photobiomodulation - October 22, 2023

What Should You Feel During Red Light Therapy? Is Heating NASA Photobiomodulation?

What should you feel during red light therapy treatments? Is it better to feel heat to confirm you got good value, or is feeling heat a sign that the device is too powerful?

How do we make sure we are doing true clinical grade red light therapy according to medical definitions, NASA, the FDA, and leading researchers?

You may want to know what to expect to feel during red light therapy treatments, especially if you are new to this topic. Or more likely, many people already using red light therapy should be checking the literature to make sure what they feel is in alignment with true clinical grade Photobiomodulation as described in the studies.

Summary: The patient typically doesn't feel anything at all with properly designed clinical studies and devices. Since the definitions of LLLT and PBM are clearly non-thermal according to every authority in the field, then typically barely any warmth should be expected. Feeling rapid heating is a sign the device is too powerful and hasn't been clinically studied for LLLT/PBM.

As always, you don't need to take our opinion on the matter. This blog we dig into the research to find direct quotes and descriptions of what is felt during true LLLT/PBM clinical treatments.

What is Red Light Therapy?

Red Light Therapy is the common name used to describe products and protocols that follow the science of Low Level Light Therapy (LLLT) and Photobiomodulation (PBM). The most popular wavelengths studied in these sciences are in the Red to Near-Infrared range of wavelengths 600nm-1100nm.

When brands and experts claim there are 7,000+ studies to back up their products, they are referring to the databases of LLLT and PBM articles. When brands and experts reference specific studies to make medical claims - they are usually referring to the studies in the LLLT/PBM literature.

While we love to get caught up in the parameters and dosing of Joules, Watts, Hertz, Nanometers, and more - often we don't hear about what should be felt during red light therapy treatments.

Official Definitions of Low Level Light Therapy and Photobiomodulation:

The medically-approved definitions for LLLT and PBM must be met in order for a study to be placed in the appropriate category on PubMed and other databases.

One article tells us the official medical definitions for LLLT and PBM:

"Low-level light therapy (LLLT) is defined as “Treatment using irradiation with light of low power intensity so that the effects are a response to the light and not due to heat. A variety of light sources, especially low-power lasers are used.” in the Medical Subject Headings (MeSH) Descriptor Data 2017.

Photobiomodulation (PBM) therapy is “A form of light therapy that utilizes non-ionizing forms of light sources, including lasers, LEDs, and broadband light, in the visible and infrared spectrum. It is a nonthermal process involving endogenous chromophores eliciting photophysical (i.e., linear and nonlinear) and photochemical events at various biological scales. This process results in beneficial therapeutic outcomes including but not limited to the alleviation of pain or inflammation, immunomodulation, and pro-motion of wound healing and tissue regeneration.” as a defined in Anders et al. [10].

It is now agreed that “PBM therapy” is a more accurate and specific term for the therapeutic application of low-level light compared with “LLLT”."

[1]

And we can appreciate clearly that the definition of LLLT is that the effects are "not due to heat" and the definition of PBM is that "it is a nonthermal process".

You can also read more in Dr. Anders' peer-reviewed paper discussing the definition of LLLT/PBM. It notes that the definitions were intentional to exclude any form of heating devices such as high powered lasers or heat lamps. [2]

Based on these broad definitions, you can use a wide range of wavelengths and light sources to do LLLT/PBM. It is very easy to meet this criteria, the only thing you can't do - is heating. Many high intensity devices causing radiant heat are no longer considered true LLLT/PBM.

You will literally never find any LLLT/PBM study that intentionally uses light for radiant heating - as it would be excluded and put into a different category.

Cold Light Therapy vs Radiant Heat Therapy:

The definitions of LLLT and PBM both include that they are the non-thermal (no heat) application of light to cause biological effects.

Hence, the popular term like Cold Laser that describes low-powered lasers intended for LLLT/PBM that don't cause significant heating like industrial lasers do.

A term like Cold LED was never defined, as it was assumed that LEDs would never be powerful enough to emit intensities high enough for radiant heating.

"Because LEDs operate at power levels below that which is considered by the FDA to constitute a medical hazard they have not been subject to therapeutic device regulation and this has paved the way for the commercial exploitation. "

[3]

"Low-energy laser irradiation has documented benefits in promoting the healing of hypoxic, ischemic, and infected wounds. In comparison to lasers, light-emitting diode (LED) technology generates negligible amounts of heat."

[4]

However, thanks to many brands that don't understand the science and influencers promoting high-powered "value" over optimal intensities, the LED Heat Lamp has indeed been invented in recent years. Which is a technological marvel that even the researchers didn't predict.

This innovation of LED Heat Lamps shouldn't be celebrated until it is fully proven, as heating technology is often contraindicated by the LLLT/PBM science:

"Heat is a compounding limitation in achieving optimal phototherapeutic effects. As surface heating of the skin increases, the biological effect begins to decrease."

[35] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9980499/

Heat Therapy is obviously different than Light Therapy. It has different mechanisms, dosing protocols, and safety considerations to do properly. If Red Light Therapy was meant to be a heat therapy, it would simply be called Red Heat Therapy or Radiant Heat Therapy. Like the NIR Heat Lamps that some people use for therapy, they aren't called NIR Light Lamps because their main mechanism is heating.

Dr. Hamblin's Definition of Photobiomodulation Therapy (PBMT)

The definition of LLLT/PBM is often reiterated in the Introduction or Background sections of most studies.

Dr. Hamblin wrote this definition in a future-dated 2024 article on photobiomodulation of the brain.

"PBMT generally uses red (620–700 nm) and/or near-infrared (780–1270 nm) wavelengths of light at an intensity that causes no tissue heating, and its activity is based on well-established biological and cellular mechanisms (de Freitas and Hamblin, 2016)."

[5]

This definition shows the crux of the problem with many modern LED panels on the market. The intensity must be low enough to not cause tissue heating to meet the LLLT/PBM criteria according leading researcher Dr. Hamblin.

Non-Thermal Intensities for PBM:

As Dr. Hamblin and many other publications have noted - using low intensities that don't cause tissue heating is a main point of doing proper LLLT/PBM.

In an article by Dr. Barolet, Dr. Christiaens, and Dr. Hamblin, they note the following criteria to help avoid excessive heating (and thus meeting the definition for PBM):

"Lower irradiance (<50mW/cm²) is less likely to induce skin hyperthermia leading to potential deleterious effects."

[6]

Naturally, the heating effects are often subjective and depend on bioindividuality like skin phototype, skin thickness, heat sensitivity, and blood circulation for thermoregulation. So this means everyone will "feel" heat at different intensities depending on many factors. As well, the size of the treatment area also matters when it comes to heating like a small laser vs a big panel.

"The photon intensity i.e., irradiance (W/cm2 or spectral irradiance), must be adequate. Using higher intensity, the photon energy will be transformed to excessive heat in the target tissue and, using lower intensity, photons absorption will be insufficient to achieve the goal."

[7]

The quote above tells us that high intensity will lead to the photons being converted into heat. Thus, not contributing to the Joules/cm^2 for proper dosing of red light therapy. The energy (Joules) calculation only works for Photochemical reactions and not for Photothermal reactions.

"Within a certain range of parameters, perhaps between 1 and 100 J/cm2, and at power densities from 1 to 100 mW/cm2, this linear reciprocity applies. However, beyond this range, reciprocity does not appear to apply."

[7]

Now this quote makes more sense, since at >100mW/cm^2 a significant amount of photons will be converted to heat. So you cannot use the standard dosing calculations for high intensity (>100mW/cm^2) light therapy - especially because we know heat therapy has no reciprocity (no linear dosing calculation) like PBM has.

Generally, large LED devices with intensities > (greater than) 50mW/cm^2 would lead to not meeting the definitions of LLLT/PBM, and thus not being able to dose it properly, not being backed by 7,000+ studies, and not expect the same safety and efficacy of devices that follow the science that are < (less than) 50mW/cm^2.

The NASA LED Therapy

In a marketing gimmick as worn-out as my Tempur-Pedic Foam Mattress, many LED panel manufacturers will claim their technology was originally developed by NASA.

However, lets take a look at a couple of quotes describing the NASA LED therapy in published peer-reviewed literature.

"NASA developed LEDs to offer an effective alternative to lasers. These diodes can be configured to produce multiple wavelengths, can be arranged in large, flat arrays (allowing treatment of large wounds), and produce no heat. It is also of importance to note that LED light therapy has been deemed a nonsignificant risk by the FDA; thus, FDA approval for the use of LEDs in humans for light therapy has been obtained."

[8]

The NASA LED therapy is described as producing no heat. As well we can see that non-heating LEDs are non-significant risk by the FDA.

Here is another desription of the NASA LED, in a study actually using a device that came from the NASA research mady by Quantum Devices, Inc.

"Heat production is a concern of laser therapy. In contrast, the LED arrays, originally developed for NASA plant growth experiments in space and used in our studies, produce virtually no heat and have attained FDA approval for non-significant risk status.

...

Thus, even if LED should prove to increase cellular temperature to a fraction of a degree higher than normal, and if it should elicit further cellular events, heat is not likely to be a major factor in the therapeutic treatment with LED."

[9]

So we can appreciate the nuance here that inevitably the application of low Intensity or Joules of any wavelength will make fractional temperature increases on the tissue - however this is rarely felt by the patient and does not affect the therapy.

As this quote confirms and thousands of studies also confirm - the benefits of LLLT/PBM are from light therapy, not activating heat therapy mechanisms.

So if you are using high intensity LED panels as a heat therapy, you are no longer doing the NASA-developed LED light therapy - which is described clearly as being non-thermal.

FDA True Medical Grade LLLT/PBM:

The FDA recently issued guidelines for their definition of LLLT/PBM and criteria for device applications and approvals:

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/photobiomodulation-pbm-devices-premarket-notification-510k-submissions

In both the Introduction and Background section the FDA notes that LLLT/PBM is non-thermal.

Introduction:

"The device is designed to deliver a non-heating dose of light energy into the body to provide clinical benefit to the patient."

(pg 5, FDA draft guidance for PBM, Jan 12, 2023)

Background:

"For the purpose of this guidance, the term “photobiomodulation” is defined as the application of light at an irradiance that does not induce heating with the goal of altering biological activity."

(pg 6, FDA draft guidance for PBM, Jan 12, 2023)

So if you want to do the FDA Recognized version of true medical grade Photobiomodulation - then you need to make sure it is "non-heating" and "does not induce heating" as they clearly state. It is so important to be non-thermal that they say it twice in the same document.

And this explains why many LED Heat Lamp manufacturers are registered as medium-risk Class II heat lamps under the ILY code - not as non-thermal PBM devices. The FDA still maintains an exclusion that low-risk non-thermal LEDs for general wellness do not require registration.

And again, we could make a drinking game out of how many times the emphasis is on having low power, low intensity, or low irradiance (aka low power density, mW/cm^2) as the primary factor to make sure there is no heating for true LLLT/PBM.

High intensities are the enemy of true medical grade LLLT/PBM, despite the paradoxical marketing that everyone needs the "highest intensity" device to be effective.

Endre Mester's Definition of Photobiomodulation Therapy (PBMT)

Endre Mester is often credited as the grandfather of LLLT/PBM for his discovery and research starting in the 1960's.

"The first scientific description by Prof. Endre Mester about fifty years ago outlined the effects of low dose laser interaction with tissues describing the non-thermal therapeutic benefits of biophotonics energy [2,3,4]."

[10]

So even dating back to Dr. Mester, we know that this therapy has always been a non-thermal usage of light. Amazingly, many brands and experts are trying to re-write a 60+ year old definition so that Red Light Therapy matches their marketing narrative of selling overpowered LED Heat Lamps.

What Do You Feel During True Red Light Therapy?

Lets see what the research tells us you should feel during red light therapy.

LLLT/PBM Textbook - no tangible changes:

A 2018 Textbook on LLLT/PBM published by SPIE with co-authors including Dr. Hamblin, Dr. Ferraresi, Dr. Huang, Dr. Freitas, and James Carroll had this to say about the user experience:

"PBM does not often cause any visible or tangible changes in the tissue during the moment of light delivery, which leads some patients to doubt that a real effect could be evoked by that “little light,” as they might say. It can be difficult to make them understand, or even accept, the photochemical and photobiological events that occur inside them during the therapy."

[11]

They describe the experience that there are no visible or tangible changes during treatment. The usage of the word "tangible" would imply there is nothing felt like heat on the skin.

The user naturally doubts the effectiveness of true "cold" light therapy because they cannot feel anything during the treatment. We can understand why many people want to use light therapy as a heat therapy because they seek that instant gratification of feeling something during treatment.

The textbook reassures the reader that there are Photochemical effects that leads to all the benefits of LLLT/PBM, despite the lack of Photothermal (heat) effects.

No Sensation With True Light Therapy:

One study used 633nm and 870nm LED clusters on the forehead to treat the brain emitting 22.2 mW/cm^2 for 13.3 J/cm^2 per area to treat TBI and improve cognition.

This is what they had to say they felt during treatment:

"No sensation of heat or pain was reported during the LED application to the skin or scalp." [12]

Another study using cold lasers for acupuncture had this to say:

"There is usually no sensation to help determine whether or not a point has been stimulated with laser as it is with needle acupuncture." [13]

And another study with cold laser for acupuncture also said this:

"Typically, patients do not feel any sensations when a low-light laser is used,²³ although some patients have reported a tingling or “light touch” sensation.^24" [14]

One Low Level Laser Therapy had this description for what is felt during treatment:

"The powers used in laser therapy are by definition too low to cause tissue damage by either heating or acoustic effects. Nonetheless, it seems possible that the same effects that are claimed to promote beneficial processes could also be detrimental. However, neither experience nor literature searches reveal substantive risk. Patients do comment at times about transient warmth or “tingling” during or shortly after treatment. However, in our experience this has occurred in both active and placebo subjects." [15]

This quote is interesting as both the treated and control groups feel warmth or "tingling" - perhaps because the placebo effect encourages the people to produce some internal response despite not feeling anything. As well they directly note the therapy must use power that is low enough to not cause any heating.

Mild Warmth with Clinical Grade LED Panels:

Two published articles refer to an LED panel emitting 50mW/cm^2 of 830nm wavelength. This is how they described the sensation:

"The majority of student-athletes receiving 830 nm LED-LLLT indicated having achieved an excellent result, namely a reduction in pain and inflammation, while also noting pleasantly mild surface heating of the skin." [16]

And in another publication:

"Within 5–10 min, a gentle warming of the face is also felt as the microvasculature brings more blood to the superficial dermis through vasodilation." [17]

So this is likely the maximal intensity that is appropriate. Only a mild heating is felt after 5+ minutes of exposure. This may not even be from direct radiant heat at all, but a warming sensation through Nitric Oxide release causing vasodilation (local blood flow increase).

If you are feeling immediate or rapid skin heating with a high intensity LED panel, it is likely it is too powerful to be considered true clinical grade LLLT/PBM.

Remember that this uses the least heating 830nm wavelength and using Red would actually cause more heating at this intensity.

Blinded Studies - No Feelings From Both Groups

The standard for clinical trials is to have a placebo group, and have both the treated group and placebo group "blinded" (i.e. unaware) if they are getting the placebo or true treatment.

One study describes the importance of blinding in studies this way:

"Blinding is critical to clinical trials because it allows for separation of specific intervention effects from bias, by equalising all factors between groups except for the proposed mechanism of action." [18]

Placebo groups are very easy to do with traditional drugs, as you can simply give the patient a sugar pill or some other inert substance in the same size and shape of the drug.

However, proper blinding with devices is very challenging, as you need to replicate the device and simulate the sensation of the treatment without actually doing the treatment.

For example, one review article on Cupping therapy for obesity notes that a blinded placebo was impossible - as you cannot replicate a false sense of cupping without actually doing cupping. [19]

Similarly, it is difficult to have "blinding" from heat therapies. Since obviously a person should feel if they are experiencing heat or not and would know if they are in the placebo or treatment group.

With LLLT/PBM - due to the nature of being non-thermal - you can do blinded studies. With invisible Near-Infrared wavelengths this is even easier as there is nothing to see either, and with Red wavelengths you can simply blindfold the patients in both groups.

One study using PBMT LED/Laser cluster for muscle performance had this to say:

"During PBMT and placebo applications, subjects used opaque glasses that blocked their view. In addition, PBMT did not cause any sensitive stimuli (heat, cold, skin irritation, and pain) that could provide participants with information about the dose or treatment being administered." [20]

One study used a combination Laser and LED cluster for fibromyalgia had this to say about the blinding procedure for placebo:

"The assessors, therapists, and patients were blinded. The assessors of the study were unaware of a patient’s allocation and the PB MT-sMF device was preprogrammed to active or placebo mode. The sounds emitted from, and information displayed on, the device’s screen were identical, regardless of the programmed mode. In addition, the device used had no thermal effects,26 enabling the blinding of the therapists and patients to be maintained throughout the treatment." [21]

Studies with the Vielight device are able to be double-blinded because there is no heat or sensation to be felt during treatment. They simply strap on another Vielight device and don't turn it on for the allotted amount of time. [22][23]

A recent study covered by the MedCram YouTube channel describes using 670nm light at 40mW/cm^2 on the backs of patients:

"The LED array was positioned 400 mm from the participants back, surrounded by a shield that rested on the participant’s skin, to prevent light leakage, and to blind the participant to which group they were randomised into. The placebo group underwent the same procedure, except the LED array was not switched on during their intervention OGTT." [24]

Since there is no heat expected from 40mW/cm^2 and non-contact LED treatment, they were able to have a successful blinded placebo control group by simply not turning on the LED panel for the placebo group. And yes, 15 minutes of non-contact non-thermal LED exposure at 40mW/cm^2 was indeed effective. [24]

Having properly blinded placebo-controlled trials for LLLT/PBM has led to the strength of the science proving that it is effective. If it were a heat therapy, this would be very challenging to do properly blinded trials.

Is Cold Light Therapy is not Effective?

Clinical grade red light therapy is defined to be non-thermal, with most studies reporting no sensation of heat (or anything at all) ( ideally <50mW/cm^2). High intensities (~50mW/cm^2) will naturally produce a mild warming sensation after several minutes. Excessive intensities (>100mW/cm^2) will lead to rapid heating and no longer meet the definition of true LLLT or PBM.

"The thermal effect of radiation does not appear when the irradiance is below 100 mW/cm² (in our study, the irradiance of 53 mW/cm² was used and the absolute increase of 1.5°C was observed in blood temperature, which recovered to the baseline values within 3 minutes). Considering the fact that the temperature during the analysis in the multiplate aggregometer reaches 37°C, we assume that the mentioned above increase of 1.5°C has a negligible effect on the observed results." [26]

Many studies even monitor skin and tissue temperature changes to make sure it is minimal. With many only reporting less than 1-3 degrees C change, which would be hardly even felt as warmth by most people especially as the heating is slow and gradual. [28][29][30][31][32][33][34]

Dr. Hamblin writes in one article:

"By now everybody will accept that PBMT using red or NIR radiation (or indeed blue and green wavelengths) can produce biological effects by a photochemical mechanism as opposed to a photothermal mechanism." [27]

Ironically, the people selling and promoting high-intensity LED heat lamps have clearly not accepted this fact. Perhaps people doubt the efficacy of non-thermal LLLT/PBM as detailed in 7,000+ articles. Perhaps the salespeople think they are smarter than the doctors and researchers using non-thermal light therapy in clinical studies.

However, these high powered devices are far beyond what has actually been studied in full-body red light therapy trials and higher than natural sunlight intensity for these wavelength ranges. We don't know the long term effects of chronic usage of intensities higher than nature intended, even if they feel good in the short term.

It is a bait-and-switch deception when high-intensity (>100mW/cm^2) brands make medical claims based on LLLT/PBM research, and then sell you a glorified LED heat lamp that doesn't fit the clinical definitions or dosing to achieve those benefits. If they are proudly selling a LED Heat Lamp, then they need to advertise it accordingly and stop refercing non-thermal LLLT/PBM studies for their safety and benefits.

Conclusion: Value is Effectiveness, not Excess Power

At GembaRed we will stick to the established science that has confirmed effectiveness and non-significant risk for low-intensity non-thermal LED light therapy.

Our definition of "value" is that products are safe and effective in accordance with the science, not some sales gimmick of getting the most Watts per Dollar.

A high-intensity LED Heat Lamp holds no value to me, not only because it lacks the science, safety, and efficacy of true LLLT/PBM - but because I can get NIR Incandescent Heat Lamps for $10, or get a Beurer heat lamp for $80, I already enjoy my Presto Radiant Heater in the winters, and radiant heat therapy is redundant to my routine usage of my infrared sauna and infrared heating pads. If I want a true "light" therapy then I want it non-thermally in accordance with the science to activate the photochemical mechanisms, not photothermal mechanisms.

So while influencers will sell you on gimmicks of high intensity and tell you how much they enjoy LED heat therapy for their affiliate payments - they suddenly have diminished their therapeutic "value" and brought them into a mundane low-cost category of competing with generic heat lamps and infrared heating pads.

Which actually makes LED Heat Lamps an overpriced (and inefficient) form heat therapy, rather than a valuable nuanced therapeutic of cold LLLT/PBM. Impressively, they manage to help you improperly dose two types of therapy now, as you aren't doing Photobiomodulation Therapy or Heat Therapy correctly with these LED Heat Lamps.

Consider that the converse of this blog is also true. If we had found dozens of studies and definitions explaining how LLLT/PBM was indeed a heat therapy - then we would have designed our products and education accordingly. We have found that the mere definition itself has restricted the 7,000+ articles to support a "cold" light therapy, not a "hot" light therapy.

Bonus Section: More Quotes of Non-Thermal Red Light Therapy

Here are a few more quotes I had collected for this blog clearly stating that LLLT/PBM is non-thermal (no heating).

It is rather difficult to ignore these definitions if you have read enough studies. One starts to feel it is rather important to be non-thermal if only for the sheer repetition of seeing it so often in studies. And obviously being non-thermal is actually important to activate the correct mechanisms, be absolutely safe with minimal side effects, increases penetration, allows you to use skin contact, and reduces the risk of excess ROS and biphasic dose response.

We have to wonder if any experts promoting high intensities have ever read a single LLLT/PBM study to have missed these clear definitions, or more likely they conveniently ignore information that doesn't match thier sales narratives.

Quotes:

"Because of the low power without causing temperature rise or change in the gross tissue structure, as well as the advantage of being non-invasive, it has been broadly applied to wound healing, pain relief, healing after peripheral nerve injury, decreasing inflammation, which have been explored in both animal models and human patients (Oron U,et al. 2014; Johnstone DM, et al. 2016; Cheng Y, et al. 2018)."

https://www.sciencedirect.com/science/article/abs/pii/S0014483524004408?via%3Dihub

"A new terminology established in 2015 defined PBMT as a non-thermal and non-ionising light therapy applied in the form of light amplification by the stimulated emission of radiation (laser), light-emitting diodes (LEDs), and/or broadband irradiation in the visible and infrared spectra.⁹

...

Trials were only included if they estimated the effects of any type of PBMT (laser class I, II or III or LED), including all wavelengths. Other light-based therapy such as laser acupuncture and high-intensity laser (laser class IV) were not included because they are not PBMT.⁹^,¹⁰^,³⁰^"

https://www.sciencedirect.com/science/article/pii/S1836955320300643?via%3Dihub

The above quote is from a systematic review of many articles on PBMT. Notice how high-intensity lasers are excluded, as high intensity devices do not fit the definition of PBMT.

"LLLT is an athermic photochemical modality, where red or near-infrared light is used to stimulate tissue healing and reduce pain and inflammation.^22–24"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9528593/

With "athermic" being a fancy way of saying non-thermal.

"Low level laser therapy (LLLT) in the visible to near infrared spectral band (390-1100 nm) is absorption of laser light at the electronic level, without generation of heat."

https://pubmed.ncbi.nlm.nih.gov/30614743/

"The beneficial effects of PBM are thought to occur primarily by inducing a photochemical reaction in the cell, instead of generating a thermal effect. 11"

https://www.jkslms.or.kr/journal/view.html?doi=10.25289/ML.2020.9.2.89

"The effect is not thermal, but rather related to photochemical reactions in the cells."

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD002046.pub2/abstract

"The medical use of low level laser (LLL) irradiation has been occurring for decades, primarily in the area of tissue healing and inflammatory conditions. Despite little mechanistic knowledge, the concept of a non-invasive, non-thermal intervention that has the potential to modulate regenerative processes"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2830167/

"The NIR delivered through tPBM is absorbed by a mitochondrial enzyme and chromophore, cytochrome c oxidase (CCO), and is only minimally dissipated as thermal energy [17,19]. "

https://www.mdpi.com/2304-6732/10/1/90

"This nonionizing nonthermal irradiation is absorbed by endogenous chromophores (particularly in the mitochondria), eliciting photophysical and photochemical events via various biological pathways"

https://onlinelibrary.wiley.com/doi/10.1111/odi.14618

"Photochemical reactions happen when the energy of photons made by the laser in the molecules of the cells causes chemical reactions in the molecules without changes in temperature.53"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7118506/

"These lasers emit no heat, sound, or vibration. Instead of generating a thermal effect, LLLT acts by inducing a photochemical reaction in the cell, a process referred to as biostimulation or photobiomodulation"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065857/

"Light energy parameters that do not cause photothermolysis or thermal damage but still alter biological function are considered photobiomodulatory.28,57"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8887026/

"Unlike other laser treatments, photobiomodulation is not an ablation or heat-based treatment. Considering the mode of action, it is more like photosynthesis."

https://www.sciencedirect.com/science/article/abs/pii/S1572100023004817?via%3Dihub

"Photobiomodulation employs monochromatic light in the optical region of red and infrared lasers to treat various tissues in a non-destructive and non-thermal fashion [9]."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4833286/

"Photobiomodulation (PBM), previously known as low-level laser therapy (LLLT), is defined as the application of non-ionising radiation in the form of light with the intent to heal. PBM employs the use of photons at a non-thermal irradiance to elicit photochemical and photophysical events to alter biological activity [7,8]."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8537491/

"LLLT has athermal and superficial effects (3–4 cm) and is known for its photobiological effects (photobiomodulation) that stimulate or inhibit biological processes depending on the delivered energy dose (Arndt-Schultz law) [11]. "

https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-023-07599-0

"is interesting to compare the two treatments discussed above (PBM and IR emitting bioceramics) with wIRA. The big difference of course is that PBM and bioceramics were designed to produce no detectable heating effect in the tissue."

https://www.ncbi.nlm.nih.gov/books/NBK593483/

"Phototherapy is, in its broadest sense, the use of light for any kind of surgical or nonsurgical treatment, but it is the athermal and atraumatic therapeutic application of light which is now accepted as the working definition of phototherapy."

https://www.researchgate.net/publication/269748891_The_photobiological_basics_behind_light-emitting_diode_LED_phototherapy

"Photobiomodulation utilizes monochromatic (or quasimonochromatic) light in the electromagnetic region of 600∼1000 nm for the treatment of soft tissues in a nondestructive and nonthermal mode"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4256027/

"LLLT, which uses light energy to modulate cell and tissue physiology to achieve therapeutic benefit without a macroscopic thermal effect (sometimes termed cold laser)."

https://pubmed.ncbi.nlm.nih.gov/19913903/

"Since LLLT does not generate destructive heat, safety relates mainly to potential eye damage"

https://pubmed.ncbi.nlm.nih.gov/19913903/

"With the upcoming of powerful LEDs operating in the R-NIR spectrum the nomenclature had to be adjusted accordingly: Today the acronym LLLT stands for the generalized term low level light therapy, where low indicates that the light intensities and doses used are non-thermal, i.e., biostimulatory."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7154450/

"Photobiomodulation therapy can be an interesting candidate, because it is a technique involving cell manipulation through the photonic energy of a non-ionising light source (visible and NIR light), which produces a nonthermal therapeutic effect on the stressed tissue."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8122620/

"NIR lasers have good penetration through skin and soft/hard tissue without heating (hence cold lasers), making them suitable for pain relief, wound healing, tissue regeneration, and as anti-inflammatory treatments60."

https://www.nature.com/articles/s41598-022-14812-8

"Certain forms of PBM treatment are also referred to as low-level light therapy (LLLT), since it utilizes light at a low power (0.1 to 0.5 W output at the source) to avoid any heating of tissue."

https://www.spiedigitallibrary.org/journals/neurophotonics/volume-3/issue-03/031404/Review-of-transcranial-photobiomodulation-for-major-depressive-disorder--targeting/10.1117/1.NPh.3.3.031404.full?SSO=1

"The reason why the technique is termed LOW-level is that the
optimum levels of energy density delivered are low when compared to other forms of laser therapy as practiced for ablation, cutting, and thermally coagulating tissue. In general, the power densities used for LLLT are lower than those needed to produce heating of tissue, i.e., less than 100 mW/cm2, depending on wavelength and tissue type (Huang YY et al., 2009)."

https://www.researchgate.net/publication/221920419_Laser_in_Orthodontics

"The typical power output for a low level laser device used for this therapy is of the order of 10-50 mW, and total irradiances at any point are of the order of several Joules. Thermal effects of LLLT on dental tissues are not significant, and do not contribute to the therapeutic effects seen."

https://www.researchgate.net/publication/221920419_Laser_in_Orthodontics

Thank you for reading all the way to the end of this bonus section. Because you understand the basic definitions of LLLT and PBM, you are now a better expert of light therapy than most brands selling high intensity LED panels and the influencers promoting them.

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