I just read through this thread with interest… (I had not seen it before). I am somewhat familiar with some of the physical therapy uses for IR. So I decided to get some LEDs to experiment with.
I found these XP-E Far Red (720-740nm) LEDs at Rapid LED:
mounted on 20mm boards and on sale. They also have some 660nm and 720-740nm now in XP-E2.
true
there is also research with 620nm and even 530nm (green) has been shown to have benefits
670 just happens to be available inexpensively in 5mm LEDs that the study this thread started with, refers to
it is by no means required that we use just 670nm… there is a considerably wider range of biologically active LED frequencies.
It is also not necessary that we use a single focused Laser frequency
there are studies that tested a blend of 580 to 620nm that also produced therapeutic results…
basically, the energy coming from an LED does have biological effects, and is not in any way limited specifically to 670nm
google is our friend, its not hard to find studies that use many other frequencies than 670nm
just yesterday I researched using LED light for migraine, and one of the first hits was green light. I had to exclude green, to dig up the red light application I posted above in post #248, that used a combination of:
“super pulsed laser 905 nm; infrared 875 nm; Red 670 nm”
I gave my daughter a 660nm XP-E2 light, she used it as posted above in #248, and a couple hours later she smiled and said, “btw, my headache is gone”
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I have installed XP-E2 660nm and also XP-E2 730nm LEDs in some AAA lights, discussed here and in several posts on the following page from there.
the cliff notes is, my AAA lights lose their modes with XP-E2 Red 660 and 730nm, while AA lights seem to retain them with 660 and 730nm, but 730nm is very very dim
Im presently researching the XP-G3 660nm because there is a report that the XP-G3 645nm retains mode spacing in an AAA mod
I presently use a 730nm XP-E2 in an AA light, sometims at 1 lumen, and occasionally at 5 lumens
and I use 660nm in an AAA light, at 5-7 lumens, and it relieves arthritis and muscle pain for me, just like 730nm does
Ive also been using those lights on my eyes, and lately Im finding I often take my glasses off, and seem to see better than usual, without them…
Im really glad I found this discussion, I had no prior Red Light Therapy experience, and Im finding it very useful
Thanks Jon for your contributions to this subject. I have some single mode buck drivers I will use and tune the output around 350-500mA range with sense resistor. See what it will do, I have suitable hosts.
Off subject; I love that part of NM where you live! From Santa Fe to Taos, Georgia O’keeffe country. Some of the most beautiful landscape I have ever experienced. Enjoy.
Im indeed extremly fortunate to live here and experience the beauty. I went up to the aspens near the ski area today, with visiting family, including a new grandson. Extremely happy times. Despite corona, wearing masks, and using social distance, it was total soulfood for me to see them here.
I like your single mode red light plan
my opinion is that 5 lumens of 660 nm is plenty
and imo 1 lumen of 730nm is also effective, while 5 lumens of 730nm is imo more intense than necessary, when using the light in direct contact with my body.
for those interested in evidence that other frequencies besides 670nm are biologically active, here is one example of a different opinion:
660nm works better than any other frequency
and from the same link:
“Your mitochondria can absorb red light easily at the 630nm and 660nm wavelengths”
and here is a table of red light therapy products and their wavelengths… you will see biological claims all the way down to 405nm
there is an inexpensive 660 nm red light coming available… recommended
sofirn C01R
not affiliated, just a fan
Sofirn will also make a C01 with a 5mm 670nm red led. It is not available for preorder yet.
https://sofirnlight.com/c01-aaa-flashlight-5mm-3400k-led-95-cri-p0152.html
670nm beam might look weird.
If the final version still has this issue, you can probably fix it with d-c-fix diffusion film.
I will get one to compare, but I do not believe that there is much difference between a rated 660nm red led and a rated 670nm red led for the purposes of this thread.
thanks for your thoughts, and for taking the time to share links
I agree 10nm is not a significant difference
I prefer the 3 modes of the C01R 660nm
the C01 670nm uses a 5mm LED and has only one mode
there is no lens, so cant use dcfix
to hide artifacts in the beam, we can use sandpaper on the LED
Im not a fan
Progressive Myopia or Hyperopia Can Be Induced in Chicks and Reversed by Manipulation of the Chromaticity of Ambient Light
https://iovs.arvojournals.org/article.aspx?articleid=2127682
Results.: Red light induced progressive myopia (mean refraction ± SD at 28 days, −2.83 ± 0.25 diopters [D]). Progressive hyperopia was induced by blue light (mean refraction at 28 days, +4.55 ± 0.21 D). The difference in refraction between the groups was highly significant at P < 0.001. Induced myopia or hyperopia was axial as confirmed by ultrasound biometry. Myopia induced by 21 days of red light (−2.21 ± 0.21 D) was reversed to hyperopia (+2.50 ± 0.29 D) by subsequent 21 days of blue light. Hyperopia induced by 21 days of blue light (+4.21 ± 0.19 D) was reversed to myopia (−1.23 ± 0.12 D) by 21 days of red light.
Conclusions.: Rearing chicks in red light caused progressive myopia, while rearing in blue light caused progressive hyperopia. Light-induced myopia or hyperopia in chicks can be reversed to hyperopia or myopia, respectively, by an alteration in the chromaticity of ambient light. Manipulation of chromaticity may be applicable to the management of human childhood myopia.
Good catch to find that interesting article from Dec 2013, i can only wish that red light could reverse my hyperopia (far-sightedness) to where i could see clearly again.
I see, myopia from exposure to Krypton’s red sun as a baby must be the reason why that journalist, Clark Kent, wears glasses. 
I guess I must be from Krypton too, given my myopia, but so far I can’t fly. 
Given all the blue light exposure we have nobody would have myopia if it had a strong effect on humans.
IIRC myopia may actually be correlated to lack of UV exposure as a children, so similar effect but the wrong wavelength on humans.
Edit: Other research says that myopia may be correlated to low brightness rather than low UV exposure, Why Outdoor Time Matters in Myopia Development - Myopia Profile , I’m not sure how reliable is that source.
People promoting alternative treatment saying that conventional treatment makes things worse in the long term, their information may be somewhat biased.
I didn’t know that clouds have fine details rather than just being white blobs until I got glasses, if someone had shown me a detailed photograph of a cloud before, I would have say that clouds don’t look that way, so I definitely had myopia before, but my myopia is slight (around –2.0 or –2.5), I could get out by foot without glasses if I wanted, only I would have trouble reading signs until I’m close. I don’t know if I ever will do the surgery because it may be not worth (for me).
I just learned that some colorblind people are a lot less sensitive to photo red. I wonder if anyone here has that issue and does not know about it. I wonder if that means that far red light, which most of us can still see, is completely invisible.
My test subject basically couldn’t even see the deeper shades of red. Like using some red emitters and adjusting the brightness showed he was 25x less sensitive to photo red than I was. So that much-lauded R9 number is basically worthless to the red-green colorblind. (The other types are so rare to not be worth considering.)
If they have reduced red perception they may be able to see other colors but I would expect that far red would be too faint.
If they just lack the L cones that discriminate between green and red they won’t be able to see it at all or at least have big issues seeing it. If you trust the Wikipedia graph, M cone sensitivity pretty much goes to 0 at 660nm and beyond.
OTOH IIRC someone (you?) in this thread have said that they can tell apart 660nm and 730nm by color. The cones can’t detect wavelength directly, the color perception comes from the difference between each cone signal. If the signal from the M cones is already at zero you shouldn’t be able to tell the two wavelength apart, unless you have 4 types of cones (the extra cone is between M and L cones). Of course it could just be ambient light messing with the color perception.
I can see that my XP-E2 Far Red 730nm flashlight looks slightly less orange on a neutral background than SST-20-DR 660nm.
The dominant wavelength for a 660nm led is probably about 645nm. Since these leds are not pure emitters of just 660nm or 730nm wavelength of light, I am probably just seeing orange because of the portion of emitted light that is below (for example) 640nm.
it was 620 and 660
further up this page I also posted 660 and 730, but the difference is not as obvious in a photo. They still look different side by side (the 660 is more orange than the 730). Plus 730 is like 100x less visible (less bright).
However, even if we cant see it, 730, 810, 900nm all have therapeutic value,
so do 620 and 660nm, and those are easy to see.
so for light therapy, being color blind is not an obstacle
AFAIK we don’t know whether therapeutic value (if there is any beyond placebo) is affected by color blindness. We would need a study for that.
the mechanism of charging mitochondria is not dependent on being able to see the light
and the mechanism of using a red light to relieve arthritis and migraine pain, has nothing to do with being able to see the light. It works even with eyes closed 
Have yall been seeing TV ads for the laser hair-growth caps—one site indicates they are using red @ ~650nm.
don’t know if these are just red leds or actually laser diodes, but they aren’t budget items.
capillus website: “Capillus laser therapy devices use only medical grade laser diodes as a light source. ”
Hi guys,
Would this red light be sufficient for the red light eye therapy?