Red vs. Near-Infrared (NIR) vs. Far-Infrared (FIR) Light Therapy: What is the Real Difference?
What is the difference between Red, Near-Infrared (NIR), and Far-Infrared (FIR) light therapies? Is one better than the other? Are there cases where a particular wavelength or micron range is more effective?
Should you choose a Full-Body LED therapy panel or a Far-Infrared Sauna? A Near-Infrared sauna? What about LED Pads, Infrared Pads, LED Bulbs or Infrared bulbs?
Generally Far-Infrared technology is used for heat therapy and detox, while Red and Near-Infrared is used for the non-thermal application of light for deeper penetration and sub-cellular up-regulation. This may be all people need to know for a basic understanding of the differences, however this blog will dive much deeper.
The main problem is that the benefits of Red, Near-Infrared, and Far-Infrared are very similar and often overlapping. People and companies are purposely conflating terms or making up new classifications like "full spectrum infrared" with no clear definition. This makes a very confusing situation, and we will attempt to sift through the data to find the truth.
So, with the popularity of alternative red and infrared light therapies soaring, it is important to clearly define the what these technologies are, the spectrums they emit, the penetration depths, the mechanisms for how they benefit the body, the types of devices, and how they are used.
Definitions of Terms:
“Red Light Therapy” often refers to usage of non-thermal LEDs or (cold) Lasers to deliver Red and Near-Infrared (NIR) wavelengths. The more precise term preferred by scientists is Photobiomodulation, where Photobiomodulation is specifically the science of the non-thermal interaction of light on the cells.
“Infrared Light Therapy” tends to use more heating devices like incandescent heat lamps, infrared heating pads, infrared domes, infrared saunas, and infrared sauna blankets. For Infrared, scientists prefer to term different ranges of Infrared by IR-A, IR-B, and IR-C instead of non-specific terms like “near-infrared” and “far-infrared light”.
The 250W Red Incandescent Heat Lamps are often marketed as "Red Light Therapy" or "Near-Infrared Light Therapy" as a misnomer since they emit a wide spectrum from Red to Far-Infrared. Regardless of the multiple inaccurate names, incandescent heat lamps can indeed be used as a cheap hack therapeutically, but there isn't much of a clear scientific category for them.
Thermal Image (Top) versus Picture (bottom). - A Red & NIR LED Bulb (Left) versus a 250W Incandescent Heat Lamp (Middle) Versus a 100W Far-Infrared Reptile Heat Bulb (Right). The LED light emits some brightness but produces very little heat. The Heat Lamp emits some visible light and a lot of heat. The Far-Infrared Bulb emits no light but only heat.
The solidification of the term Photobiomodulation in the medical literature clearly separates using optical radiation for non-thermal responses. So the first distinction we should make is that regardless of wavelength, the scientists are trying to create two categories of thermal and non-thermal light therapies.
And we can appreciate we even use the term “light” loosely because infrared is invisible to the human eye and doesn’t actually deliver any brightness.
Wavelengths of Red, NIR, and FIR
Sunlight has been the ultimate life-giving source of energy for billions of years; it is only within the past 80 years that humans have noticed the profound influence of the sunlight spectrum on our health.
The official “optical radiation” spectrum is between 100 nanometers (nm) to 1,000,000 nm. We can only observe the “visible spectrum” between 400nm (Violet/Blue) to 780nm (Red).
Even amongst different textbooks and publications and standards - the ranges for Red and Infrared can vary greatly (creating more inconsistencies and confusion). We will use the definition used in a new textbook on infrared light therapy, since those are ranges most relevant to distinguishing biological effects.
https://library.oapen.org/handle/20.500.12657/54423
Red light is between 600nm to 780nm
Near-Infrared or IR-A (Infrared-A, IR-A) is between 780nm to 1,400nm
Mid-Infrared or IR-B (Infrared-B, IR-B) is between 1,400nm to 3,000nm
Far-Infrared or IR-C (Infrared-C, IR-C) is between 3,000nm to 1,000,000nm
When only discussing infrared light ranges, we switch to talking about “micron” ranges. Where micron is short for micrometer with abbreviation μm (notice the prefix is the Greek letter “μ” spelt as “mu” and pronounced like "mew" and not a typical “u”). So, when you see “μ” just think “micro”, which is shortened to micron when talking about distance.
1 micron (μm) = 1000 nanometers (nm)
In other words, a micron is 1000 times longer than a nanometer. So when we talk about the Far-Infrared range, the wavelengths are much longer than when we typically talk about Red or Near-Infrared so we use the micron units instead.
Articles on infrared light might say that the entire Infrared range is from 0.78 microns to 1000 microns, and that also means it is 780nm to 1,000,000nm because we just multiply by 1000. And vise-versa if people are talking about nanometers, you just divide the number by 1000 to know the micron equivalent.
It is important to understand this these definitions and terminology especially when diving into the literature yourself and needing to understand the comparisons between microns and nanometers.
Spectrum of Red and Infrared Light Therapy
What is the spectrum of Infrared Light Therapy? The theoretical spectrum of infrared emitters has been well defined since the year 1900 by Max Plank.
The spectrum of an infrared emitter is directly determined by its temperature according to Plank’s laws and equations. All objects above 0 Kelvin (absolute zero) emit some infrared, which is why we can measure human skin temperature with an infrared sensing gun.
Infrared Thermal Cameras display the optical range between 7.2 and 13 microns, showing what the world looks like if we could "see" only infrared. This "infrared selfie" was taken in a mirror, showing that mirrors reflect infrared well too.
The theories set by Plank tells us that the light spectrum from a glowing piece of metal, from a hot stone, from our body, from a carbon infrared panel, the sun, and an incandescent bulb are all related by the same equation. The type of material used roughly determines the operating temperature of the infrared emitter in the devices, and thus the spectrum.
The glow of a infrared space heater or toaster oven element indicates the partical visible light from hot infrared emitters following Plank's laws. Infrared therapy is just a medical application of these common household technologies.
A carbon panel heater operates about 150-230 F (~360K), a ceramic heater about 350-450 F (~470K), and a tungsten incandescent bulb is 2700K.
Now let’s overlay some LED spectrums of 660nm and 850nm, and remember that LEDs are quasimonochromatic (quasi meaning “partly”) so even though the peak might be at 660nm or 850nm – there is some spectrum +/- 15 nm that you see sloping from both sides of the peak.
Then let’s overlay the ASTM Sunlight spectrum because we are often vying to re-create nature.
And we are going to “normalize” the spectrums (make the Y-axis meaningless by setting the height to 1) – this way we are just comparing spectral distributions – and we can discuss intensity separately later.
The chart is also on a logarithmic scale (not a typical linear scale) due to the extremely wide range of the infrared spectrum.
The peaks calculated by Wien’s Displacement Law are
- Carbon panel at 360K has a micron peak of 8μm (8000nm)
- Ceramic heater at 470K has a peak of 6μm (6000nm)
- Incandescent at 2700K has a peak of 1μm (1000nm)
- Theoretical peak of the Sun at 5500K is 0.5μm (500nm).
Even though some Infrared emitter companies can squabble about their supposed peaks and micron ranges, we can see the tremendous broad wavelength ranges for the Carbon and Ceramic heaters that overlap a lot. Where the LED will have distinct ranges that are more interesting to study to isolate biological responses to specific wavelengths.
Penetration Depths of Red and Infrared Light
One thing that makes Photobiomodulation (non-thermal) therapy so effective is the penetration into the body which we covered in-depth in a previous blog. The “optical window” of the skin is roughly defined as between 600nm to 1300nm, and beyond 1300nm water absorption takes over and leads to more superficial absorption.
This means we expect IR-B and IR-C to have much less penetration than the typical Photobiomodulation wavelength ranges – like noted in studies with diagrams like below.
A similar diagram is found here:
One study notes that the Red (633nm) penetration is about 3.5mm, the Near-Infrared 820nm penetrates to 8mm, and 10,600nm (10.6 microns) is only 20μm. So, we could say that Near-Infrared light has about 400 times more penetration than Far-Infrared wavelengths.
However, a recent editorial by Dr. Hamblin notes that even though the “ballistic” penetration of Far-Infrared (IR-C) is very shallow at only a few micrometers (μm), the effective penetration depth is 2 to 4 cm. [2] Authors theorize that the energy is transferred by the water molecules more indirectly that explains the non-photon penetration effects.
Many other studies on Far-Infrared light therapy also seem to corroborate that the effective penetration of far-infrared is 3 to 4 cm, despite its very shallow photon penetration. [3] [4]
This is similar to how researchers often note that Red and NIR LED benefits structures deeper into the body than the actual penetration depth [5], or how UV light can help promote Vitamin D synthesis which obviously affects the function of the whole body despite the lack of penetration.
So, for most light therapy effects, we need to be looking more at the biological mechanisms and benefits of these wavelengths rather than fixating on just the photon penetration depths.
Intensity of Red Vs Far-Infrared Light
When comparing Red Light Therapy and Far Infrared Light – the intensity or power output of these devices must be considered as a big part of the difference. Although strangely the intensity is overlooked when talking about Red vs FIR.
Remember that Joules are a unit of energy. 1 Joule is the amount of energy that raises 239 mg of water by 1 degree Celsius.[18] Where we should be familiar with the term Joules and how it relates to Power (Watts) from dosing calculations for photobiomodulation.
So, regardless of wavelength, absorbed radiation always has the capacity to raise the temperature of an object. Our skin and blood is uniquely designed to promote thermoregulation and will also excreet sweat when needed to cool off.
One Photobiomodulation study measured skin temperature increases with 810nm and 904nm lasers with increasing Joules and Watts. As they increased dose from 2 to 6 to 9 to 12 Joules, they found an increase in skin temperature of a total of 4 degrees C at the highest dose. They also found the 904nm had a much higher propensity to heat the skin than 810nm, which makes sense because 904nm has slightly higher water absorption and less penetration than 810nm. The point of the study was to understand safety of high intensity lasers, since they worried the "more power is better" marketing gimmick could eventually cause painful or deleterious skin overheating. [17]
Another study suggests to use photobiomodulation (Red and NIR 600-1400nm) with intensities less than 50mW/cm^2 to avoid skin hyperthermia (overheating). [13]
Much lower intensities of Far-Infrared are needed to produce heating in the skin due to its superficial absorption in the water. One study notes only "tens of mW/cm^2" is required to induce heating effects with Far-Infrared. [1] And that a non-thermal intensity of Far-Infrared would need to be only 0.1 to 5 mW/cm^2. [1]
So we can see that a thermal intensity of Far-infrared would be possibly greater than 5 mW/cm^2, and a thermal intensity of Red or NIR would be greater than 50 mW/cm^2.
Lets take a look at the power (Watts) of a few common devices for comparison.
Full Body Photobiomodulation vs Far-Infrared Sauna:
A typical single-person Far-Infrared Sauna utilizes 1300 W to 1500W, most of which we can assume is being converted to heat and infrared rays inside a decently insulated sauna.
Let’s say you have two “Joovv Elite” setups (on for the front and one for the back) for a total of 2x 248W (496W) of optical watts according to the manufacturer’s website.
Then we know that Red and Near-Infrared light is poorly absorbed and about 60% is reflected from the skin especially if standing 6 inches away. So perhaps only 200 Watts is absorbed, where more of the Far-Infrared is absorbed by water in the skin.
So, we have a potential difference of about 7x the absorbed power in an infrared sauna versus a typical full-body-LED-panel setup.
Are the heat effects from the Far-Infrared alone, the much higher power, or both? Probably both.
"NIR" Heat Lamp vs LED Lamp:
A typical “Near-Infrared” incandescent red heat lamp is 250 Watts. A LED Red Light Therapy Lamp from Amazon consumes an average of 20 Watts, and we assume at best only emits about 30% as optical energy so about 6 Watts emitted.
Once again, for a similar size bulbs we have the optical output difference of about 41 times the power from the LED versus incandescent. Can we even believe that the heat effects are only from the wavelength, and ignore the massive difference in power?
Infrared Pad vs LED Wrap:
The DGYao LED pad only consumes about 12 Watts. We know LED pads actually do warm up because they have no heat sinks or fans, but the DGYao pad runs "cooler" than most of the other pads we tested.
A similar size HealthyLine 1818 Far-Infrared mat is rated for 45 Watts and actually consumes about 54 Watts when we measured it with a Kill-A-Watt meter.
So even with infrared pads versus LED pads we observe a large difference in power output of 4.5 times more power. And we have heard reports that the LED pad users enjoy the heat effects more dominantly than the light effects.
*Case Study: I gave my mom the DGYao LED pad and the HealthyLine 1818 infrared mat. She has been using both regularly for over 6 months. She prefers the infrared heating mat more to relax her muscle pain.*
Why care about power and intensity?
We can see a pattern that the “heating” infrared devices not only deliver longer wavelengths, but much more power. Biological heating is always a function of power and intensity first, not wavelength.
For example, there are far-infrared textiles (clothing) that do not emit heat on their own, but are considered to be a far-infrared therapy regardless.[3]
And of course, we can appreciate that many “high power” LED Panels are vying to deliver instant gratification with feelings of warmth from high intensity.
So, if we want to control whether we want a thermal response or non-thermal response, then we need to understand the power and intensity of these devices, not just the wavelength. Some far-infrared technologies don’t illicit heat, and some high intensity red light devices will induce heating.
In understanding the differences between Far-Infrared versus Near-Infrared many people fixate on the wavelengths but seem to forget about intensity and power of these devices is a major factor.
Risks and Precautions:
Generally “red light therapy” photobiomodulation is considered very safe not only because of the wavelengths, but because it is low intensity delivered by non-coherent divergent beam LEDs. There are very rare cases of contraindications or risks, and are usually associated with excessive intensity as can be seen in our previous blog.
Far-infrared saunas are intended to induce sweating - so replacing water, minerals, and electrolytes is important – especially if it is a person’s first time they could become faint from dehydration or lack of minerals.
Repeated heating from any form including infrared devices can cause rare skin heating issues like erthyma ab igne, hyperpigmentation, or other skin irradiation issues. [7][16]
One study notes:
"IR-induced heat action can be pathological for the skin. When the skin temperature exceeds 39 C during IR irradiation, it can induce ROS generation and pathological effects through changes in structural integrity caused by enzyme induction in the skin. "[1]
Cheap infrared devices may lack temperature safety controls and overheat the skin, where it is documented that repeated or sustained skin temperature elevation can cause issues.
Even with intentional far-infrared heating, the medical applications of infrared heating devices are often careful not to exceed skin temperatures of 40 C for sustained periods (often lower), where at 45 C or higher is documented that skin damage occurs. [1] [10]
The risks with Red to Infrared for the eyes are also in cases of excess intensity, power, and heating called photothermal damage (as opposed to UV and Blue light causes photochemical damage even at low intensities). It is well documented that an increase of eye retinal temperature above 10 degrees C causes irreversible damage. [6] [8]
High heat and intensity is usually easy to avoid because your skin will give you warnings that it feels it is being overheated, however, extra precautions should be taken for individuals if they lack heat sensations.
Benefits of Infrared Heating:
The primary mechanism of most Infrared therapies is indeed heating. Which doesn’t always sound glamorous, but it does feel very nice and is often overlooked as a powerful healing modality.
Heat associated with Far-Infrared is known to relax muscles, reduce stiffness, improve circulation, activate metabolism, stimulate nociceptive receptors, and relieve pain. [9]
The FDA often approves/clears/registers infrared heating devices “for the temporary relief of minor muscle and joint pain and stiffness, or muscle spasm, the temporary increase in local blood circulation; and/or the temporary relaxation of muscle.”
https://www.accessdata.fda.gov/cdrh_docs/pdf10/K102149.pdf
Those are just the immediate, targeted benefits for far-infrared heating. We also know in the context of full-body infrared exposure like a sauna confers many more benefits. Infrared sauna therapy raises the core body temperature, induces sweating, and can assist in cardiovascular health, immune health, brain health, detox, and improve athleticism. [4][10]
While heat effects doesn’t sound like an enticing marketing ploy, we can appreciate the vast benefits it can deliver.
Non-thermal Mechanisms of Red and Infrared:
Several studies have noted that Far-Infrared confers both thermal and non-thermal effects, especially in the cases of far-infrared textiles that don’t emit heat. One study mentions the non-thermal mechanisms of Far-Infrared as:
“FIR may, therefore, excite molecules and cells (i.e. cytochrome-c-oxidase and intracellular water) and alter biological functions.” [11]
This revelation is mind-blowing, because these are exactly the same mechanisms that we thought were exclusive to non-thermal photobiomodulation such as LEDs and Lasers.
Indeed with longer-wavelength infrared preferentially being absorbed by water in the body, it can create EZ Water (Exclusion Zone Water) in the cells as defined by Gerald Pollack’s research group. This work is consistently cited in the infrared therapy literature as a primary mechanism for the non-thermal effects of infrared to improve cellular function. [12]
Where is it commonly accepted that Red and Near-Infrared have deeper penetration and direct actions on the Cytochrome C Oxidase to improve mitochondrial function, the Far-Infrared delivers similar non-thermal effects but focuses more on EZ Water mechanism.
Benefits of Red, NIR, and Far-Infrared Light Therapies
There are more similarities than there are differences in the benefits of Red & NIR versus Far-Infrared. Benefits we commonly associate with LED red light therapy like skincare, brain health, and wound healing can also be found for Infrared therapies too. [13][14][15]
One study also Co-Authored by Dr. Hamblin plainly describes this dillema:
"how can the biological effects of red and NIR absorption be so similar to those seen with FIR ?" [1]
Which is part of the confusion that we find very similar benefits for Red, NIR, and FIR – so it makes it harder to distinguish what we should choose as the “best” thing for a specific ailment.
So generally we should prefer Far-Infrared when needing direct tissue heating or detox with full-body devices. The usage of non-thermal Red and Near-Infrared LEDs and Lasers is used for deeper direct photon penetration and more subtle cellular mechanisms of healing.
The good news is that we if we have to choose only one modality, we shouldn’t worry about “missing out” on benefits of another - when used properly Red, NIR, and FIR can all deliver similar non-thermal benefits.
Full-Spectrum Infrared Sauna Therapy Conundrum:
"Full Spectrum Infrared" has become a popular term especially when selling saunas. Now that you are an expert in all of the information presented above, we can break it down.
The claim implies that Full Spectrum Infrared includes some Near-Infrared, Mid-Infrared, and Far-Infrared wavelengths. Manufacturers seem to achieve this with a smattering of different types of emitters in a single sauna like incorporating carbon, ceramic, quartz, or even tungsten infrared heaters, and maybe even throwing in a few Red or NIR LEDs in there as well.
Having all types of infrared would imply that you won't be missing out on any potential benefits as well as saving time by getting the full spectrum all from one device. Which of course we can find no study that verifies that "full spectrum sauna" delivers superior benefits to standard far-infrared sauna, or any studies about full-spectrum infrared sauna therapy at all.
The drawback of haplessly adding Near-Infrared into a Sauna is that Near-Infrared is poorly absorbed by the body and much is reflected away from the skin. In other words, Near-Infrared is an inefficient way of trying to heat the body, which may detract from the primary goals of sauna to induce sweating and detoxification.
Likewise, the clinical application of Near-Infrared is usually with skin-contact while the skin is still room temperature to allow for the best penetration and absorption. Using a vaguely defined 'full spectrum emitter" that you don't even know the intensity of Near-Infrared that even reaches the skin does not give much confidence that you have any chance of getting real Near-Infrared therapy benefits.
So, too much emphasis on "Full Spectrum Infrared" not only detracts from the heat therapy offered by Far-Infrared alone, but it likely does not mimic the clinical settings for the benefits of Near-Infrared in the photobiomodulation context.
As a counter point, we will end with a quote from Dr. Hamblin's recent editorial commenting on the existence of full-spectrum sauna brands that add in Red and NIR LED panels:
"The combination of FIR wavelengths and PBM wavelengths may provide additional physiological benefts." [2]
And we can note that this is an editorial (Opinion) article and this opinion was not backed up with any study or reference. In the disclosure statement he acknowledges that he is a scientific advisor for a brand that manufactures "full-spectrum" infrared saunas.
So the consumer is in the same boat as the top researcher in the field. We like to speculate that combining Red, NIR, and FIR in sauna could give an additional benefit - but we have no studies to back it up yet and we don't want to detract too much from the efficient heating provided by FIR alone.
Pros and Cons of Red vs NIR vs Far-Infrared:
Lets look at the more practical aspects of some realistic devices, rather than getting caught up in studies and mechanisms and lists of benefits.
Red and Near-Infrared LED devices are extremely convenient, affordable, and deliver profound benefits without heat (or minimal heat). They don’t take up much space and can often be used anywhere in the home conveniently. LEDs can be used instantly and treatments can be as short as 5 minutes to 20 minutes. Delivering light therapy from LEDs is extremely safe and using skin contact also helps with photon penetration. However, LED light therapy is very subtle because you don't feel anything during treatment, and the benefits will also be subtle and occur after consistent repeated usage. Often the overlooked immediate benefit of LED light panels is the bright light therapy aspect and improved sleep cycles.
Incandescent Heat Lamps are extremely cheap and a great way to experiment with heat and red light therapy. Finding a good grounded lamp and setting it up properly is important to avoid EMFs and burning yourself as these aren’t necessarily made with any safety considerations. Incandescent bulbs themselves heat up instantly, but will take time to heat up the body or the room if making a DIY sauna.
Far-Infrared devices like saunas, lamps, and mats are usually more expensive for the medical grade technologies. Saunas take up a lot of room, and even infrared pads must be laid out on a bed, couch, or floor. Infrared saunas and pads usually require some heat-up time of up to 20 minutes or more, then the session is usually at least 30 minutes. All of the costs and inconveniences of proper Far-Infrared therapy are certainly worth it for the immediate benefits like pain relief and long-term benefits like cardiovascular health and detox. But it does seem to take more cost and effort to get proper Far-Infrared into your routine.
Conclusions:
Comparing Red, Near-Infrared, and Far-Infrared wavelengths is difficult due to the complexities, nuances, and lack of thorough clinical research comparing them.
Trying to distinguish the differences of Red Light Therapy and Infrared Light Therapy in terms of penetration, mechanisms, and benefits is challenging due to the vast overlapping mechanics for how these light wavelengths interacts with the body.
The clear differences between Red, Near-Infrared and Far-Infrared therapies is with the total power (Watts) of the devices and the thermal effects. The thermal effects enable more circulation, skin and body temperature increases, temporary muscle and pain relief, and ultimately the cardiovascular and detox (sweating) benefits that far-infrared saunas are well known for.
However, heating is powerful and must be used cautiously to not overheat the skin, eyes, or cause potential unwanted effects.
Red and Near-Infrared LED devices are incredibly convenient for the low cost, low space needed, no heat-up time, and extremely safe and comfortable low intensity output. The profound benefits of low-intensity Red and Near-Infrared light delivered comfortably non-thermally cannot be understated, which makes it very easy to do routinely several times a week for long term benefits.
We found that instead of getting nerdy about wavelengths which often leads to confusing conclusions and the uprising of "full spectrum" gimmicks, we need to take a practical perspective on the actual devices that deliver these wavelengths.
Ultimately the best thing to do is to try these technologies yourself and start to feel the differences and see what works best for you. LED Bulbs, Incandescent Bulbs, and Infrared Bulbs are all cheap and easy to try. Then you can graduate to larger full-body devices or pads of your preferred technology.
A good resource for low-EMF far-infrared saunas is the Certified Saunas website.
A good place for affordable low-EMF infrared heat mats is HealthyLine (don't get the PEMF mats, just filter for Far-Infrared only).
https://healthyline.com/products/
Until then, we hope this blog filled with scientific references, pictures, diagrams, and practical device analysis can help close the knowledge gap to feel more confident to start trying and implementing any from of red and infrared light therapy to enrich your life, since they all clearly offer immense benefits.
References:
[1]
Vatansever F, Hamblin MR. Far infrared radiation (FIR): its biological effects and medical applications. Photonics Lasers Med. 2012 Nov 1;4:255-266. doi: 10.1515/plm-2012-0034. PMID: 23833705; PMCID: PMC3699878.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3699878/
[2]
Hamblin MR. Traditional or Infrared Saunas and Photobiomodulation: What Do They Have in Common? Photobiomodul Photomed Laser Surg. 2022 Sep;40(9):595-596. doi: 10.1089/photob.2022.0078. Epub 2022 Aug 30. PMID: 36040391.
https://pubmed.ncbi.nlm.nih.gov/36040391/
[3]
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8101933/#pone.0251282.ref002
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4493260/
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https://pubmed.ncbi.nlm.nih.gov/17566756/
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Youssef PN, Sheibani N, Albert DM. Retinal light toxicity. Eye (Lond). 2011 Jan;25(1):1-14. doi: 10.1038/eye.2010.149. Epub 2010 Oct 29. PMID: 21178995; PMCID: PMC3144654.
https://pubmed.ncbi.nlm.nih.gov/21178995/
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Haleem Z, Philip J, Muhammad S. Erythema Ab Igne: A Rare Presentation of Toasted Skin Syndrome With the Use of a Space Heater. Cureus. 2021;13(2):e13401. Published 2021 Feb 17. doi:10.7759/cureus.13401
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7971733/
[8]
http://photobiology.info/Rozanowska.html
[9]
Park YJ, Lee HK, Cho JH. Analysis of muscular elasticity according to infrared and ultrasound therapy by sonoelastography. J Phys Ther Sci. 2018 Aug;30(8):1024-1029. doi: 10.1589/jpts.30.1024. Epub 2018 Jul 24. PMID: 30154594; PMCID: PMC6110236.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6110236/
[10]
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4935255/
[11]
Bontemps B, Gruet M, Vercruyssen F, Louis J. Utilisation of far infrared-emitting garments for optimising performance and recovery in sport: Real potential or new fad? A systematic review. PLoS One. 2021 May 6;16(5):e0251282. doi: 10.1371/journal.pone.0251282. PMID: 33956901; PMCID: PMC8101933.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8101933/
[12]