Fundamentals
Red and near-infrared light has been researched for over 50 years. This page answers in three steps what is behind it. Without unnecessary jargon, but with evidence.
01 What is Red Light Therapy?
In short
Red light therapy is the application of red and near-infrared light at precisely defined wavelengths. Scientifically, it is called photobiomodulation. Unlike with a heat lamp, it is not about heating tissue. It is about certain molecules in the cell being able to absorb light energy.
The technical term explains the principle well: Photo means light, Bio biological, and Modulation to regulate – not to force. Nothing is removed, and nothing is burned. A small enough amount of energy is supplied so as not to burden the cell, but it is large enough to trigger something within it.
The effect was discovered rather by chance in the late 1960s. The Hungarian physician Endre Mester noticed that weak laser light accelerated wound healing in laboratory animals. For decades, the field was therefore referred to as "low-level laser therapy". Today it is known that it is not the laser itself that matters, but the wavelength and dose: A 660 nm photon from an LED is the same for the cell as a photon of the same wavelength from a laser1. Therefore, the more neutral term photobiomodulation has prevailed.
Both are red, both are lamps – and that's where the similarities end. A classic infrared lamp emits broadband radiation and contains large proportions of long-wave infrared. This light is almost completely absorbed by the water in the tissue and converted into heat. You clearly feel warmth, and that is precisely the purpose.
| Heat Lamp | Red Light Therapy | |
|---|---|---|
| Principle of Action | Heat | photobiological signal |
| Spectrum | broadband | defined wavelengths |
| Absorbed by | water in tissue | enzymes in mitochondria |
| You feel | distinct warmth | little to nothing |
| Dosage | according to warmth sensation | calculable in J/cm² |
You feel a heat lamp. Photobiomodulation must be measured.
The question remains: If not heat – what exactly happens in the body then?
02 How it works
In short
Red and near-infrared light is absorbed in the mitochondria by an enzyme: Cytochrome c oxidase. This enzyme is at the end of the chain by which the cell produces energy. When it absorbs light energy, this chain can work more freely13.
Almost every cell in our body contains mitochondria – the "powerhouses of the cell". They produce ATP, the universal energy molecule. Whether a muscle is working, collagen is being formed, or a damaged structure is being repaired: payment is always made with ATP.
This explains precisely why such diverse topics appear in research – from skin and muscles to wound healing. The mechanism in question is not found only in a single organ but in a component of practically every cell15.
Cytochrome c oxidase contains four metal-containing centers – two with iron, two with copper. These centers absorb light particularly well in narrow regions of the red and near-infrared spectrum23.
Under stress, oxygen deficiency, or inflammation, nitric oxide binds to the enzyme, blocking the site where oxygen should bind. This slows down energy production. Light can break this bond4.
Oxygen can bind again, increasing ATP production. At the same time, the released nitric oxide is available in the tissue as a signaling molecule – among other things, as the body's own vasodilator14.
The altered energy state is reported to the cell nucleus. There, different genes are read and different proteins are formed – for example, for repair, cell migration, and antioxidant defense15. This is precisely where the effects that can later become noticeable arise.
The best analogy for this
Light is not a charger, but rather a wake-up call. The energy for ATP still comes from food and oxygen. Light removes a brake and signals the cell to start its own programs.
Cytochrome c oxidase is considered the best-documented light acceptor – but it is probably not the only one. Additionally, light-sensitive ion channels in the cell membrane and effects on the structure of water at interfaces are being discussed1. Also open are the optimal dose for individual application areas and the question of how much skin type, age, and tissue thickness change the results. Anyone claiming that everything is completely clarified presents the state of research too definitively.
And why red specifically? Because only a narrow part of the light spectrum penetrates deep enough into the body.
03 Why Red and Near-Infrared
In short
Between approximately 600 and 1000 nanometers, there is a range where light is only minimally absorbed by skin pigment, blood, or water. This "optical window" is the reason why red light therapy uses red and near-infrared light – and not blue or green.
Light that is to enter the body must pass three important absorbers. Melanin (the skin pigment) primarily absorbs short-wave light. Hemoglobin (the blood pigment) strongly absorbs in the blue and green range. This is why blood appears red: red light is absorbed less intensely. Water (our main component) primarily absorbs long-wave infrared.
In between, there remains an area of low absorption. This is precisely where virtually all research on photobiomodulation takes place.
Both work through the same mechanism in the cell. The difference lies in how far they penetrate the tissue.
| Red Light | Near-Infrared | |
|---|---|---|
| Range | approx. 600–700 nm | approx. 700–1000 nm |
| Visible? | yes, vibrant red | no – appears almost dark |
| Primarily reaches | skin, collagen, hair follicles | muscles, joints, tendons |
| Often studied for | skin texture, wound healing, hair density | regeneration, musculoskeletal system |
On penetration depth: please read critically
"Penetration depth" is not a fixed number, but depends on how it is defined. It is common to refer to the point at which about 37% of the original intensity remains. The values depend on skin type, tissue, and blood circulation, and vary significantly in the literature67. What is most reliable is the order: Near-infrared penetrates further than red. Claims such as "penetrates 10 cm deep" usually refer to individual, extremely rare light paths – not an effective amount of light at that depth. We believe it is more serious not to promise a centimeter figure than to give a nice-sounding but misleading one.
And the dose?
One principle is worth knowing already: With photobiomodulation, more is not necessarily better. The effect follows a curve with an optimum. Too little light has no effect, too much can diminish the effect8. How a meaningful dose is derived from wavelength, irradiance, distance, and duration is explained on the technology page.
This explains the mechanism. The most important question remains: What does this mean in concrete terms?
04 What it helps with
Photobiomodulation is a broad research field with very diverse data. We categorize by strength of evidence, not by what sounds particularly appealing. We also note where the evidence is thinner.
A good reference point is a consensus paper from 2025, published in the Journal of the American Academy of Dermatology9. An expert panel evaluated the clinical application of photobiomodulation and found robust evidence for various ulcer forms, peripheral neuropathy, acute radiodermatitis, and androgenetic alopecia, among others.
Important Classification
The cited studies were predominantly conducted with clinical devices or lasers, often on individuals with a diagnosed condition and under medical supervision. They demonstrate that and how this field of research is being investigated. They are not a statement about what a home device achieves for an individual. heilys® devices are not medical products.
05 Honest Classification
A field that attracts both serious research and exaggerated promises needs clear boundaries.
We believe this clarity is an advantage. Those who can explain the limits of their product can also credibly convey its mechanism of action.
For your safety: Red and near-infrared light is non-ionizing. It does not carry enough energy per photon to damage DNA – unlike UV or X-rays9. What you should still pay attention to are eye protection, photosensitizing medications, pregnancy, and pre-existing conditions. More detailed information can be found on the safety page.
06 Frequently Asked Questions
Because the sensitivity of the human eye practically ends above about 780 nm. An 850 nm LED can run at full power and appear almost dark. This is normal and not a defect. This is precisely why protective eyewear is important for near-infrared: the glare that would otherwise make you look away is absent.
UV light has a completely different mechanism. UV photons carry enough energy to break chemical bonds, damage DNA, and accelerate skin aging. In contrast, the effects of photobiomodulation occur through the absorption of light by an enzyme. This requires red and near-infrared light. Therefore, devices for photobiomodulation operate without UV components.
For the described mechanism, yes, according to current understanding. The coherence of laser light does not play a crucial role in cellular absorption. Wavelength and dosage are decisive1. This is precisely why the term photobiomodulation has replaced "low-level laser therapy." LEDs have the advantage of uniformly irradiating large areas.
Usually just a slight warmth. Photobiomodulation is not a procedure with an immediate strong sensation. This distinguishes it from a heat lamp. It is to be expected that you feel little. It is not an indication that nothing is happening. Conversely: a strong sensation of heat is not a sign of quality, but usually an indication of too little distance.
A general number would be unserious, because the appropriate dose depends on wavelength, distance, and target tissue – and because more is not automatically better8. Research shows that regular, short applications over several weeks are more effective than infrequent, long applications. Follow your device's instructions and change the regularity rather than the duration.
Six wavelengths in the optical window, documented irradiance, developed in Germany and five years warranty.
15 works from specialist literature, each with DOI or PubMed ID for verification.
