Light your cells can absorb.

The idea

Red light therapy, in one paragraph.

Red light therapy is the use of specific red and near-infrared wavelengths, at modest intensity, to change what cells do. The scientific name is photobiomodulation, or PBM: "photo" for light, "bio" for living tissue, "modulation" for a change in activity. Older papers call it low-level laser (or light) therapy, LLLT. ^{1 2}

The key word is modest. This is not a laser that cuts, a heat lamp that warms, or ultraviolet light that tans. It is light delivered at levels low enough that the effect researchers study is chemical and biological, not thermal. ^{1 14}

The idea in three steps:

Every other section on this page unpacks one of those three steps.

Light

Colour is a wavelength. Wavelength decides where light goes.

Light is energy travelling as a wave. The distance from one peak of the wave to the next is its wavelength, measured in nanometres (nm), billionths of a metre. Your eyes read wavelength as colour: violet sits near 400nm, green near 530nm, red runs out to about 700nm. Past that, light carries on but your eyes stop detecting it. That invisible band is near-infrared.

Wavelength does far more than set colour. It decides what happens when light meets the body: how much bounces off the surface, which molecules soak it up, and how far it travels before it is spent.

The three big absorbers in your tissue

Between those three there is a gap, roughly 600 to 900nm, where tissue absorbs the least and light travels the furthest. Physicists call it the optical window. It is the reason this whole field works in red and near-infrared, and the reason every Lumi wavelength sits in it or just beyond it. ^{1 10}

Absorption and scattering, the two things that happen to light in skin

Light inside tissue has two fates.

Absorption: a molecule tuned to that wavelength takes in the light's energy. That is the useful event, when the molecule is the right one. When melanin, haemoglobin or water take it instead, that light is no longer available for anything deeper.

Scattering: the light hits cell membranes, collagen fibres and other tiny structures and changes direction, again and again. Scattering does not destroy the light, but it spreads it sideways and sends some back out of the skin. Shorter wavelengths scatter more; longer ones scatter less. ¹

Each absorption and each scattering event takes a little light out of the forward beam, so the amount left falls steadily with depth. There is no hard stop. Penetration is a fade, not a wall.

Depth

How far the light goes, and what it meets.

Skin is layered, and each layer holds different cells.

Red light (630 and 660nm) is absorbed and scattered more, so most of it is spent in the epidermis and dermis: the layer where fibroblasts live. That is why red is the wavelength of skin research.

Near-infrared (810 to 850nm) is absorbed less by melanin, haemoglobin and water, and scatters less, so a larger share passes through the skin and carries on into fat, connective tissue and muscle.

What the measurements show

• A 2017 computer-modelling study of light travelling through a multi-layered model of human skin found that penetration depth increased as wavelength increased, with a deepest calculated value of about 5.4 mm. It also showed that skin tone and the width of the beam change how light is distributed. A 10 mm beam delivered 73 to 88% of the light that an infinitely wide beam delivered at depths of 1 to 3 mm. ¹⁰ A panel lighting a large area behaves much more like the wide beam than a narrow spot does.
• A 2015 study measured light passing through eight intact human cadaver heads. A broad 808nm beam travelled through scalp, skull and the brain's protective membranes into brain tissue to a depth of about 40 mm. Inside brain tissue, 808nm was absorbed and scattered less than both 660nm and 940nm. ¹¹

Reading those two numbers properly

They measure different things. The 5.4 mm figure is a modelled depth in skin where most of the light has been used up. The 40 mm figure is how far any measurable light reached. The same cadaver study also reported how quickly the light faded: for that system, the light fell to about a third of its level for roughly every 4.5 mm it travelled. ¹¹ So even the deepest-travelling light does most of its work in the first centimetre or so, and only a small fraction goes further.

The practical point: how much light arrives at any depth depends on how much arrives at the surface. That is why intensity and distance matter, covered under Dose.

Wavelengths

Every Lumi wavelength, explained.

The molecule at the centre of this field, cytochrome c oxidase, does not respond to all red and near-infrared light equally. In a 2005 analysis, researchers fitted seven action spectra (graphs of how strongly cells respond at each wavelength) from human cells lit with 580 to 860nm light and found four active bands: a red band peaking between about 613 and 624nm, a far-red band between about 668 and 684nm, and two near-infrared bands at about 751 to 772nm and 813 to 846nm. ⁶ Lumi Core's five wavelengths sit on or beside those bands. Pro adds two longer wavelengths that reach cells by different routes.

Tap a wavelength to open it.

"Travels" compares the wavelengths with each other. Exact depths depend on skin tone, body site and how much light arrives at the surface. ¹⁰

The cell

What happens in the first seconds.

This is the part most brands skip. It is also the part that explains everything else: why wavelength matters, why dose matters, and why more is not always better.

red / near-infrared light

1. 1 absorbed by cytochrome c oxidase in the mitochondria
2. 2 nitric oxide is knocked off the enzyme
3. 3 electron transport speeds up, more ATP (cell energy)
4. 4 a brief burst of reactive oxygen species (a signal, not damage)
5. 5 also: light- and heat-gated ion channels let calcium in
6. 6 messengers (ROS, cyclic AMP, nitric oxide, calcium) switch on transcription factors
7. 7 genes change: proteins for repair, movement, growth, antioxidant defence and lower inflammatory signalling

The power station

Almost every cell in the body contains mitochondria, small structures that use oxygen and nutrients to make adenosine triphosphate, or ATP. ATP is the energy currency cells spend on everything: building proteins, repairing damage, dividing, contracting and signalling.

The light-sensitive enzyme

ATP is made at the end of a chain of proteins in the mitochondria called the electron transport chain. One of the last links is cytochrome c oxidase (complex IV of the chain). It contains copper and haem centres, and those centres absorb red and near-infrared light. Its absorption bands line up with the wavelengths that produce effects in the lab, which is why researchers describe it as the primary photoacceptor in this field. ^{2 5 6}

Releasing the brake

Nitric oxide, a small signalling molecule, can bind to cytochrome c oxidase and get in the way of oxygen, slowing the whole chain. The leading hypothesis is that red and near-infrared photons knock that nitric oxide off the enzyme. Electron transport speeds up, the electrical charge across the mitochondrial membrane rises, and ATP production increases. ^{2 4}

A brief signal

When mitochondria speed up, they release a short burst of reactive oxygen species, or ROS. In large amounts, ROS damage cells. In small, brief pulses, they are messengers. Reviews of the field list a rise in ATP, a brief burst of ROS, an increase in nitric oxide and a change in calcium levels as the secondary effects of light absorption. ³

The same signal behaves differently depending on the state of the cell. In normal cells, light produces a small rise in ROS and can switch on NF-κB, a master switch for genes involved in cell survival. In cells already under oxidative stress, light has been reported to lower ROS and lift the cell's own antioxidant defences. In activated inflammatory cells, inflammatory markers fell. ^{3 4} Researchers describe this as one signal with apparently opposite effects, depending on the state of the cell.

The second pathway

Mitochondria are not the only target. Light-sensitive and heat-gated ion channels in the cell membrane can open when light is absorbed, letting calcium into the cell. Reviews suggest some of these channels may respond through light-absorbing proteins called opsins. ^{2 3} This route appears to dominate at longer wavelengths near 980nm, where water is the absorber. ¹²

From signal to genes

After the first absorption step, the message is passed along by ROS, cyclic AMP, nitric oxide and calcium. Transcription factors switch on, and the cell changes which genes it reads. The genes involved relate to protein synthesis, cell migration and multiplication, anti-inflammatory signalling, proteins that resist cell death, and antioxidant enzymes. Stem cells and progenitor cells appear especially responsive. ²

The sequence in one line: light is absorbed, the brake comes off, energy rises, a brief signal fires, and the cell changes what it makes next.

Cell to tissue

What that looks like in skin, blood and muscle.

Fibroblasts and collagen

Fibroblasts are the cells in the dermis that spin collagen and elastin, the proteins that give skin its firmness and spring. They sit in the zone where red light is absorbed. Reviews of light in skin describe a chain in skin cells: absorption by mitochondrial chromophores, then electron transport, ATP, nitric oxide release, blood flow, ROS and a range of signalling pathways, with stem cells involved in repair also activated. ^{15 16}

What researchers saw under the microscope: in a 2007 randomised, sham-controlled trial, skin samples taken after a course of 633nm, 830nm or combined LED light showed a marked increase in collagen and elastic fibres, and electron microscopy showed highly activated fibroblasts surrounded by abundant fibres. ¹⁷ In a 2014 controlled trial of 136 volunteers, collagen density measured by ultrasound improved in the light groups compared with controls. ¹⁹

Blood flow and oxygen

Nitric oxide is also the body's own signal for widening blood vessels, so its release is one proposed link between light and local blood flow. ^{2 15} In a 2017 human study of 1064nm light on the forehead, oxygenated and total haemoglobin rose in the tissue beneath during and after the light, compared with placebo. ¹³ More oxygen arriving is what busier mitochondria need.

Inflammatory signalling

Reviews describe an overall reduction in inflammation as one of the most reproducible effects of photobiomodulation, and single out joints and traumatic injuries as areas where it matters. Reported changes include lower inflammatory markers in activated immune cells and lower markers of the pro-inflammatory M1 type of macrophage, the immune cells that clear damage. ³ In the 2007 skin trial, levels of the inflammatory messenger IL-6 fell in skin samples after the LED course. ¹⁷

Muscle

Muscle is packed with mitochondria, which makes it one of the most light-responsive tissues studied. A 2016 review of 46 studies with 1,045 participants, from untrained volunteers to elite athletes, reported that light could increase muscle mass gained after training and decrease inflammation and oxidative stress in muscle biopsies. ³⁴ A 2018 review notes that light can act as a preconditioning step and can interact with exercise in muscle. ⁴

Together

Why a panel runs more than one wavelength.

A single wavelength only covers the depth it reaches and the pathway it drives. Combining them is a coverage decision, and there are three reasons for it.

1. Depth. Red is spent in the skin, where fibroblasts make collagen. Near-infrared carries past it into muscle and connective tissue. Running both means the same session reaches the surface and the tissue beneath it. ^{10 11}
2. More than one absorption band. Cytochrome c oxidase has four active bands between 600 and 860nm, and their exact peaks vary from one measurement to the next. ⁶ Five wavelengths spread across 630 to 850nm put light on or beside each band rather than betting on one.
3. More than one pathway. 810nm acts mainly through mitochondria; 980nm acts mainly through heat-gated ion channels. ¹² Pro's 960 and 1060nm add longer wavelengths that reach cells by a different route and to a different depth.

### most light. ## some. # little. . trace

What the trials combined: many of the studies on this page used more than one wavelength. The 2007 skin trial tested 633nm alone, 830nm alone and both together, and all three groups showed changes compared with baseline. ¹⁷ A 2005 facial study combined 633 and 830nm, a 2009 leg ulcer trial combined 660 and 890nm, and a 2015 volleyball trial combined 630 and 850nm. ^{18 25 35}

The honest note: combining wavelengths is a logic of coverage, not proof that more wavelengths add up to more effect. A 2014 trial of 136 people found that a broad 570 to 850nm spectrum showed no advantage over red alone for the skin measures it tracked. ¹⁹ That is why Lumi does not sell a longer wavelength list for its own sake.

How Lumi runs them:

The research

What researchers have studied.

Below is what researchers measured when they put people under red and near-infrared light, topic by topic, with how the light is thought to act in that tissue. Each line describes what happened to the participants in that study. Devices, wavelengths and doses differ from study to study and from Lumi panels, many studies used lasers rather than LEDs, and individual results vary. Read The limits next; it matters.

The limits

What the research does not tell you.

Authority means being clear about the gaps as well as the findings.

• Many trials are small. Several of the skin, acne and psoriasis studies above enrolled between 9 and 76 people. Meta-analyses pool more, but they can only be as good as the trials inside them, and some reviewers rate those trials low to moderate in quality. ³⁸
• Much of it used lasers, not LED panels. Much of the foundational and joint research used lasers applied to specific points. Laser and LED light differ, and reviewers caution against assuming results transfer automatically. ¹⁴
• Parameters vary enormously. Wavelength, intensity, dose, timing and frequency differ from study to study, and the field has no agreed protocol. That complexity is one reason the literature contains negative studies as well as positive ones. ^{7 9}
• Some trials were not blinded or had no sham or control group. Those are flagged above.
• Some areas are early. Sleep research and brain research in people are thin or preliminary.
• Laboratory cell studies explain mechanism. They do not show what happens in a whole person.
• A study result describes the people in that study. It is not a forecast of yours.

What is solid: the physics of the optical window, the identification of cytochrome c oxidase as a key photoacceptor, the biphasic dose response, and a body of randomised, placebo-controlled trials across skin, hair, joints and muscle that is larger than most people realise. ^{1 2 7 30 34}

Lumi products are not therapeutic goods and are not intended to diagnose, treat, cure or prevent any disease or medical condition. Information here is general and is not medical advice. If you're pregnant, have a medical condition, or take medication that makes you sensitive to light, check with your doctor before use.

A session

A session, built on the science.

Everything above comes down to a few habits.

1. Bare skin. Clothing blocks most red and near-infrared light, so uncover the area you want in the light.
2. Pick a distance, then keep it. Most panel sessions are 15 to 30 cm away. Closer concentrates the light; further covers more of the body. Keeping it the same each time keeps the dose the same.
3. About ten minutes. Most panel sessions are about ten minutes. Longer is not better by default. Remember the curve.
4. Consistency over intensity. The trials on this page ran sessions from twice a week to daily, for weeks or months.
5. Protect your eyes. Eyes closed, or the glasses on, whenever the light is at face height. Near-infrared is invisible, so your eyes do not squint against it.
6. Follow the guide in the box.

Pro owners: start with a preset, then use the touchscreen to shift the balance between red and near-infrared, or turn 960 and 1060nm up and down. Change one setting at a time and keep it for a few weeks before changing another.

Questions

Questions people actually ask.