Aug 24 2012
Low Level Lasers: N-Rays in action.
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31 Responses to “Low Level Lasers: N-Rays in action.”
I see the light!
This was something I could really sink my teeth into.
A truly coherent explanation.
Thanks Mark , Several years ago I suffered a badly broken ankle. The physical therapist associated with Fairfax Hospital tried to convince me a new product would speed bone growth, a laser healing device. I refused explained why it wouldn’t work and asked her to obtain the specs from the manufacturer. I also called the FDA and asked for the study which convinced them to certify the device as medically useful. My request was refused but someone at the hospital concerned about my objections obtained the specs and the trial data.First, of all the red light which was purported to be healing light was not the laser light. The laser frequency was actually in the green. I checked all the absorption ratios for skin tissue and bone etc. against the purported power spec’s and realized it would be completely useless. With this technical information I again quizzed the FDA office and they explained -it was certified because they knew it wouldn’t harm anyone. The clinical trial which was used to approve was not based on tissue studies but on whether the patient felt better or not. A very small sample , about 48% said no and about 52% said yes. The device never was offered to me again and soon disappeared from the PT unit. Moral never offer a phony healing device to a physicist .
From a physicist’s perspective, this makes even less sense than Deepak Chopra’s blitherings – and that’s saying a lot. Classic “sciency” – he’s taken some impressive-sounding terms like ‘soliton’ and thrown them together into a random word salad with no actual meaning.
I’m not generally a commenter. I’m a regular reader, though. I think I’ve read every single article for the last 6 months. You can put me in the “consumer protection” group. I originally discovered this blog when I was searching the infallible Internet for vaccine information when my son was born a year and a half ago. This blog has been a big blessing in my life. You all do great work! I even learn quite a bit from the comments.
For what it’s worth, I’m a Database Admin in a school district in California. My brother, who’s a PA, is about the closest I get to the medical profession. Add me to your data collection to further develop the caricature of your readership.
I think I saw the “based on a theory by Einstein” line a long time ago, possibly in a Johnson Smith catalog, and how ridiculous it was to claim that based on the general laser connection. Of course, anything which involves matter or energy could be described the same way. I’m going to heal your tumor by throwing you off of a building… it’s based on a theory by Isaac Newton!
Scott:
I love the assumption that those electrons will end up in the right place when hurled. I’d like to see the author of that trying to change a set of spark plugs.
ConspicuousCarl- I think that you are unfairly making fun of the Newton cancer cure. I have know of several cases where someone thrown off of a building resulted in halting of tumor growth.
I wonder if the Q1000 really does change its frequency when the setting is changed.That seems like an unnecessary complication of the circuitry that would add to manufacturing costs.A dummy frequency switch would do just fine I think.
Or as comedian Rich Vos (accidentally) put it “Great minds think a lot.”
I really wish the FDA would stop doing that (approving things because they cause no harm, rather than being effective). They are giving these people licences to steal from the unwary, hopeful, or desperate people looking for help. And as Eugenie pointed out even those within the health care field are not immune. I am sure the money spent on that laser could have been spent buying some proven piece of equipment or giving a deserving trained physiotherapist a raise. Every dollar that goes to “Woo” is a dollar stolen from the forms of health care that work.
I too read this blog frequently, but this is the first time I have commented. I practised as a pharmacist 18 years ago, but have since left the profession. My proudest moment was about 11 years ago when I had a “health food” supplement cited by the HPB for false advertising in regards to ADD.
We’re seeing LLLT being touted as a treatment for TMJ issues in the dental field. I have been dubious about its biological plausibility, but haven’t looked into it. Thanks for the article, Mark.
Grant Ritchey
SBM has been one of the sites that I have read nearly every day since I discovered it over a year ago. Today my first thought was to help you with your wondering about the readership. As I read through your blog my next thought was to crawl under a rock and hide for a few days. I am a dentist. It is a great disappointment to see a member of my profession involved in such quackery. Of course, you have Oz and Chopra. As we readers are aware, this stuff is everywhere. I don’t know anything about the dental regulations in Oregon, but if Dr. Lytle were in NC he would most likely be in a very serious discussion with our state board of dental examiners regarding how he might get his license returned. We have this thing about “scope of dental practice” and it is limited to one orifice.
@drfisher,
Don’t be ashamed of your profession because of a few quacks (I know what you meant!) Medicine has much more than Oz and Chopra. We also have Weil and Burzynski. Some of the world’s most famous idiots are MDs. I guess the determining factor is if the profession is inherently based in quackery, like chiropractic, accupuncture, and homeoatphy.
Mark,
Larry Lytle is a known maverick in this field and it is a shame that you should have stumbled upon him before reading the real material.
There are plenty (hundreds) of good RCTs and systematic reviews, and thousands of basic science papers published by reputable institutions including The Lancet, World Health Organisation, BMJ and International Association for the Study of Pain, with over 30 new papers every month being published in peer reviewed journals.
The is good to strong evidence for LLLT on acute and chronic musculoskeletal pain, oral mucositis with limited but encouraging evidence for non healing wounds (venous, diabetic, pressure sores) and neuropathic pain (PHN).
Clinical systematic reviews endorsing Low Level Laser Therapy available here
LANCET http://www.ncbi.nlm.nih.gov/pubmed/19913903
BMJ http://www.ncbi.nlm.nih.gov/pubmed/21708051
BJSM http://www.ncbi.nlm.nih.gov/pubmed/20647296
ESMO http://www.ncbi.nlm.nih.gov/pubmed/22450151
If you want a more plausible mechanism of action then read this from a Harvard Medical School review paper http://www.ncbi.nlm.nih.gov/pubmed/22461763 * there is a link to a free to download paper when you get there
here is a systematic review on the analgesic effects http://www.ncbi.nlm.nih.gov/pubmed/21456946
here is a systematic review on the anti-inflammatory effects http://www.ncbi.nlm.nih.gov/pubmed/16706694
NIH and DARPA have awarded many grants for LLLT research, the ivy league universities (amongst many others) are now contributing papers and Pubmed (NLM actually) have decided on the MeSH term Low Level Laser Therapy (or LLLT for short).
Much effort is going into researching the the effect of LLLT on acute ischemic stroke with a thousand patient study in progress as I type, with TBI and Alzheimer’s looking like promising candidates no far behind.
Please contact me if you would like to discuss this further
* DISCLOSURE I co authored the Harvard paper and own a manufacturing business http://www.thorlaser.com
thorlaser:
I am not a doctor, nor a medical professional, nor a scientist. I’m a software engineer. So a lot of what is in those studies goes over my head; I am not seeing the point. Particularly, I don’t see addressed the question of how laser light can affect these things inside the body, given the very short distance it can penetrate. Indeed, if you wanted to act on things in the blood, wouldn’t it make more sense to stick the laser up your nose (where there is no skin to absorb the light), rather than applying it to the back of the neck as shown on your webpage?
There are a number of very specific claims on your webpage. One of them is that it can act as a temporary nerve block. Having received traditional temporary nerve blocks (anesthetic injections) for various surgical and dental procedures, I’m aware of how potent a nerve block is. Are you seriously saying this can do that? Because if it can, you are missing out on a huge market. Anesthesiologists would love using this; it would be easier and safer and also more popular with patients as most are not big fans of needles. Also, nobody would be allergic to it.
I also have to wonder why coherent light behaves differently than noncoherent light of the same frequency. I don’t have time to read through all of your links to find out if any of the papers explain it, so would you be able to explain it, in layman’s terms? (You don’t have to dumb it down too much; I did take some science coursework at the college level and remain interested in it. It’s just not my area of expertise.)
EM the preceding story & “Moral never offer a phony healing device to a physicist.”
Maybe it’s partly because my dad was a physicist, but I just had to say what a kick I got out of this story. Thanks! MTR
Stephen Barrett from Quackwatch concluded that LLLT was no better than any other form of tissue heating. In other words, LLLT was a fancy, science-y equivalent to putting a hot water bottle on. Perhaps he will change his mind in the face of new evidence. It seems weird to me that so much research has been done on the topic, but it’s apparently not yet widely accepted as safe and effective. Reviews like this and this suggest that perhaps there is resistance and suspicion because they appear to be over-sold.
Obviously it’s complicated, it seems like there would be some applications for surface wounds or features, but I doubt they’re magic and it does seem unlikely that it would have any impact specific to the light or light frequency – but I’m not an expert. I know there are some CAM approaches that involve sticking lasers up your nose (I’m not kidding!) or removing blood to expose it to laser light, then replacing it (also not kidding!) to do…something…and they’re considered rank quackery. Might be why there is skepticism.
I guess that thorlaser wants us to bow for authority, since an ivy league school wrote a positive review. I would like to be shown a single theoretically sound study displaying prior probability.
Mark, I (an engineer) read sbm daily, or skim rather due to the american-specific problems often discussed. Your contributions I never skim, I skip them because it gives me more pleasure to hear you read them as podcasts. This specific topic was an exception though. In my small part of the globe there is a current debate on the medical benfits of cold lasers and I could not wait to see your take on the issue.
Now I think it is time to put down my korean (soon to be illegal) mobile device and strangle a polar bear for lunch.
Lasers are like acupuncture? Actually, lasers sometimes ARE acupuncture (or at least what people claim is acupuncture). Here for example: http://www.ncbi.nlm.nih.gov/pubmed/22888368
From what I remember it doesn’t work much better than needles though, which is to say, of course, it doesn’t.
I’m nothing in the medical field but for an occasional consumer of healthcare, which is why I rarely comment. However, needing health care from time to time… well, this blog taught me a thing or two in deep detail and as a result, I’m looking for a new GP as mine offered me homeopathy twice while claiming that there’s nothing else to be done with hyperhidrosis. (Not sure if botulotoxin injections are that cool as it’s advertised but this one example of something to be done exists. Hey, I’m more informed than my GP.)
Now I’m going back to lurking mode. Hey, SBM folks, continue writing, I’ll check on you frequently.
@Kultakutri
What do you do when your doctor offers you homeopathy? My first thought is to (pardon the language) tell him to go fuck himself. Next is to laugh in his face. Third is to say I’d prefer real medicine. Fourth is to simply walk out of the room. I mean, do you even try to engage in a debate? If they’re a doctor and they’ve stooped that low, does that mean the rest of their practice is also worthless?
Though I use “him”, doctors can be women. In fact, I think they might be moving towards the majority these days…
@ WLU:
I would add to that, report them to the relevant licensing board.
Low Level Laser Therapy (LLLT)
great questions from you all, thanks
“HOW CAN LIGHT AFFECT THESE THINGS”
if you are a doctor or a biochemist you will know mitochondria and cytochrome c oxidase (CCO)
under stress mitochondria make nitric oxide (NO) which inhibits cell respiration reducing ATP and causing oxidative stress
oxidative stress causes inflammation, cell death and cancer
light of the correct wavelength and intensity photo dissociates NO from CCO
oxidative stress stops and the production ATP increases
so the patient gets better.
read this http://www.ncbi.nlm.nih.gov/pubmed/22461763
IF YOU ARE NOT A DOCTOR
I started to write a layman’s explanation but to be honest I don’t have time
but I will explain a few things:
PENETRATION
on a sunny day the paintwork of your car gets hot
but the windshield does not
why ?
paint absorbs electromagnetic radiation (light)
glass windshield does not
but wait …. the windshield will absorb ultraviolet light
that’s why you don’t get so sunburned in a car as you do on the beach
so electromagnetic radiation depending on its wavelength can be absorbed by different materials
there are many chromaphores (light absorbing molecules) in the body
thats why sun light does not pass straight through us
but some parts of the light spectrum passes deeper than others
lasers and LEDs emit one wavelength (ish) and if you choose the right one it goes quite deep
lasers in the range 650nm – 900nm are quite good for penetration (red to near infrared spectrum)
810nm light incident power density of 5W/cm2 on the skin surface achieves approx 5mW/cm2 at 5cm deep which is enough to have photobiological effects.
AND as it happens there is a biomolecule in proteins called cytochrome c oxidase (CCO) that absorbs red and near infrared light
these are iron and copper complexes that are part of one of the most important regulators of cellular energy
at this point you might be wondering are you being fed a bunch of pseudoscience and where is this going ?
no it is not pseudoscience click here
http://www.google.com/search?ie=UTF-8&oe=UTF-8&q=cytochrome%2Bc%2Boxidase%2Bred%2Bnear%2Binfrared%2Blight%2Babsorption
COHERENT LIGHT
not necessary
works with LEDs, does not have to be a coherent laser.
NERVE BLOCK
yes it can and a few anaesthesiologists do love it
yes it is safer
BLOOD
Blood can absorb light, haemoglobin has the coper and iron complex I mentioned above but it is not the main reason for the effect of LLLT on tissue repair, inflammation or analgesia, but it does help the immune system, platelets and volume of blood flow.
QUACKS
this field is full of them screwing up its reputation with their voodoo theories
IVY LEAGUE SCHOOL AUTHORITY
yes I used them a lever for credibility for good reason because when it comes to medicine (don’t ask me about their other schools) they tend to be more systematic and objective than the chiropractors and acupuncturists. (not saying they are all bad, many are very good).
ACUPUNCTURE
whatever acupuncture is it seems to have some effects and lasers seem to work on teh same points but I cant explain it UNLESS you subscribe to the western medical model in which case it is all to do with nerves.
NERVES / PAIN
nerves depend on ATP
LLLT has a does response, at low intensities LLLT makes more ATP
at high intensities it reduces ATP, which in nerve means analgesia.
there is much more to say on this topic but I don’t have time
go to my web site http://thorlaser.com
I got to go now
ZZZ
The journal you cite discusses in vitro results. One of the criticisms ventured above is the failure of light to penetrate the skin. As for the rest of your “mechanism”, this is one of the rare times I would like to see daedalus2u post one of his trademark book-length posts, as he appears to be an expert on NO metabolism.
Wow, you just undermined your argument for everyone on this board. I don’t think any of the editors, and most of the regular readers, believe there is any evidence for acupuncture points being real. This does link to your comment about nerve blocks though – pain is extremely susceptible to placebo effects, and such effects are enhanced by dramatic and sciency-sounding mechanisms. I wonder about the usefulness of lasers in all patients with pain, or is it only effective with a subset? Say…those who respond more strongly to placebo.
Also, you using the words “western model” with and apparent straight face means you lose even more credibility. Last time I checked, science worked in China too.
thorlaser,
Thank you for the answers! I appreciate it, and hope you will stay for some follow-up questions.
* If it doesn’t have to be coherent light, why use lasers at all? Lasers are dangerous to the eyes, after all, and certainly more expensive than a correctly tuned LED.
* You confirm that indeed it is effective as a nerve block. I still find this is a pretty extraordinary claim. You are serious that it can be used to numb an entire appendage? Since these frequencies exist in sunlight, wouldn’t this make us numb on any body surfaces exposed to sunlight? (Not deep inside, just the surfaces.) How much do you trust this as anesthesia? Would you use it for repair of an ingrown toenail, for instance? Or as an alternative to the spinal block preferred for a non-emergency c-section?
Hi, Dr. Crislip,
I’m not a medical professional, just an occasional consumer, but this website, and your contributions may have helped a friend of mine. She saw a 2 1/2 page wrapper ad about laser treatment and since she has no cartilage in her knees, the doctors are recommending knee replacement. She’s been having a lot of pain lately, but doesn’t want surgery. Unfortunately, she lives on Kaua’i and would have to go to Oahu for the laser. I gently tried to steer her away from this quack by pointing out that FDA approval simply means the laser won’t hurt her, but it doesn’t mean it will help her. The “Doctor” is a Chiropractor; I had the nerve to say that he isn’t really a Doctor. I also said her MDs really want to help her, and if this worked, they’d much rather use it than do surgery. And I tried to tell her that the full page of testimonials didn’t include all the people who were not helped by the treatment, and who stopped showing up. First appointment is “only” $17, but this would be a course of treatments, and would end up costing a lot more, plus all the air fare to fly. It was really tough, because she is in a LOT of pain and wants help, but I tried to give her questions to ask if she decides to call about this so-called treatment, because she really can’t afford it, and why spend money for something that’s worthless? I hope it helps her to be more skeptical.
What I’m trying to say is, your writing helps people like me a lot. And that in turn may help others to avoid being victimized by quacks. All of us are medical consumers, and we need help in making good choices. This website is a great source of information, as well as teaching us what questions to ask.
A downside is the increasing size of this website, and the difficulty in accessing relevant information. The search function is good, but there’s no lengthy exploration of specific topics. What I prefer are old-fashioned books, and I read many of the ones that are available about pseudoscience and medical quackery. You could write a wondeful book; with your experience and style, it would be a great read. And while I don’t believe in the healing power of laughter, your sense of humor makes reading and listening fun. Thanks for the posts and podcasts.
Um, no. The body of a car left in the sun gets hot because of what’s under the paint, which has comparatively low emissivity. Chrome will happily get quite hot in the sun, no paint required.
Narad — well, technically, the paint does indeed absorb light. That’s why it has a color. It’s absorbing some frequencies and reflecting others. But you’re right that other opaque surfaces also get hot. Even shiny ones like chrome.
Paint can be used for thermoregulation; it’s why many rockets and spacecraft are painted white, and why American spacesuits are white. (The Russian ones are more khaki in color.) It’s a modest effect, but when cryogenic propellants are so expensive and boil away so quickly, anything you can do to reduce boil-off should be considered. The Space Shuttle’s External Tank was painted white originally; they quickly learned, however, that the mass of the paint completely offset the savings gained by reflecting sunlight in this manner, especially since keeping it cool is really only important prior to ignition. So they never painted it again.
This may be something to consider when car shopping. Light colored cars don’t get hot inside as quickly as dark colored cars do (although on a hot day, even a light colored car can easily reach 150 degrees Fahrenheit).
I’m still hoping thorlaser will come back and answer my followup questions. I’m eager to learn just how effective this is for anesthesia; he never did say if he’d use this for an ingrown toenail removal, or a c-section.
I’m also curious why he is only able to explain why acupuncture works if one subscribes to a “western model”, in which case he says is it all to do with nerves. Perhaps he simply doesn’t realize just how incredibly stupid that sounds, as if he’s glad to make up anything and just wants to know what philosophy to align the mumbo jumbo with.
Superb website…
[...]always a big fan of linking to bloggers that I love but don’t get a lot of link love from[...]……
I understand this. The point was that the paint layer isn’t really the heat sink. It’s going to reradiate thermally to what’s underneath it.
I have been doing other things, so I haven’t seen thorlaser’s reference to NO until now.
The problem with the analysis that thorlaser mentioned is that mitochondria use ROS and NO as control signals to regulate things like ATP level, mitochondria potential and other things that are absolutely essential to mitochondria function.
Yes, light (of certain wavelengths and intensities) does cause the dissociation of NO from cytochrome c oxidase. There was some discussion of that in the context of the magic light helmet to treat Alzheimer’s. I blogged about it.
http://daedalus2u.blogspot.com/2008/06/more-on-magic-light-helmet-for.html
The problem with using light like this is that the effects are dose and dose-rate dependent and non-monotonic. That is what a biphasic dose-response means. When there is a biphasic dose response, you have to be very careful with the dose because if you miss the low-dose therapeutic range, you can get into high-dose toxicity.
Treatment of peripheral tissues with light like this might not have side effects that are too bad. Non-neurons can make ATP with glycolysis if their mitochondria get destroyed. Nerve cells can’t. The problem with dissociating NO from cytochrome c oxidase is that it reduces mitochondria potential and reduces superoxide production. This can be a bad thing, and in the case of non-physiological exposure to light, it is a bad thing. I discuss this mechanism in my blog post.
Because mitochondria use superoxide as a control signal, mitochondria self-regulate to keep the ROS level in the “active range”. If it gets too high mitochondria do things to bring it down. If it gets too low, mitochondria do things to bring it up. As I mention in my post, when the mitochondria potential goes down, mitochondria release cytochrome c and the potential goes back up. The problem with this control mechanism is that cytochrome c is coded for in nuclear DNA. Mitochondria don’t have the capacity to replace cytochrome c once it has been releases into the cytoplasm (there are proteins that quickly deactivate it).
In small cells and in cells that can do glycolysis, that might not be such a bad thing. In neurons it could be catastrophic. Neurons are large cells, with axons extending long distances from the cell body (for example motor neurons can be ~1 meter long). The mitochondria out at the tippy end only get there by being carried out through the axon. It takes a long time for mitochondria to make that trip, and if they run out of something (like cytochrome c) they either get it from the cytoplasm where they are (like O2 and other substrates) or they do without and shut down. Mitochondria can’t do without cytochrome c, once they lose it they are SOL.
Mitochondria can make more ATP, but they have to push the mitochondria potential higher to do so, which generates more ROS. High ATP production rate is always accompanied by high ROS production. If the ROS production is limited by removing cytochrome c, then the ATP production rate is limited too.
I think that exposure to light like this may have no near term adverse symptoms. Physiology has the capacity to respond for a while. Individuals might even feel better due to reduced ROS in the short term. Unfortunately I think this will lead to mitochondria depletion in the medium to long term, months. In Alzheimer’s there might be short term positive effects and then acceleration of decline.
It doesn’t surprise me that researchers have found slowed conduction velocity and reduced action potential magnitude in nerves following LLLT. I don’t know why anyone would think that was a good thing.
The problem with using LLLT like this is what is or should be the dose? That depends on what the mechanism of “therapeutic action” is, what dose, dose-rate provides beneficial effects and what dose and dose-rate produces adverse effects in which tissue compartment(s). If there is mitochondria depletion, then the same dose might start to have adverse effects as the photons per mitochondria increase.
I don’t doubt that people with chronic pain feel less pain after irradiation with light that dissociates NO from cytochrome c in their mitochondria in the nerves that are transmitting signals of pain. What happens to the motor neurons that are close enough to be affected by the same light? Do the mitochondria in their motor neurons get “tired” too?
There may be an increased incidence of ALS in individuals exposed to sunlight.
http://www.ncbi.nlm.nih.gov/pubmed/8154653
There seem to sometimes be excess ALS levels in athletes, farmers and construction workers who spend a lot of time outdoors.
Hmmmm…Interesting.
Drs Huang, Chen, Carroll and Hamblin, from the Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, a Division of Harvard Medical School, concerning the effectiveness of low level laser therapy stated “Since 1967 over 100 phase III, randomized, double-blind, placebo-controlled, clinical trials (RCTs) have been published and supported by over 1,000 laboratory studies investigating the primary mechanisms and the cascade of secondary effects that contribute to a range of local tissue and systemic effects.”
http://www.ncbi.nlm.nih.gov/pmc/articles/pmc2790317/
With all that resource, have you found or read any research that shows these wavelengths of light (red to near infrared) have ANY detrimental effects, such as “mitochondrial depletion” on normal “healthy” tissue? Even at high or prolonged dosages?
Effects of these wavelengths on nerves? I found significant number of studies showing an analgesic effect of these wavelengths of light in patients and animals that have neuromusculoskeletal pain. I also found an article reviewing 44 papers that studied the inhibitory effects of laser irradiation on peripheral mammalian nerves that showed that near infrared laser irradiation “suppressed electrically and noxiously evoked action potentials” However, if you read those articles, you find laser did not suppress the action potentials below the resting potentials of the non-stimulated nerves.
http://www.ncbi.nlm.nih.gov/pubmed/21456946
The reason that is important is that when the average person is told the effects of laser therapy, they automatically think of it “pharmacologically”, like a drug or medication. An anesthetic “numbs” even normal nerves. (like going to the dentist) Light does not. It is analgesic to noxiously stimulated nerves, but has no anesthetic activity in normal nerves (won’t make you numb). This is a different effect than drugs which most often do not discriminate between normal and abnormal tissues. Other biological influences of these wavelengths are similar in that they have physiological effects that lead to healing and decreased pain rather than strictly pharmacological effects. NSAIDs, decreases pain and inflammation, but many slow the healing process. Laser, at the right dosage and wavelength, also decreases pain and inflammation but significantly speeds healing. It does this by lowering inflammatory chemicals, while increasing anti-inflammatory chemicals, and stimulating cellular function, causing faster resolution of inflammation rather than blocking inflammation.
Since sunlight also has UV wavelengths, which has been shown to be damaging, and so many other environmental variables with outdoor occupations, I thought the addition of the 18 year old paper on sun exposure and ALS was an interesting choice to add at the end of his post.
I was unable to find any studies on low level laser that suggested the “mitochondrial depletion” hypothesized by daedalus2U was ever a factor. While it is an interesting hypothesis based on his knowledge of cellular physiology, it does not seem to be well supported by the current literature on this topic, for which there seems to be an abundance.
For those in earlier posts questioning the penetration of these wavelengths, demonstrating the differing tissue penetration effects of various wavelengths of light is fairly easy to do. If you get a red and a green laser pointer, and place the green one on your finger and turn it on, you will see nothing. No penetration (even with the 50 mW one that I have). Then do the same thing with the red one and you will see the red light through your finger. This is an easy way to show the variations of tissue penetration with different wavelenths. How much light, which wavelengths are best, and how to apply it, still needs further study, but with hundreds of studies being published on this topic, and meta-analyses from some of the top medical journals recommending laser for treatment of pain, it is not a topic that is going away anytime soon.