“A Class 3B will take all day to do what a Class IV can do in minutes…”

Peter A. Jenkins, MBA

This claim, used to promote the supposed benefits of a high-power Class IV laser for LPT, is based on the premise that treatment with, say, a 10 W laser takes 6-9 minutes, ergo, with a 500 mW laser the same treatment will take 2-3 hours, which – if you show the maths – is pretty convincing to the lay person. After all, the numbers don’t lie…

Or do they?

This is the logic flow used by the purveyors of high-power lasers:

“Science says you need 6 J/cm2 to treat an osteoarthritic joint, and if you’re treating a hip then you want to cover the whole hip area – about 400 square cm – with a dose of 6 J/cm2, so a total of 2400 J.  

2400 Joules will take 4 minutes with a 10 W laser, but with a 500 mW laser it’ll take 80 minutes to deliver the same dose!  

How much is that extra 76 minutes per treatment worth to you?”

Then they go through a dollars and cents exercise to ‘prove’ that a $30000+ laser is much more cost effective than a $5000 unit. After seeing it presented in such simple terms, it’s hard for an otherwise uninformed prospect to see it any other way.

What many of those who are the targets of – and often converts to – such claims don’t realise is that, as we will shortly see, you do not need thousands of Joules to get the desired outcome.

So, within this context, the numbers certainly do lie.

It’s not the energy produced that counts, but that which is received where it’s needed.

Laser therapy is not about how much energy the laser can generate in a given amount of time, but about delivering an appropriate amount of energy to the target tissues within an appropriate amount of time. If we don’t get the time and energy balance right – whether it’s too little energy delivered over too much time, too much energy delivered over too short a time, or an appropriate amount of energy delivered over too long or too short a time – the outcome will be less than desired. Similarly, not treating the appropriate tissues will also lead to less than optimal (and in some cases, no) results.

We know from high-school physics that energy cannot be created or destroyed; it just changes form. Electrical energy is first converted into light energy within a laser diode, and then that light energy is absorbed within the tissue and converted into heat and chemical energy.

The rate of energy delivery (i.e., the power of the laser beam) to a given volume of tissue, the wavelength of the light and the absorption coefficient of the tissue, and the ability of that tissue to dissipate heat through thermal conduction and radiation, will together determine whether the temperature of the tissue will increase appreciably and, if so, by how much. If the rate of energy delivery and conversion to heat is less than or equal to the rate of dissipation, then the tissue temperature won’t increase.

However, if the rate of energy delivery and conversion exceeds the thermal dissipation rate of the tissue, then the temperature of the irradiated tissue volume will start to increase; the higher the laser power, the faster the rate of energy delivery to the tissue, the faster the tissue will heat up and, ultimately, the hotter it will become.

One way to reduce this effect is to spread the beam over a larger amount of tissue, which is the technique used with high-powered Class IV therapy lasers:  These devices deliver energy at a very high rate, so you have to keep the aperture moving over a large area or you’ll burn the patient.

There are various beam delivery methods employed by Class IV devices, such as an open aperture used with a non-contact scanning technique (e.g., K-Laser, Biolase, Pilot and others), or a rolling ball lens that is placed in contact with the skin (LiteCure – a.k.a. Companion/Pegasus), but whichever method is employed the beam must be kept moving over a large area in order to reduce the potentially detrimental thermal effects.

Constantly moving the beam over a large area, however, means that you really have no control over where that light goes in the tissue, or any accurate knowledge of the amount of light that actually reaches the target tissue. Consequently, a very large amount of energy in total must be delivered over the whole irradiated area to ensure that the target tissue receives at least some amount close to that which is required for effective treatment.

Further confounding the issue is that when you combine this constant motion with a non-contact technique you lose upwards of 50-85% of the incident light through reflection and back-scattering from the skin [1] which means that only 15-50% of the light leaving the laser aperture is actually making it into the tissue where – assuming some of it actually reaches the pathological target – it can do some good.

And, in veterinary practice in particular, if the patient isn’t close-clipped or shaved, the hair, fur or feathers that sit between an open aperture and the skin, or which are compressed between a roller ball and the skin, can absorb, reflect and scatter as much 100% of the laser beam; i.e., NO light is actually reaching the living tissue! Yet we know that light must be absorbed by living tissue for the necessary photochemical effects to take place.

LiteCure, a manufacturer of various high-powered Class IV laser devices for medical and veterinary therapy, acknowledges these losses due to reflection and scattering when using a non-contact method over bare skin but then suggests overcoming them by increasing the power [2]. This is certainly one approach, but, as we’ve just seen, this remedy actually compounds the problem.

And it certainly does nothing to address the problem posed by the loss of light due to hair, fur and feathers:  No matter how much you increase the power, a loss of 100% is still a loss of 100%…

So now we can clearly see why Class IV laser purveyors recommend such high energy doses:  Class IV lasers, when applied as they must be to mitigate the potentially detrimental effects of rapid tissue heating, are extremely inefficient in terms of delivering the right amount of light to the target tissue.

Okay, then, what’s the alternative?

Reduce the power!

It may, at first glance, seem counter-intuitive to suggest that to overcome reflection and backscatter losses one should decrease the power of the laser, but in fact it is backed by very sound reasoning.

A window or lens placed over the aperture and in contact with the skin will more closely match the refractive index of the skin and, therefore, minimise reflection and backscatter, consequently limiting those losses to around 5-10%.

By reducing the power of the laser we can safely place that lens in direct contact with the skin and hold it steady in one place without the risk of burning. And, if we need to cover a larger pathological area, we can use an array of lower-powered laser emitters that combine to produce a higher total power whilst still allowing the stationary contact technique to be used.

In veterinary practice, utilising a lower-powered laser means we can use a smaller aperture – or multiple lower-powered lasers behind multiple smaller apertures – that protrude through the animal’s hair/fur or feathers to contact the skin beaneath, thus ensuring a similar level of efficiency as when treating bare skin with the stationary contact technique mentioned above.

Further, utilising a convex lens over each aperture also affords a number of additional benefits when that skin contact is combined with the application of pressure, all of which serve to maximise the effective depth of penetration of the laser beam in the tissue – particularly important, in addition to the appropriate choice of wavelength, when the pathology is deep-seated:  By applying pressure we compress the tissue and change its optical properties, reducing the lateral scattering of the beam and forcing blood, a major absorber, away from the tissue in the immediate beam path; and, we also decrease the physical distance from the laser source to the target of treatment, thus reducing the volume of tissue within which the beam can be absorbed before reaching the target.

This technique also affords us the ability to deliver energy to the target tissue with greater precision, so less energy is required overall, and gives us greater control over the dose that is ultimately received where it’s needed.

To see a well-researched, practical example of this, let’s consider the treatment of lateral epicondylitis.

The appropriate anatomical targets for this pathology are quite superficial, and readily accessible to both a lower-powered Class 3B device and the scanned beam from a high-powered Class IV device.

LiteCure recommends scanning a 10 W 980 nm laser over the entire circumference of the arm above, below and directly over the elbow joint – a total area of 400–500 cm2 – to deliver a total energy of 3000–4000 Joules at a density of 8–9 J/cm2 [3].

Bjordal et al [4], however, found that the delivery of an appropriate dose to specific individual points was more effective than delivering a similar dose over the entire elbow region, in that irradiating the tendon insertion at the lateral epicondyle, using 2–6 points and doses of 0.25–1.2 Joules per point with a 5–50 mW 904 nm super-pulsed laser, or 6 Joules delivered over a 5 cm2 area with a 10 mW 632.8 nm continuous wave laser, was sufficient to affect significant improvement of pain and function over at least 3—8 weeks.

Comparing these protocols we see that the total amount of energy needed when directly targeting the pathology with a low powered laser is some three orders of magnitude less than that required when using the Class IV laser, which clearly demonstrates that less is more when it comes to determining efficacy in laser therapy.

And although the output powers of the 5-50 mW 904 nm and 10 mW 632.8 nm lasers are around one one-thousandth that of the 10 W device, the treatment times in this example are very similar, ranging from 5–6.5 minutes for the Class IV laser to 1–10 minutes for the lower power devices.

Most Class 3B lasers used today have output powers in the 50–500 mW range and, even though when using a laser at the upper end of this range one may need to slightly increase the dose per point to affect a similar outcome, it is easy to see that using the more precise and targeted approach afforded by a Class 3B device will save a significant amount of time per patient.

To summarise, using a high-powered Class IV laser to treat large amounts of tissue that don’t contribute to the overall outcome is simply wasting time and money!  Further, because significantly more energy is being delivered to the tissue so quickly, Class IV lasers may have unintended negative effects and pose a greater risk to the patient and the practitioner.

In stark contrast, the accuracy and precision of treatment afforded by a well-designed Class 3B laser ensures excellent outcomes at a significant cost saving – both in terms of time spent treating patients and in the initial price of the equipment – and a significant reduction in the risk of injury.

Placing a lower-powered laser probe in contact with the skin, holding it stationary over the pathology, and applying pressure when the pathology is deep-seated, is the only way to accurately and precisely deliver the required amount of light to the target tissue.

The numbers, in this latter case, don’t lie.



1.  Al Watban FAH (1996) Therapeutic lasers effectiveness and dosimetry. Biomedical Optical Instrumentation and Laser-Assisted Biotechnology, NATO ASI Series E Applied Sciences, Vol 325, 171-183

2.  Reigel, R J (2008) Laser Therapy in the Companion Animal Practice. Mechanisms and Protocols for Class IV Laser Therapy. LiteCure, LLC.

3.  Reigel & Pryor (2008) Clinical Overview and Applications of Class IV Therapy Lasers. p14.

4.  Bjordal JM, Lopes-Martins RA, Joensen J et al. (2008) A systematic review with procedural assessments and meta-analysis of Low Level Laser Therapy in lateral elbow tendinopathy (tennis elbow). BMC Musculoskelet Disord. 9:75