Class 4 laser therapy deconstructed

Wavelength, dose and power – but not heat — are the most important variables affecting the benefits of laser therapy.

So much information on Class 4 laser therapy (or photobiomodulation) is circulating at conferences, in trade journals, and in materials distributed by laser therapy manufacturers, that it is hard to distinguish what the most valuable and relevant data points are.

When considering a Class 4 system, three main variables are most crucial to the beneficial effects of laser therapy: wavelength, dose and power. Note that heat is not one of the variables — we will touch more on that later.

1. Wavelength

A delicate balance exists between wavelength, the absorption of that wavelength by tissue, and the resulting therapeutic effect.1 Melanin, fur, hair, cell fluid and muscle all have different absorption factors of light at different wavelengths. The goal is to find a wavelength that is most effective for the desired target tissue.

The ideal wavelength for skin conditions falls within the 670nm range. For deeper conditions, an 800nm to 900nm range is necessary for ideal penetration to ensure the energy is getting to the target tissue. Specifically, wavelengths around 808 nm have proven penetration through tissue and even bone.2

Figure 1

2. Dose

Just as in pharmaceutical medicine, dose makes a difference in laser therapy. Too little, and there is no impact at all. Too much, and there is risk of causing damage to the cell or tissue (Figure 1).3 The World Association of Laser Therapy (WALT)4 has defined ideal dose parameters to achieve the desired therapeutic effect, and is currently undergoing a rigorous process to update these parameters to reflect current updates in research.

3. Power

The main benefit of higher power is faster dose delivery. Dose is key, and power will impact the speed of that dose’s delivery.

Higher power can also get the dose deeper into tissue as a function of treatment time. However, a major unwanted side effect of higher power is heat, which prevents one from holding a high-power continuous wave laser on one spot long enough to get the dose deeper into the tissue. With many Class 4 high-power therapy lasers, the probe must be moved non-stop to avoid too much heat. This method of treatment is inefficient as energy is lost to the ambient surroundings between the lens and the tissue. Often, a high-power Class 4 laser must be turned down to avoid burning, or treatment must be delivered in contact mode to ensure the energy is reaching the target tissue.

Figure 2

Super pulse vs. continuous wave

One way to get power and penetration without heat is with a super pulse laser.3 A true super pulse laser has a diode with a very high peak power (anywhere from 30W to 200W) and it pulses completely on and off in microseconds (Figure 2) so it never heats up. It is this peak of very high power that increases the penetration into tissue;3 this is very different from pulsed lasers that simply take a 20W laser beam and chop or “pulse” it.

Respond Systems’ Aurora Class 4 Laser Therapy System was engineered based on the above parameters, with safety and results at the core of the design. “We enlisted an expert design team to help build the most effective and user-friendly Class 4 on the market,” says Lisa Miksis, VP at Respond Systems and the Aurora project development leader. “We needed battery backup, portability, stability and durability, all while producing the best results for the patient. The Aurora checks all the boxes without the risk of burning that too much power can create.”

Thanks to the plethora of conditions a therapy laser can treat, it is one of the most beneficial additions to a practice, not only for the patients but also for the financial bottom line. Finding the right one does take a bit of homework, but focusing on the core parameters mentioned in this article will ensure that your therapy laser, whether Class 3b or Class 4, delivers the best experience and results for all.

1Chung H, Dai T, Sharma S, Huang Y, Carroll J, Hamblin M. “The Nuts and Bolts of Low-level Laser (Light) Therapy”. Ann Biomed Eng. 2012 Feb; 40(2): 516–533.

2Anders, Juanita, PhD, USUHS. “The Potential of Light Therapy for Central Nervous System Injury and Disease”. Photomedicine and Laser Surgery. 2009; 27(3): 379-380.

3Samith Ahmed, Gregory Bewsh, Shankaranarayana Bhat, Ramesh Babu. “Low level laser therapy: healing at the speed of light”. Journal of Evolution of Medical and Dental Sciences. 2013 Sept 30; 2(39): 7441-7463.

4World Association of Laser Therapy.


Maria Caiozzo has been a faculty member of the Canine Rehabilitation Institute since 2004. She founded Balanced Canine Products in 2007 and continues to consult and provide high quality rehabilitation equipment to veterinarians, physical therapists and animal owners worldwide. Maria joined the team at Respond Systems, LLC in 2017 as the client growth consultant. Her passion is education and sharing her knowledge of photobiomodulation and pulsed electromagnetic field therapy.