#1

Studies claiming benefits of red, near-infrared (NIR), and IR light use 20 to 200 mW/cm². A factor of 10, yet those selling rediculously overpriced devices recommend times below 15 min, not 150 or 1.5 min, and because of “biphasic dose response”, i.e. long exposure is detrimental due to cell heating (you don’t say), ROS, and/or NO release (thought that was the whole point?). They measure 6 to 8 inches from the source, proudly lecturing us on the inverse square law, which holds for point sources, like single LEDs, not for the flat panels they sell. And don’t you dare rely on the watts rating of a bulb since that may all just be heat! Never mind that IR is literally … “heat radiation”. BTW, white light has more red and more heat than redish heat radiation. I use heat radiation because it gives much red at relatively little heat. I want a sauna, not an oven.

My sauna has red heat lamps spreading at most 550 W over ~ 4m² about a meter away, that is 14 mW/cm², and I turn by 90 degrees every 15 min or so over an hour. Seems to be too little, too careful?

Feel free to use ChatGPT, our new scientific standard replacing critical thinking, to tell me how recklessly stupid I am because, for example, I do not know the power at exactly 620nm, 630nm, 633nm, 660nm, 670nm, 808nm, 810nm, 830nm, 850nm, 1064nm, … a small selection of advertised most crucial wave lengths for ideal results such as photodissociation of nitric oxide from the copper enzyme cytochrome c oxidase in mitochondria, or penetration in order to reach any mitochondria below the skin in the first place.

BTW, the bulbs are dirt cheap from China, without having been first imported by a reputable non evil entity to change the label and resell, so I will succumb to SARScancer any day now. Before that, anybody having some constructive criticism? (I won’t buy spectrometry devices. Tried methylene blue an hour before, not sure yet if it is placebo, but certainly does not feel bad.)

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#2

Admittedly I’m not entirely sure after reading your post what it is exactly that you are asking. But the amount of exposure mW/cm2, potential ROS induction, etc. has been discussed in some threads.

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#3

The Inverse Square Law is your friend… and does apply to flat panels, which are made up of “points” of radiation. While many points will help in delivering more power over distance than 1 point, there is still loss over distance.

While not flat, even a contiguous light source like the sun loses power over distance. Even the coherent energy from lasers in space lose power over distance, and not just from “dust” interference. Distance is not our friend when comes to benefit OR it is our friend when it comes to harmful types of radiation.

All “radiation” loses power based on the distance, and it can be a significant loss. This is one of my pet peeves when I see people using a red light 2 or 3 feet away from their skin and they hilariously think they are getting a benefit :slight_smile:

It takes power to penetrate skin and it is specific as to how deep a particular wavelength can penetrate at a given power level. Our skin is an excellent filter and barricade, keeping out all the bad chit :slight_smile:

As you mentioned the fundamental of the inverse square law is based on a point source but the real question is, how big can a point be :slight_smile:

Since many red light devices do have a visible spectrum and some with an invisible spectrum one could purchase a meter (optical) or 2 (IR) or 3 (UV) and take some measurements.

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#4

Yes. All light diverges from its source.

#5

You forgot about lasers! :slight_smile:

Not to mention that the numbers they announce are totally over inflated. I did a teardown of a 45W panel here and it was only 0.58mW/cm2 at 27.5".

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#6

Lasers too. No matter how parallel as it leaves the source, a laser beam diverges with distance.

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#7

What utter nonsense! It is plain geometry.
d-dimensional sources in D-dim space distribute over a [D - (d+1)] dim hypersurface, whether a five-brane in 10 D string space or a 2d flat panel in 3D space. So the radial distance goes in with the power of 3 - (2+1), which is Zero!

#8

This is not true. The inverse square law does not apply to flat panels. The law comes from the fact that a point light distributes evenly in all directions in three dimentional space, in which case the inverse square law predicts how much of the light will hit a target at a certain distance. The law does not apply to red/NIR light panel because for such panels the light does snot distribute evenly in all directions. The panel has mirrors that direct the light mostly, although not completely, in the forward direction, similar as the light coming from a flash light. This means that you will see a decrease in light hitting a target at double the distance but not nearly as much of a decrease as if you would if the light came from a point source. Think of a flash light. If you point a flas light at someone from a 1 meter distance and he moves further away so he is now 2 meters away the strength of the light on him is decreased by a good bit but nowhere close to as much as if the light source were a standard round light bulb instead of a flash light.

Not if it travels in a vaccuum.

It’s totally reasonable to get benefit at that distance. You would just need something around 20 minutes of exposure instead of 5 minutes at the much shorter recommended distances. This can be practical if you only have a small panel but need to treat a large area and have extra time for longer exposure.

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#9

I think a “point” source size is relative with respect to distance if it’s not coherent.

I’d agree on the laser in a vacuum point, but again the source power is going to diminish over distance, delivering less power at the target, here on earth.

But we’re not using lasers, that was just a talking point :slight_smile:

LEDs are point sources, panels are made of many point sources that are diverging.

Power (and wavelength) enables depth penetration, not time. If there is not enough power from an LED delivered at a specific distance to penetrate the skin is that beneficial? Just because people see the red glow on their skin does not mean they are getting a benefit. Benefit requires penetration.

Those power/wavelength/depth measurements are fairly well established in human skin so would be easy to test.

In another life, we used to sell this company a lot of laser diodes and used their meters for QC.

#10

Like I said earlier, they are diverging a lot less because of the mirrors that direct the light mostly in the forward direction. It’s very obvious to people that own red/NIR light panels that this results in a lot smaller reduction in power with distance than light from a point source does when not directed.

You will get penetration at longer distances, the dose will just be that much lower. Penetration is not time dependent.

Anyways if we stay on topic, my main point is, people can absolutely use red/NIR light panel at a much greater distance than the recommended distances. I have used my panel several times at a three feet distance and it results in the same short-term pain reduction from an injury as it does when I use it much closer as long as I keep the exposure time several times longer.

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#11

Absolutely, you make up for increased distance by increasing exposure time.
There is no need for panels to be 3" from the body.

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#12

Only if the power delivered is not diminished by distance. And the only way to know that is to measure it at the surface of the skin, not the rated power of the light source.

For LED light to penetrate the skin to a clinically useful level, most devices operate with a power output between 40mW/cm² and 100mW/cm²; however, the ideal power depends on the wavelength of light used, with red and near-infrared light generally considered the most effective for deep penetration, and the specific treatment goal.

Key points to remember:

  • Wavelength matters:

Red and near-infrared light (wavelengths around 630nm to 950nm) are generally preferred for deeper skin penetration.

  • Power density is key:

Power is measured in milliwatts per square centimeter (mW/cm²) and is crucial for determining the depth of penetration.

  • Clinical considerations:

Different treatment goals might require varying power levels and treatment durations.

Here is a red light vendor that understands the importance of the vartiables, i.e. power, wavelength, distance and has a nice chart on power delivered over distance. NOTE: they use the same meters we used to use

A Thorlabs S121C optical power sensor.

Screenshot 2025-01-23 at 12-45-27 Complete guide to light therapy dosing - Red Light Man
Screenshot 2025-01-23 at 12-45-27 Complete guide to light therapy dosing - Red Light Man786×599 16.5 KB

Note that at 10cm/4" distance the power has dropped significantly at the surface of the skin.

#13

The power from any point source other than a laser will be significantly diminished by the distances we are talking about.

#14

I’m scrolling through this modern day equivalent to the “how many angels can dance on top of a pin head” disputation while doing a methylene blue infused facial half a foot or so away from my red + IR light panel. All I know is I got a 30 degree beam angle that’s the narrowest they have, for more cohesive reflection. And I trust my own skin and subjective wellbeing as a gauge of the U-curve’s sweet spot on exposure time. Too much overthinking on this thread.

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#15

image
image1920×1440 133 KB

I’m THIS close.

#16

That is the power output to get a clinically useful level with a short treatment time (a few minutes). You can get a clinically useful dose with a much lower power density (by being further away from the panel) by increasing the treatment duration.

This is misleading. Power does not determine skin penetration depth at all. It determines the dose. A lower power will penetrate as deep as a higher power light, it will just need a longer duration of exposure to reach the same dose.

All this talk about power being so important only applies if you want to get the desired dose delivered in a typical short time (less than 5 minutes). It doesn’t mean you can’t use lowe power and get the same dose and penetration just by using longer exposure times. It’s just not discussed as an option because not many bother to do a 20-30 minute exposure time. But there are even studies that use very low power for such long duration and they get the same effects as higher power for shorter duration.

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#17

I am not sure there is a massive disagreement here. The only real question is if a minimum power is needed for some reason or just the total energy matters (per cm sq). I think it is energy, but there may be a power threshold. In any event when i use panels i reduce distance to reduce time required.

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#18

This piqued my curiosity so I started looking for more info on the “dosing” as I’ve been focused on delivered “power”.

Sometimes I’m blinded by the numbers :wink:

https://www.aao.org/eye-health/news/red-light-protect-aging-eyes-rlt-pbm-near-infrared
https://academic.oup.com/biomedgerontology/article/75/9/e49/5863431?login=false

The above study, while small is what got me doing RLT in 2020.

To better understand “dose”, my search was “clinical study on Red light therapy dosing” And you have forced me to accept that, as in all things, dose matters, including PBM. Due to variances in PBM devices, the methodology is a more complex dosing process than taking supplements :slight_smile:

I have been doing RLT for 4 years but not consistently, when I have been consistent, I have not noticed much difference in anything. That is probably why I’m inconsistent with this compared to other things where I get positive feedback.

I found this site with a lot of good info and clinical references. There is a LOT of variance and still a lot of questions on “dose” in many of the studies referenced.

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#19

Paper referenced in article. Speaks to mechanism. Dosing remains a mystery for LED based devices due to complications in measuring output and absorption from devices with many LEDs.

“Photobiomodulation therapy (PBMT), also known as low-level light therapy (LLLT), has attracted widespread attention in treating KOA (knee arthritis) because it is drug-free, non-invasive, safe and useful with rarely reported side effects. It provides the biological stimulatory effects primarily by enhancing the activity of mitochondrial cytochrome c oxidase. This stimulation, in turn, fosters cell proliferation and tissue regeneration”

The mechanisms of PBMT are not totally uncovered so far. Ample experimental evidence suggests that cytochrome c oxidase (CCO), the key enzyme in mitochondrial respiratory chain, acts as the acceptor of photons (Karu, 1999; Hanna et al., 2021). And the light absorption later results in increased production of adenosine triphosphate (ATP), release of nitric oxide (NO), induction of transcription factors and modulation of reactive oxygen species (ROS) (Karu, 2008; Kim et al., 2017). Apart from this, PBMT also displays its therapeutic effects through regulating angiogenesis, modulating blood flow and stimulating the expression of inflammatory factors (Zhang and Qu, 2023).

the biphasic dose-response of PBMT, a phenomenon characterized by lower doses exerting stimulatory effects and higher doses display inhibitory or even detrimental effects (Chung et al., 2012; Nie et al., 2023), also needs to be taken into consideration when investigating the optimal light parameters.

the irradiation location also matters. Feng et al. (2023) suggested the optimal irradiation location was on both sides of the patella, where the largest dose of PBMT could reach the articular cartilage.

PBMT can effectively lead to pain amelioration partially because its cardinal functions in resolving synovitis and reducing inflammatory factors releasing, but it can relieve pain through inhibiting central sensitization as well.

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