How Wavelength Affects Dosing For Red Light Therapy: The Weight of Photonic Energy
PBM researchers have recently introduced new Red Light Therapy dosing variables that promise to be more consistent and universal!
They have the potential to reduce the variability of dosing values, and to reconcile the effects from different wavelengths.
The secret is that precision dosing is now weighted by Photonic Energy.
The new dosing system recognizes that shorter wavelengths will have stronger biological effects than longer wavelengths.
In other words, shorter wavelengths will require less J/cm^2 weighted by their higher energy per photon. Longer wavelengths require more J/cm^2 to compensate for their lower energy per photon.
Introduction:
There are many variables to consider when dosing with red light therapy.
Some of the main ones include:
- Intensity (mW/cm^2) and Exposure Time (seconds or minutes)
- Energy Density a.k.a Fluence (J/cm^2)
- Total Joules (J)
And that is not even to mention the influence of wavelength selection, pulsing, and cumulative dose response.
However, one missing consideration for dosing has been the Energy Per Photon, although it is implied by the wavelength selection.
Thus, PBM researchers in the industry have decided that we need even more variables to create more precise dosing protocols.
Recent PBM articles describe the two new variables of Photonic Fluence (p.J/cm^2) and Einstein Dose (E). These dosing variables take J/cm^2 and weights it by multiplication with the Energy Per Photon (eV).
"By employing advanced photonic fluence and Einstein dosing, more precise results can be achieved, accurately aligning within the Arndt–Schultz curve."
[1]
These new units could help make dosing protocols more consistent, however they require some understanding of physical chemistry to fully appreciate.
In the near future, we will see many studies and dosing standards using these new variables. It is important to learn the basics that we will cover in this blog to stay up to date on the latest PBM literature.
Photonic Energy vs Joules Energy:
Energy units like Joules (J) and Joules Per Centimeter Squared (J/cm^2) have been the dosing standard in LLLT/PBM for many years.
The Joule unit is primarily useful to understand physics, electronics, and engineering.
However, Joules are not always directly applicable to photochemistry or photobiology. Our cells have no special sensor to determine how many Joules they have absorbed, and thus must respond in a specific way.
Chemical reactions from light more specifically rely on the number of photons absorbed, and the energy value of those individual photons.
The total energy (i.e. Joules) delivered is directly correlated to the photonic energy. This is why Joules is somewhat useful for dosing, but is inconsistent.
Total Energy = Number of Photons Times the Energy Per Photon
Rather than looking at Joules alone, we should be looking at the constituents of Joules to better understand the biological responses to light.
Marbles Analogy Part 1:
For example if we have a jar of marbles. We could determine the weight of all the marbles by simply weighing the entire jar (minus the weight of the empty jar).
Or, the weight can be determined by the multiplication of the number of marbles by the weight per marble.
Both ways reach our minimum understanding of the total weight, but it may be more useful to know the exact contents inside the jar.
Similarly, if we are only using Joules for dosing but don't understand the number and energy of the photons, then we could be missing key information to understand photochemical responses.
Electron Volts (eV):
Electron Volts (eV) are a unit of energy, so they are directly proportional to Joules (J).
1 eV = 1.602176565 * 10^-19 J
However, we can see that 1 eV is many orders of magnitude smaller than a Joule.
The eV unit is useful to understand energy on a molecular, electron, and photonic scale.
Thus, the Energy per Photon is quantified easily in terms of eV.
Wavelengths and Frequency:
Radiation is quantified by a wavelength (nm) and corresponding frequency (Hz). They are inversely proportional. Longer wavelengths have lower frequency, shorter wavelengths have higher frequency.
Not to be confused with frequency of pulsing which uses the same term Hertz (Hz). Hertz (Hz) just means "per second", so it can be applied to anything that repeats itself on that scale. It is important to note the context when considering any scientific units.
Quite literally, a Wave-Length is the distance between two waves. Naturally, since there is less distance between waves and they travel at the same speed, then there are more waves per second with shorter wavelengths.
A pictorial example below. Not to scale. Just to illustrate the concept.
Wavelengths and Photon Energy:
There is also a 3rd property intrinsic to radiation, the energy per photon.
Longer wavelengths have lower energy per photon. Shorter wavelengths have higher energy per photon.
Higher frequencies intrinsically require more energy to be produced. Take note that sometimes studies may use the term "high frequency" to imply "higher energy per photon".
Thus, the eV of a photon is constant determined by the wavelength. Regardless of the other parameters, the eV is fixed by the wavelength.
The conversion requires Planks Constant and the Speed of Light divided by the Wavelength. So the eV per photon is always inversely proportional to the wavelength based on these constants.
"Since photonic energy and wavelength (λ) have an inverse proportional relationship, photons emitted from different active medium sources will have differing energy values." [2]
Some eV per photon of common wavelengths include:
- 350nm (UV) = 3.54 eV
- 480nm (blue) = 2.58 eV
- 630nm (red) = 1.97 eV
- 660nm (red) = 1.88 eV
- 810nm (NIR) = 1.53 eV
- 830nm (NIR) = 1.49 eV
- 850nm (NIR) = 1.45 eV
- 1064nm (NIR) = 1.17 eV
We can see the eV drastically decreases as the wavelength increases.
There are online conversion calculators so you can input custom wavelengths to find the eV:
https://www.kmlabs.com/en/wavelength-to-photon-energy-calculator
Joules vs Number of Photons:
Given the new understanding of energy per photon, that means the composition of Joules will be different depending on the wavelength.
For example 10 Joules of Red (630nm) will have 1.35x less photons than 10 Joules of NIR (850nm). (1.97eV for 630nm divided by 1.45eV for 850nm)
Since Red is higher energy per photon, it takes less photons to make up the same amount of Joules.
10 Joules of 480nm Blue will have 1.37x less photons than 10 Joules of 660nm Red (see the Header photo at the top).
That means longer wavelengths like Infrared always have more photons per Joule than the shorter wavelengths. Due to their low eV, it requires more photons to deliver the same amount of energy.
Marbles Analogy Part 2:
Imagine we have two jars of marbles both at the exact same weight of 10 kilograms.
However, in one jar the marbles weigh 0.1 kg each. The second jar the marbles weigh 1 kg each.
So, the first jar would have 100 marbles, and the 2nd jar would have only 10 marbles. If we only knew the total weight, then we would miss out on important details on the inside. We would not appreciate the differences of the contents within.
In this analogy, the lighter marbles (left) are the longer wavelengths, as they have lower energy per photon. The heavier marbles (right) correspond to shorter wavelengths, as they have higher energy per photon.
Photochemical Activation and Dissociation Energy:
When a molecule absorbs a photon, the molecule momentarily enters an excited energy state. To resolve the higher energy state, the molecule may conventionally:
- Re-emit light like fluorescence
- Undergo a chemical reaction or change
- Increase in kinetic energy (i.e. increase in vibrational or rotational movement, measured in a bulk material as an increase of temperature)
For a photochemical reaction to occur, the photon must provide enough Activation Energy to the molecule that absorbed it. Or, when breaking a molecular bond it is referred to as Dissociation Energy.
Insufficient eV would lead to no reaction, as it does not provide required energy to reach the threshold to support a chemical reaction. The absorbed photon would be converted to heat, rather than promoting a molecular change.
"For example: a 405 nm source has an eV of 2.9, whereas a 810nm
source has an eV of around 1.45. The molecular effects of
being struck by a more highly energetic 405nm photon are
highly likely to be quite different to that achieved by the more
pedestrian 810 nm photon." [3]
Thus, shorter wavelengths are well-known to be more photochemically active because they supply more eV per photon.
"The reasons are in energy of photons and nature of chemical bonds. Much higher energies are harmful and break molecules; much lower energies are not distinguished from the thermal noise (see examples below)." [4]
For example, Niels Finsen (awarded the Nobel Prize in 1903 for his work on light therapy) would refer to UV and Blue as the Chemical Rays as he observed they had higher photochemical activity.
The Red and Infrared wavelengths did not have much chemical activity, and would mostly observe thermal effects from them.
https://archive.org/details/39002010758374.med.yale.edu/page/n13/mode/2up
Photon Energy Thresholds:
The eV required to break common molecular bonds in biology are listed in this study.
For example, to break a C-N (carbon - nitrogen) bond takes 3.0 eV. [2]
Ultraviolet at 350nm has 3.54eV, which is why it can break some molecular bonds. When molecules are broken down they may become unstable, ultimately acting as a form of Free Radicals or ROS in the body.
However, Red and Near-Infrared are all less than 2 eV. Meaning they are insufficient to meet the threshold to break these bonds.
In other words, even if we used high Intensity (mW/cm^2) and/or high Dose (J/cm^2) then that does not matter so much in photochemistry.
"Even low-intensity light of a suitable frequency will lead to electrons being emitted whereas high-intensity light below this threshold frequency will have no effect. " [5]
If the eV per Photon is insufficient to reach the threshold of activation or dissociation energy - then no reaction will occur. Regardless of the Intensity or Joules. Thus, the energy will be converted into heat rather than facilitating a chemical reaction.*
It is worth noting that the opposite is also true. Higher eV per photon does not mean a "better" effect. As long as the eV meets the minimum threshold or higher, the reaction is the same. It may be prudent to use the minimum eV that meets the threshold to avoid collateral damage of creating unwanted reactions.
*section footnote: Of course, many chemical reactions are driven by being provided heat energy, regardless of the source of the heat. But this being a discussion of photobiomodulation and not heat therapy, then that consideration is outside the scope of this blog*
Marble Missiles:
In my last marbles analogy, we will consider our two jars from before.
- One jar with 100 marbles 0.1 kg each (representing longer wavelengths, lower eV).
- One jar with 10 marbles that are 1 kg each (representing shorter wavelengths, higher eV).
The same total weight of 10 kg (representing the same total joules of energy), yet very different compositions inside.
Now lets say we start throwing the marbles individually at a wall. Since it is known that only one photon is absorbed by a molecule at a time, and multiple simultaneous photon absorption is a rare quantum occurrence. [6]
"The second law of photochemistry or the Stark-Einstein law states that one absorbed photon can excite only one molecule.10 Typically, one absorbed photon excites exactly one molecule, though multiphoton activation, wherein the quick succession of sequential absorption of lower energy photons activates a single absorbing species, is an exception to this." [7]
The 0.1 kg marbles make no permanent dents on the wall. It is a special wall that requires a certain threshold of force or momentum to leave a dent.
The 1 kg marbles do make dents on the wall, because they have significantly more momentum upon impact and have met the threshold to cause permanent damage.
Even though we threw the same total weight from each jar, and there were many more of the 0.1 kg marbles - the 1 kg marbles made a more significant impact. Even with significantly less total marbles.
And with my special wall: even if we threw 2 kg marbles at the wall, the dents would be exactly the same as the 1 kg marbles.
Similarly, we could be examining J/cm^2, but ignoring the impact of the Energy per Photon on how it affects dosing for biochemical effects. Photons of higher energy could have a much stronger impact, but is not being properly accounted for with the standard dosing variables.
Photonic Fluence and Einstein Dose:
In the new dosing terminology, photons with higher eV are given more weight when considering its effect on a photobiology.
So, the Photonic Fluence (p.J/cm^2) is proposed as being the:
J/cm^2 multiplied by the eV of the wavelength(s)
Thus:
p.J/cm^2 = J/cm^2 x eV
The Einstein Dose is then the p.J/cm^2 divided by 4.5:
E = p.J/cm^2 / 4.5
They decided that 3 J/cm^2 of 810nm equals 1 Einstein. [1]
Typically that means there is great significance to the 810nm wavelength and 3 J/cm^2 to make it the base unit of a new system.
The Theory of how Photonic Joules will Revolutionize Dosing:
These two doses are expected to have a different effect:
- 9 J/cm^2 of 660nm
- 9 J/cm^2 of 850nm
Because we have based our original system on standard Joules, this is hypothesized as a main reason why there is such wide variability in dosing so far.
For example, one article treating osteoblast cells found the optimal dose for 655nm was 1 J/cm^2. But for 808nm the optimal dose was 5 J/cm^2. We can easily assume the wide variations in dosing could be caused by differences in wavelength-specific properties like photonic energy. [8]
However, under the new dosing system, these two doses are now expected to have similar effects:
- 9 p.J/cm^2 of 660nm (2 Einstein)
- 9 p.J/cm^2 of 850nm (2 Einstein)
Why? Because now we have taken into consideration the impact of eV per photon with the dosing structure.
Photonic Fluence Study:
The equivalence of photonic fluence was introduced in the study titled: "Thermodynamic basis for comparative photobiomodulation dosing with multiple wavelengths to direct odontoblast differentiation". [9]
They treated isolated odontoblast cells (cells that produce dentin for teeth) with 447, 532, 658, 810, 980 and 1064 nm wavelengths.
They used 3 J/cm^2 for all wavelengths one set of trials. Then they used 4.6 p.J/cm^2 for all wavelengths in another set of trials.
They found that while the standard dosing J/cm^2 had widely variable results, the 4.6 p.J/cm^2 showed closer equivalent effects for most of the wavelengths.
810nm was used as the reference wavelength due to having the best response and a long history of being the preferred wavelength for PBM.
Wavelengths 447nm and 1064nm showed the best improvement with the new dosing system.
The 532nm, 658nm, and 980nm were less responsive to the new system, but that was attributed to the responsiveness to the types of cells they were treating. [9]
So, it is proposed that Photonic Joules and Einstein would lead to more consistent dosing standards. Although there is limited comparative research on this topic so far, and the original study showed it did not work perfectly for all of the wavelengths.
Wavelength Harmonization:
The new dosing paradigm also integrates the concept that all the wavelengths have similar effects, as long as the dosing is applied properly. As opposed to the common marketing gimmick that specific wavelengths can only treat specific conditions.
The intent is that if one laboratory is using 810nm for clinical studies and another laboratory is using 850nm, the differences in dosing can be harmonized by using Photonic Joules and Einstein to get similar effects. Leading to less variability of dosing results and recommendations.
"A major advantage of this approach is its ability to enable harmonized dose interpretation and communication that can be universally implemented with accessible PBM wavelength devices that may otherwise be globally restrictive." [10]
If one study uses 1060nm and your device only has 850nm, you would theoretically get the same effect by using equivalent p.J/cm^2 as the study with your 850nm device.
"This novel dose system has been recently applied to the dosing recommendations by the World Association for Photobiomodulation Therapy (WALT) to increase practical implementation irrespective of individual wavelengths or devices that are available globally while preventing overdosing and enabling dose combination with various wavelengths [51]." [11]
So rather than getting an overpriced device that likely only has a small % of 1060nm anyway, this can reduce the expense and confusion and hype around "novel" wavelengths that inevitably get introduced in the future. As long as Photonic Joules are considered, all wavelengths would theoretically get a similar response.
Full Body Dosing with Photonic Joules:
In one study on PBM on human patients with persistent brain fog from a popular virus of unknown origin, they used Photonic Joules to consider dosing. [10]
The device was a NovoThor bed delivering 20.2 J/cm^2 per session. It uses 50% Red 660nm and 50% Near-Infrared 850nm. So, they calculated 34.3 p.J/cm^2 and 7.6 Einstein dose. [10]
How do we calculate it ourselves?
Well we split 20.2 J/cm^2 by the percentage of each wavelength. It is easy for this case as it is an equal split, 10.1 J/cm^2 for each wavelength.
- Red 660nm: 10.1 J/cm^2 * 1.88 eV = 19.0 p.J/cm^2
- NIR 850nm: 10.1 J/cm^2 * 1.45 eV = 14.7 p.J/cm^2
So the total p.J/cm^2 is 19.0+14.7 = 33.7 p.J/cm^2.
The reason why my number doesn't match the study is likely from rounding error for eV data. The study used 1.9 eV for 660nm Red and 1.5 eV for 850nm NIR. So, they were rather generous in rounding up the eV values.
Then divide by 4.5 to get Einstein. Which I get 7.5 E.
Red Light More Stimulatory than Near-Infrared:
Notice in the above example: Even at equivalent Joules, the Red is now given significantly more weight for dosing.
Since Red is a shorter wavelength with higher eV, it is expected to have a stronger photochemical response.
One article compared various wavelengths on various cell types, and found that Red light produced a more pronounced effect than 808nm Near-Infrared. They noted that 1064nm had the least effect.
"Red light seems to more rapidly stimulate ROS production, mitochondrial activity and cell survival than 808 nm."
...
"while 1064 nm light does not show any distinguished effects." [12]
Another article discusses the higher energies of Red compared to NIR, and how that affects the mechanisms of action.
"Red light (600–700 nm) displays higher photon quantum energy (2.07–1.77 eV) than NIR (808 nm = 1.53 eV), and can more easily induce tissue electrochemical changes. On the other hand, NIR light increases mostly a molecular vibrational state, which may lead to a transient thermal effect (at least 2 °C in tissues with thickness from 3.0 to 5.0 mm) and increased metabolic activity. Therefore, comparing the effects of different wavelengths should consider their photon energy, an issue that is often missing in many studies" [13]
As the quote above article implies, Red light has more direct electrochemical effects. Near-Infrared is more indirect, and would likely lead to transient (temporary) temperature flux as its mechanism of stimulation.
Thus, it makes sense that the new Photonic Joules would encourage higher J/cm^2 for the lower eV Near-Infrared wavelengths to compensate for their lack of chemical stimulation. Shorter wavelengths like Red are comparatively "more effective" due to their higher eV, so they can use lower J/cm^2 to reach the same effect.
These studies have specifically recommend considering photon energy for PBM effects, which the new Photonic Joules dosing now incorporates.
Violet and Green PBM for Pain Relief:
The Erchonia® medical laser company has been utilizing this concept for many years and publishing peer-reviewed research on their devices.
Their most recent laser uses Violet (405nm) and Green (520nm) lasers at low power (5mW for Violet and 7.5mW for Green). [14]
In one study, they treated 130 humans with chronic neck pain for 13 minutes per treatment. The patients were split into 3 groups. One receiving Violet+Green, One Red+Green, and one Red-Only.
They found the Violet+Green group had the best response. Although all groups showed improvement.
Their justification for this effect is based on using higher energy photons and more responsive target chromophores.
"In this study, the short wavelengths utilized were 520 nm and 405 nm, with photon energies of 2.4 eV and 3.0 eV, respectively. These observed photon energies are notably higher than those commonly employed in low-level laser therapy (LLLT); in fact, the violet 405 nm wavelength (3.0 eV) has twice the energy of an infrared wavelength of 808 nm (1.5 eV). " [14]
https://pmc.ncbi.nlm.nih.gov/articles/PMC10567292/
This is in stark contrast to the common preference to use deeper-penetrating Near-Infrared at higher intensities and doses to treat musculoskeletal pain.
Again, reinforcing the methodology of this new dosing system to consider the effects of higher eV photons.
Perilous Harmony:
When you want to use equivalent dosing as the studies, all you need to do is deliver equivalent p.J/cm^2 or Einstein for more consistent results.
Regardless of the study using a single wavelength or multiple wavelengths that don't match your specific device, the dose can now be harmonized by the Einstein dosing system.
Under this theory, a device with 2 wavelengths would have the same effect as a device with 7 wavelengths - as long as they both compensate the exposure to deliver the same Photonic Joules and Einstein Dose.
Unfortunately, with many modern panels having 4+ wavelengths, that will be a lot more math required to calculate the Photonic Joules or Einsten dose.
- First you would need to know the accurate J/cm^2 (assuming you are provided accurate intensity information by the manufacturer).
- Then multiply J/cm^2 by the percentage of each wavelength in each panel to get the J/cm^2 for each wavelength.
- Then multiply each value by the eV for the corresponding wavelengths.
- Then add it all back together.
- There you have Photonic Joules dose.
- Then you divide by 4.5 to get the Einstein dose.
And for a broad spectrum lamp, this may mean taking an integral of the spectrum to find the average eV.
While theoretically this system will lead to more consistent results and less confusion, there are many more steps making it tedious and prone to calculation errors. Even in my first example we demonstrated rounding errors with eV values.
Nitric Oxide Photodissociation CytoChrome C Oxidase:
We can now connect this concept to the main mechanisms of Photobiomodulation.
Many studies will mention how Nitric Oxide (NO) may be bound to Cytochrome C Oxidase (CCO). The absorption of light may lead to photodissociation of the NO, which was inhibiting the CCO. Thus allowing more efficient metabolism.
"It is assumed that this absorption of light energy may cause photodissociation of inhibitory nitric oxide from CCO [20] leading to enhancement of enzyme activity [21], increased electron transport [22], oxygen consumption, mitochondrial respiration and ATP production [23]. " [15]
"When light reaches CCO and is absorbed by the enzyme, electrons are excited. It has been suggested that PBM in the red and NIR wavelengths induce NO photodissociation [15]. Thus, PBM can dissociate NO from CCO, leading to an enhancement of CCO activity. " [16]
The NO-CCO bond is likely rather weak, although I have not found the estimated eV for dissociation.
Red and NIR wavelengths are relatively low eV compared to Blue and Ultraviolet. As the following quote explains, Red-NIR light likely does not effect cellular chemistry directly.
"As a consequence, the effects of a shorter-wavelength photon striking a molecular target are markedly different from those experienced at longer wavelengths. In red- to NIR-wavelength regions, there is insufficient energy to break the chemical bonds of many common tissue constituents" [17]
This is what makes Red and NIR light very safe, as it cannot have a direct destructive effect on molecules in the body. The only known risks are thermal (heat) based.
"However, red and NIR photons have relatively low energy, limiting the range of processes they can initiate. " [18]
Other theories state photodissociation could be occurring in the blood:
"However, it should be noted that some authors have suggested that photodissociation of oxygen from hemoglobin32 or NO from myoglobin33 could be a relevant mechanism in PBM." [19]
However, it is well established that non-thermal Red and NIR light is causing some sort of photoactivation. The photons get converted into promoting some biological activity, rather than being converted into heat.
"On the other hand, when a laser or other appropriate light source is used on tissue at low incident levels of photon energy, none of that energy is lost as heat but instead the energy from the absorbed photons is transferred directly to the absorbing cell or chromophore, causing photoactivation of the target cells and some kind of change in their associated activity. " [20]
This means our understanding of the direct photochemical mechanisms of Red and NIR is still elusive. Other proposed mechanisms may be modulating ion channels or building Exclusion Zone water.
No Action Spectrum for PBM?
In other words, there is no defined action spectrum for Photobiomodulation. The weighting function is based entirely on eV per Photon, rather than a specific biological response spectrum.
The plant growth industry has primarily moved away from Watts and Joules dosing in favor of photonic flux and action spectrums. In that way PBM science is far behind on adopting a similar shift in dosing.
"A pivotal shift in understanding plants emerged in the 1970s. Scientists argued that quantifying radiation energy (wattage) alone wasn’t sufficient. Instead, they proposed measuring the number of photons emitted instead of wattage, because the impact on photosynthesis is more directly and precisely measurable." [link]
The plant growing industry uses the Quantum Yield to add a weighting function based on the action spectrum for photosynthesis. [21]
"The Yield Photon Flux YPF weights photons in the range from 360 to 760nm based on plant's photosynthetic response." [link]
"For this reason, biological weighting functions such as Photosynthetically Active Radiation (PAR) or average plant response (also known as the McCree curve or plant sensitivity curve) are used in photobiology [26]. The weighting functions take the spectral response of a biological system into account and, therefore, can only be used for specific applications. " [22]
The plant growth industry focuses on the action spectrum that is specific to the biology of plants, rather than just the energy per photon.
As opposed to Human and Animal light dosing, where the PBM industry has not defined any specific action spectrum.
Niels Finsen also made this remark in his 1901 book. Meaning that over 100 years later, we still do not have a specific action spectrum for animals.
https://archive.org/details/39002010758374.med.yale.edu/page/n13/mode/2up
For example, if we know certain wavelengths around 750nm or 950nm were more inhibitory or less effective, then a weighting function based on biological responses would be applied to adjust the dose accordingly.
Less Emphasis on Penetration Depths:
Lets say that we know Red light penetrates roughly half as deep as Near-Infrared.
Then if we are using Red light for a deep tissue treatment, then we would double the dose (J/cm^2) to try to get enough energy to the deeper tissues.
That would be an informal weighting function based on the penetration depths of wavelengths. Which many people are already subconsciously considering when dosing.
However, the Photonic Joules theory takes this in the opposite direction. Red has higher eV than Near-Infrared. Which means we would use less J/cm^2 for a Red dose compared to Near-Infrared.
For example, one human study looked at muscle fatigue comparing 660nm or 830nm. All the parameters were made equal (same intensity and J/cm^2). As they explain in the quote below, they were surprised that both Red and NIR performed equally.
"Surprisingly, no differences were observed in peak force and average force between red and infrared LLLT. Laser radiation at infrared wavelengths penetrates better through human skin than red wavelengths [32], and for this reason we expected that the results with infrared LLLT would be better than with red LLLT in this trial. With this perspective, further studies are warranted to investigate the specific mechanisms by which each wavelength acts in delaying skeletal muscle fatigue." [23]
They conclude that there are likely specific mechanisms aside from penetration depths that lead to the similarity of results.
This new dosing theory is reinforcing that the effects of PBM are indirect and systemic. It does not rely on deep penetration, instead it relies more on the photochemical activity of the wavelengths.
For example, UV is superficially absorbed, yet we know it is crucial for systemic health by producing Vitamin D and releasing Nitric Oxide from the skin. Similarly Red wavelengths are more superficial than NIR, but can drive beneficial effects with more photochemical activity and systemic mechanisms.
Or, as we already do in the standard system, we need to consider the Photonic Fluence that actually reach the target tissues for direct stimulation. So we still need to take into account penetration depths with the new system.
Absorption and Reflection Weighting:
Another consideration would be weighting doses based on Absorption and Reflection spectrums.
With our dosing calculator, we integrated a 2.5x factor when considering skin reflection losses from non-contact delivery of Red-NIR light. Again, this could be considered an informal weighting factor for dosing.
However, skin reflection from light is a spectrum that depends on wavelength. Red and NIR have the highest reflection of around 60% for Caucasian skin and 40-50% for darker skin. [24]
Blue and Green Light only have 20-40% reflection from Caucasian skin. And in Dark Skin it is only Zero to 10% reflection of blue and green. [24]
So this could be a double-whammy of effects. Not only do the shorter wavelengths have higher photonic energy, but they are also much more efficiently absorbed.
The Photonic Joules dosing system is good for this, as it promotes lower doses for the shorter wavelengths based on the higher eV. When in reality these wavelengths are also more stimulatory because they are more efficiently absorbed.
Wavelengths longer than 1400nm have high water absorption and minimal reflection for all skin types, which is why they are perceived as heat even with relatively low intensities.
Synergistic Effects of Multiple Wavelengths:
Studies have shown that multiple wavelength treatments can have synergistic or interfering effects.
The effect of 2 wavelengths are often not merely the addition of 2 effects, but may be new effect entirely.
"Different combinations of wavelengths (serial or simultaneous) have synergistic and/or interfering effects on the observed light-dependent increases in NO." [25]
However, those studies were based on the older system of using equivalent J/cm^2.
Perhaps the new Photonic Fluence dosing system would normalize these types of results. More studies would be needed on multiple wavelengths with the new dosing system to confirm.
WALT Standard Dosing:
Learning the basics of Photonic Joules and Einstein dosing is key, as we will see more studies and standards referring to this new system of dosing.
For the treatment of oral mucositis, the new dosing standard has already been implemented by the World Association for Laser Therapy (WALT).
In a 2022 position paper, they listed the consensus dosing recommendations for cancer side effects in terms of Einstein and Photonic Joules dosing. [26]
The typical recommended doses are between 1 to 2 Einstein.
The position paper has recommended wavelength ranges for specific types of treatments. For example, for intra-oral (inside the mouth) treatments they recommend Red 630nm-680nm. For transcutaneous (through the cheek) they recommend NIR 800nm-1100nm.
However, they do state that other wavelengths are allowable with suitable dosing adjustments and monitoring for non-thermal effects.
"Other wavelengths (400-1100 nm) may be used with suitable adjustment to dosing, but treatments must be monitored to ensure a non-thermal (< 45 °C) process." [26]
And of course, they remind us that proper intensity and exposure time is still important in the new system:
"A common misconception is that energy (in J) or energy density (J/cm2) is all that is necessary to replicate a successful treatment, irrespective of the original power, power density, and duration parameters (14, 15)." [26]
A common misconception indeed, especially amongst influencers promoting high intensity devices.
Other articles have followed these new dosing standards as well:
https://pmc.ncbi.nlm.nih.gov/articles/PMC9300948/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10034256/
The Photonic Joules and Einstein dose will now need to be considered in conjunction with all other dosing parameters. Increasing the number of variables that must be juggled for proper dosing protocols.
Conclusions:
Dosing in red light therapy is often considered to be "a riddle wrapped in a mystery inside an enigma" - borrowing words from Winston Churchill in 1939.
It seems some influencers have given up that all these dosing variables are too variable. They would rather abolish dosing parameters all together, and recommend overdosing and excessive heat as their ideal protocol. Turning red light therapy into a heat therapy is a clever way to get people quick relief without needing to understand photochemistry.
In contrast, many PBM researchers are still seeking to make non-thermal PBM a form of precision medicine. They have added more variables as a potential solution to make dosing more universally consistent.
The Photonic Joules and Einstein dose are a first step to start to make more consistent dosing protocols. They have the potential to harmonize the effects of different wavelengths and even combinations of wavelengths.
However, for a consumer to implement Einstein dosing may be challenging. Firstly, the consumer is often not being provided with accurate intensity information and wavelength information. Even when that is accurately provided, it requires a lot of math to account for multiple-wavelength devices.
Much more research will be required to understand the merits and drawbacks of this new dosing system. While it offers great promise, those promises must be thoroughly studied and tested.
For now it is important to understand the basics of this system so we can understand future studies that use it.
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