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Class 3b vs Class 4 laser

I currently operate a 200Mw 820nm single diode head (or a 200MW LED cluster) - Omega Laser - which appears effective in a wide range of presentations. However several vets in my area have decided to invest in Class IV lasers and clients are clearly impressed; there are reports of very quick analgesic effects. So I am wondering whether I need to consider this modality to preserve parity of practice. The vets are just lasering away on a wide range of preset protocols, but in my view, EPAs are better supported with manual therapy and relevant exercise prescription contemporaneously - which the vets are not able to offer.

I have seen a class IV laser (MLS laser by Celtic SMR Ltd) in use on dogs; in one case reasonably effective for analgesia on elbow dysplasia - tx resulting in altered/improved gait; but in another dog with HD there was a strong objection to tx ( not clear whether the adverse response was to increased tissue heat or worry of a timid dog from the audible beeps but I had to hold it and I was pretty uncomfortable with the degree of restraint needed)

Obviously the competing manufacturers' literature is disparaging of the alternative. I wonder if there is any thorough work on the penetration depths achievable (I have not found any) or whether any forum contributors can offer anecdotal thoughts about efficacy of class 4 vs class 3b Thank you for any input Helen

Helen Tompkins

3 months ago

Back to General Electrotherapy

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Prof Tim Watson
Prof Tim Watson

Found this paper (De Marchi, T., et al. (2017). "Phototherapy for Improvement of Performance and Exercise Recovery: Comparison of 3 Commercially Available Devices." J Athl Train 52(5): 429-438) which might throw some additional useful light on the discussion. Using RCT design, does NOT show that high power is 'better' in a DOMS / healthy human participant study

Jessica Nelson, Omega Laser Systems
Jessica Nelson, Omega Laser Systems

The research overwhelmingly supports the fact that wavelength (nm) is the main parameter determining penetration with the early 800nm range being the best. There is conflicting evidence as to whether ‘’super pulsing’’ can offer better penetration but what is not supported by research are claims by Class 4 (IV in USA) companies and their reps that higher powers offer significantly better penetration despite the fact the rely almost totally on the positive research carried out using the 3B lasers. It is possible the Class 4 lasers will work if they supply the correct parameter re wavelength (nm) and energy (J)/energy density (J/cm2) but this paramter is unclear as they are delivered at a distance with loss of power through reflection and scattering, a large spot size and a scanning action to prevent heating. Research supports the requirement for relatively low doses for healing (15 – 20 secs per point with a 200mW) while higher doses result in inhibition (40 – 60 seconds) which is useful for analgesia but is not appropriate for tendon injuries. Some of the Class 4 companies claim a back calculation of energy at depth requires high doses on the surface of the skin which ignores all the published clinical evidence they rely on. Some vets have been drawn into this by believing the hype and repeating claims of better penetration on their websites, something that I am glad to say is appearing less and less as they are being challenged. As a Class 3B manufacturer for over 25 years you may consider me biased but if this is to be evidence based practice then follow the research. For an independent opinion and references from an expert in the field of laser research read and/or and see also

Prof Tim Watson
Prof Tim Watson

There have been a LOT of e mails coming through over the last few weeks on this topic and I am encouraging people of access and join in with this discussion (whether related to animal or human based therapy)

At the end of the day, there are a lot of claims that Class 4 lasers are 'better' than the more commonly employed Class 3(b) units. They apparently (a) deliver more energy and (b) the light goes deeper into the tissues.

Delivering more energy (or the same energy in less time) I can see - though I am not sure I can see the clinical advantage other than reducing the treatment time - which is not especially long in any case. We have substantial evidence re the amount of energy needed for clinical efficacy - does not say that this is dependent on which type of laser is used to deliver - it says how much energy (or energy density or fluence or . . . .) is needed

As for the increased penetration, I struggle with this one. We know that laser penetration (the % of light reaching tissue depth X) depends on several things - wavelength being one of them. If using light of wavelength YY nm penetrates into the tissue such that ZZ% of that light reaches 1cm depth, then this does not change by increasing the power of the laser - surely?? The same % reaches the 1cm depth. The actual amount of energy will be different, but the % remains the same - though I stand to be corrected by those who know laser better than I do

IF there is a clinical advantage (I know about the cell studies & animal/tissue models) than I would just love to know about them - as would many readers and users of this Forum - please contribute


Some thoughts that I use in my clinical thinking that might help in this matter.

  • Class 3b low power laser (up to 500mW), has the common name of "cold LASER", and those of class 4, high energy, "hot LASER". Class 3b LASERs are also considered as biomodelators and class 4 as surgical, "lithic".
  • the therapeutic vector (dose) of LASER is the energy (joules) administered
  • the effect of LASER is achieved on the tissues that absorb the applied energy. More absorption plus therapeutic effect.
  • A high energy LASER can administer low doses.
  • The wavelength also seems to be associated with the depth of treatment, the higher the more it is absorbed. The high power Co2 (10,600 nm) LASER is easily absorbed just to the surface (skin), and therefore destroys it. Corrections please.


Interesting links:

Last updated 3 months ago


Hi Helen I've worked with a LLLT before in dogs and horses. Since 5 years I've been working with different class IV'. I feel a big difference in results compared to the LLLT. You mention a heating problem treating hips , especially in the MLS this is not the case because MLS is not heating up the tissues. That's one of the main reasons why I decided to buy the MLS While testing Companion and K-laser I experienced burning wounds. I was even able to put a piece of paper on fire within 45sec. The main problem in the Laser-hype is that anyone is buying laser devices, without any background on laser or physiotherapy. The same for the companies selling them. They mention different frequencies, powers, wavelenghts, the bigger the better, without real scientific figures. At this moment all on treatments is based on case studies with no blind controls. From my experience as a veterinarian and animal physiotherapist I'm happy with the MLS device compared to the other two


Hello Helen, Have you seen this website I hope is helpful

Eva Physiotherapist

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