I assume you had a cut-n-paste failure with that link. I think you meant https://www.frontiersin.org/journals/neurology/articles/10.3..., which I assume you picked because the title. It is an interesting article, should you ever decide to read it beyond cherry picking the caption from 'Figure 2'. But TL;DR: It doesn't say what you apparently think it says. The author is questioning the therapeutic value of low power infrared light therapy, and demonstrating what is required for medical effect. He is not questioning whether or not infrared light can penetrate skin and bone, because it does. For example:
We have demonstrated that our multi-watt NIR data delivers an estimated 1.65–3.7 J/cm2 to a depth of 30 mm. As shown above, this is within the biologically meaningful fluence range (1, 2, 4, 6, 47) and is more than 100-fold greater than the fluence delivered by an LED system or by a low-power infrared light system according to the findings of the authors cited above (7, 18, 21, 37, 38, 48).
and
Patients receiving 10–20 treatments of multi-watt infrared light, each lasting approximately 20–30 min, have experienced significant, and often, dramatic improvements (47, 48). The fluence of combined 810 and 980 nm light delivered during each of these treatments was, on average, 81 J/cm2/treatment. Correcting for forehead skin, skull, and 1 cm of brain tissue, this delivered a fluence of fluence of 0.41 J/cm2 to the neurons 1 cm below the cortical surface.
NIR in the power range of 10–15 W at 810 and 980 nm can provide fluence within the range shown to be biologically beneficial at 3 cm depth. You can't ELI5 more than that.
Understanding does take work, and given your posting history of mostly low effort negative snark, I probably spent more time than I should have. But it was an interesting diversion into something I otherwise wouldn't have known.
Now, the skin of the forehead overlying a portion of the frontal lobes is approximately 2 mm thick. It is possible that tiny amounts of infrared light from lower powered emitters could penetrate the forehead skin; however, only 9–11% of the light from a 10 W emitter penetrated that thickness of skin. Nevertheless, the remainder of the scalp, over which hoods, helmets, and posteriorly placed LED pads are emitting low-power light, is an average of 5.1–5.8 mm thick.
Simply put, it does not matter how long an LED is shone on a human head if the light energy from that LED cannot penetrate through human skin further than 3 mm. The energy of low-power devices simply will not penetrate the thickness of the scalp overlying much of the skull.
Some have suggested that NIR energy from low-power devices penetrates deeper if longer exposure times are used. This reflects a fundamental misunderstanding of the roles that scatter, absorption, and refraction play in degrading NIR energy as it passes through tissue.
The energy delivered to the skin surface is different from the energy that penetrates to the depth of the target tissue – often several cm below the surface.
Longer exposure times will simply pump more energy into the epidermis and dermis of the skin/scalp.
Longer exposure times do not yield deeper penetration. These limitations on penetration only take into consideration the skin and scalp; however, the skull is a formidable barrier to light penetration, as well.
This is all moot however, as NIR is not light, because people can't see it (and possibly no animals can). If you drop the frequency enough something will get through (a tiny percent) and if you keep calling it light then you can make the false claim that light passes through bone, when we know that isn't true because we can see bones and they aren't transparent. We could say radio waves pass though people too and therefore light goes right though people.
however, only 9–11% of the light from a 10 W emitter penetrated that thickness of skin.
Yes. The study discusses this. Its why the researchers moved to more powerful sources. To provide the results you refuse to read. Which I explicitly pointed out in my reply so you didn't have to worry about struggling with reading comprehension yourself. Which you ignored because it doesn't fit your narrative.
it does not matter how long an LED is shone on a human head
Yes, that is what the researchers said. LEDs don't have enough power; they measured that. That's why they didn't use regular LEDs. And they measured that change. And gave you the parameters of their setup for you to check (well, not you...for people into facts and science and such). And cited the people who had similar results. And cited people who had different results. And other science things that people who actually read this stuff for comprehension appreciate. That you ignore.
The energy delivered to the skin surface is different from the energy that penetrates to the depth of the target tissue
Different...energy? Physics would like a word with you. But physics does expect you to have done your homework, so I'll let it know you won't be around any time soon. I told it to be nice, and remember not everyone has a high school level understanding of physics, and they might say silly things. Be excellent to each other and all that.
often several cm below the surface.
Yeah. How about 3cm? Like the researchers said. In their measurements. That they didn't guess at.
the skull is a formidable barrier to light penetration, as well
Yes. The researchers discuss skulls in detail. Not just people skulls...sheep skulls and mice skulls too. 3cm on people; all the way through in mice. Sheep somewhere between. And a lot about hands, but I don't figure you care about those. They wrote it down and it got published. After actually doing the science.
This is all moot however, as NIR is not light
There it is! Ding ding! The audience watching at home knew this was coming.
If it was 'moot', you would have said "Acksually, infrared ain't light so STFU. Duh!" a couple of exchanges back and moved on to easier targets with less annoying 'facts' and 'proof' and 'published works of science by experts' around for anyone who cared to check. I guess even the most seasoned troll gets to a point where their own contrived protests become too silly to keep up with a straight face, and the lazy out is to not just move the goalposts, it's to move them to a different stadium.
Go forth and declare your victory, brave internet warrior. You have outlasted my ability to whip between WTF and LOL and Kagi is telling me "dude, you can't out-research aggressive ignorance". Besides, there's a hockey game on and my wife made cocktails.
If it was 'moot', you would have said "Acksually, infrared ain't light so STFU. Duh!"
I did mention this in my first reply, I don't know why you feel the need for this manic response.
I guess even the most seasoned troll gets to a point where their own contrived protests become too silly to keep up with a straight face, and the lazy out is to not just move the goalposts, it's to move them to a different stadium. Go forth and declare your victory, brave internet warrior. You have outlasted my ability to whip between WTF and LOL and Kagi is telling me "dude, you can't out-research aggressive ignorance". Besides, there's a hockey game on and my wife made cocktails.
I don't understand where these insults are coming from. It doesn't seem like you're addressing that lower frequency EM that no animal can see isn't light. Saying "WTF and LOL" and trying to be patronizing doesn't confront what I posted.
You realize for most of your post you are replying to your own source right? I didn't write that, I took it from your link and put the most relevant stuff in italics. When you are quoting "Simply put" and replying: "The siren cry of ignorance everywhere." that's from your link, not me.
We have demonstrated that our multi-watt NIR data delivers an estimated 1.65–3.7 J/cm2 to a depth of 30 mm. As shown above, this is within the biologically meaningful fluence range (1, 2, 4, 6, 47) and is more than 100-fold greater than the fluence delivered by an LED system or by a low-power infrared light system according to the findings of the authors cited above (7, 18, 21, 37, 38, 48).
and
Patients receiving 10–20 treatments of multi-watt infrared light, each lasting approximately 20–30 min, have experienced significant, and often, dramatic improvements (47, 48). The fluence of combined 810 and 980 nm light delivered during each of these treatments was, on average, 81 J/cm2/treatment. Correcting for forehead skin, skull, and 1 cm of brain tissue, this delivered a fluence of fluence of 0.41 J/cm2 to the neurons 1 cm below the cortical surface.
The authors paper listed as citation #4 (https://www.tandfonline.com/doi/full/10.2147/NDT.S78182#medi...) has more detail on his methods, and the abstract sums it up pretty well:
NIR in the power range of 10–15 W at 810 and 980 nm can provide fluence within the range shown to be biologically beneficial at 3 cm depth. You can't ELI5 more than that.
Understanding does take work, and given your posting history of mostly low effort negative snark, I probably spent more time than I should have. But it was an interesting diversion into something I otherwise wouldn't have known.