Wavelengths in red light and infrared light therapy are often mentioned as numbers: 630 nm, 660 nm, 850 nm. It may sound like small details, but this is precisely where the difference between “mostly skin” and “more depth” often lies. When you know what the numbers mean, it becomes easier to choose equipment and treatment that suits your goal, whether it concerns skin, recovery, sore joints or a stubborn muscle.
What does “nm” mean, and why does the number tell us something about the effect?
“nm” stands for nanometer and indicates the wavelength of light. The wavelength determines, among other things:
- how much light is absorbed in the skin’s uppermost layer
- how far the light can typically penetrate into tissue
- which biological “receivers” (chromophores) are affected most
In photobiomodulation (red light and infrared light therapy), the goal is not to heat up the tissue, but to give the cells a light stimulus that can support natural processes such as energy production, repair and dampening of inflammatory conditions.
Red light (630–660 nm) and infrared (850 nm): same family, different behavior
630 nm and 660 nm lie in the visible red range. 850 nm lies in infrared and cannot be seen with the naked eye, although you can often sense a faint glow from the diodes.
Both ranges lie in what is often called the body’s “optical window,” where light generally has better opportunity to pass through tissue than many other wavelengths. But they still behave differently in practice.
Red light is typically absorbed more at the surface, partly due to the skin’s pigment and blood’s coloring substances. Infrared at 850 nm often has higher relative transmission in tissue, so a larger portion of the energy can reach deeper structures.
This does not mean that 850 nm “goes directly through” the body. Much light is still dampened in the first millimeters. The difference is that 850 nm usually leaves more usable energy deeper in the tissue than 630–660 nm at the same output power.
630 nm: often chosen for skin and superficial issues
630 nm is often associated with skin-related goals: glow, texture, minor irritations and general skin support. The slightly shorter wavelength can provide clear superficial stimulation, which suits keratinocytes (skin cells in the epidermis) and processes in the upper layers well.
In practice, 630 nm is often seen in equipment for face and skin, where one wants a targeted effort without “shooting too deep.” This is also part of the reason why many masks and skin-oriented applicators prioritize red light around this range.
When talking about “collagen,” it is especially the interaction with fibroblasts in the dermis that is interesting. Red light can support fibroblast activity and thereby the skin’s structure over time, when the dosage is appropriate and use is regular.
660 nm: close to 630 nm, but often used as the “classic” for red light
660 nm lies close to 630 nm, and the effects overlap greatly. Nevertheless, 660 nm is often referred to as one of the most used wavelengths in the red light field, partly because it is widespread in research and in many professional protocols.
In skin and superficial tissue, 660 nm is often used with focus on supporting repair, skin firmness and calm in reactive areas. Several studies suggest that 660 nm can stimulate fibroblasts and be relevant in contexts where one wants to support wound healing and tissue building.
Many experience in practice that 630 nm and 660 nm feel similar in use. If you face the choice between them, it often makes more sense to look at the device’s quality, power (irradiance), treatment area and documentation, than to believe that the 30 nm alone determines everything.
After a brief clarification, choosing red wavelength often becomes a question of goal and area:
- Facial skin
- Superficial areas
- Scars, structure, glow
- Local care for minor issues
850 nm (infrared): when the target sits deeper
850 nm is typically used when one wants to affect tissue under the skin’s uppermost layer: muscles, tendons, structures near joints and deeper connective tissue. In many contexts, 850 nm is associated with recovery and pain relief, precisely because depth is often the limiting factor.
A simple way to think about it: If the area can be “reached” with red light, red light may be enough. If the problem feels like something that lies under the surface, 850 nm often makes better sense, simply because more light reaches deeper down.
This is also the reason why many body applicators and larger pads combine 660 nm and 850 nm, so you hit both surface and depth in the same session.
When 850 nm is used in a targeted manner, it is often seen in these situations:
- Muscles and tendons: recovery, soreness after training, stress conditions
- Joints and stiffness: support for calm in tissue around knee, shoulder, wrist and back
- Deep pain: when the “point” feels difficult to reach with superficial treatment
- Local circulation: experienced by many as a warm, relaxing effect without actual heat treatment
How big is the difference in penetration in reality?
It is tempting to put fixed centimeter numbers on it, but penetration depends on more things than wavelength alone:
Skin type and pigment play a role, because melanin dampens especially shorter wavelengths more. Distance matters a lot: a few centimeters can make a big difference, because light spreads. And contact matters: an applicator close to the skin reduces loss to the surroundings.
There is also a difference in light source. LED devices typically shine broader and less “concentrated” than laser, while lasers can often deliver more focused energy to a small area. Both types can give good results, but they are often used for different purposes.
Here is a practical overview that can be used as a rule of thumb when you look at 630 nm, 660 nm and 850 nm:
| Wavelength | Visible? | Typical focus in use | Where in the body do you usually aim? | Typical applications |
|---|---|---|---|---|
| 630 nm | Yes | Surface-oriented red light | Epidermis and upper dermis | skin care, glow, minor superficial issues |
| 660 nm | Yes | “Standard” red light in many devices | Dermis and superficial tissue | collagen support, scars, skin calm, superficial recovery |
| 850 nm | No | Depth-oriented infrared | Deeper connective tissue, muscles, tissue near joints | sore muscles, joint issues, recovery, deeper pain relief |
The table describes the direction, not a guarantee. The right match is still about dose and consistency in use.
Why do many devices combine 660 nm and 850 nm?
The combination is popular because it covers more broadly. Red light can be strong at the surface, while infrared can reach deeper. This provides a more versatile treatment, especially on larger areas like back, thighs, knees and shoulders.
There is also research that suggests that combinations of red and infrared can give a stronger overall biological response than one wavelength alone in certain models. In practice, this means that many choose a pad or wrap with both wavelengths when the goal is both well-being and function.
Heat Sense and other players in Denmark offer precisely often CE-approved equipment where red light and infrared are included together, because it provides a “two-in-one” treatment that suits home use and clinic environments.
How to choose wavelength based on your goal
Start by defining what you want to achieve and how deep you assess the issue lies. Then choose wavelength and equipment accordingly, and be realistic about the time horizon. Red light and infrared light therapy is often a process where regularity means more than turning everything up at once.
A simple way to decide:
- Choose area: face/skin, or muscle/joint
- Assess depth: surface (red) or deeper (infrared)
- Look at the device’s data: power, treatment surface, timer, CE approval
- Plan routine: same time, same area, same duration
- Adjust according to response: less time if skin becomes irritated, more continuity if the goal is recovery
Dosage: why “more” can give less effect
Photobiomodulation is often associated with a biphasic response. This means that an appropriate dose can be stimulating, while too high a dose can give a flatter response or irritate the tissue.
In everyday life, dosage is about three things: how powerful the light is at the skin (irradiance), how long you treat, and how often you do it. Two devices with the same wavelength can feel very different if one delivers significantly higher power or has a different distance to the skin.
If you work with skin, it often makes sense to start gently and see the skin’s response. If you work with a deep area, patience is important, and many choose longer sessions or more frequent use, as long as it feels comfortable and does not give unwanted reaction.
Safety and practical considerations in home use
Red light and infrared in the strengths normally used for photobiomodulation are generally considered safe and without UV-related risks. Nevertheless, there are good habits that increase safety.
Do not use powerful light sources directly in the eyes, and follow the manufacturer’s instructions about glasses, distance and time. If you are in treatment for serious illness, are pregnant or have light sensitivity, it makes sense to clarify the use with a relevant health professional.
CE approval, clear documentation and possibility for support mean a lot, especially when the equipment is to be used often. For many, it is an advantage to choose a Danish supplier with stock in Denmark, so it is easy to get guidance about wavelengths, use and maintenance when facing the choice between 630 nm, 660 nm and 850 nm.
