…

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