For the purposes of this article we will be discussing Cold Laser Therapy or Low Level Laser Therapy (LLLT), as it is the type of laser commonly used by hands-on healthcare practitioners like Chiropractors, Physiotherapist, Massage Therapists, Veterinarians and many others.

When considering laser equipment for your clinic you should first decide what kind of conditions you plan to treat. Laser devices have different specifications which could determine how well they will perform for the various conditions they are indicated for.

In general, all therapeutic lasers should be evaluated on the basis of how they balance Energy Density and Wavelength. If your laser has the power of your average Christmas bulb, than having the correct wavelength is not a factor since it is unlikely that the photons will reach their target. Conversely a powerful laser using light in the middle of the visible spectrum with will likely have its photons bounce off the surface of the skin. It is the combination of the correct wavelength and sufficient power that will create the therapeutic results through photobiomodulation..

What wavelength should I be looking for?

When it comes to wavelengths, the optimum “therapeutic window” for Laser therapy is from about 650nm to 1000nm. Shorter wavelengths are extremely powerful (X-Rays, Ultraviolet, etc.) and can break the bonds of atoms and produce ions. Wavelengths that are longer than 1500nm are ineffective because water has a very high absorption rate at these wavelengths and since water is a major component of muscle tissue - this radiation doesn’t penetrate much below the skin. Therefore, we are left with a range of wavelengths that are effective for treatment between 650nm and 1500nm where the radiation doesn’t cause any damaging ionization (vs. <650nm) and which are able to penetrate beneath the skin and into the deeper tissues (vs. >1500nm).

Within this range between 650nm and 1500nm, it is the 650nm to 900nm range of wavelengths that is most effective for therapeutic treatment4 5. Wavelengths in the 650nm to 900nm range can penetrate deeper into tissues because the light beam’s photons are not heavily absorbed by the hemoglobin and water in the treatment area tissue, and yet will not produce a lot of unwanted heat like lasers which produce wavelengths over 900nm.

It is widely accepted that longer wavelengths (800nm-900nm) are the optimal treatment range and can penetrate deeper than those at the shorter end of this spectrum (650nm-800nm)4 5. However, it is very important to always remember that output power has a major impact on a laser’s potential depth of penetration. For example, a 2,000mW (2Watt) Laser which produces a 700nm wavelength will actually deliver a faster and deeper treatment than a 200mW (0.2Watt) laser producing a 900nm Wavelength. This is why it is most important when evaluating a Laser or LED device to consider the balance between its wavelength and power.

What is energy density?

“For a given wavelength of light, energy density is the most important factor in determining the tissue reaction” 1Simply put Energy Density is the amount of power your laser actually has per cm2 of treatment area. Without sufficient energy density, you may not be providing any therapy at all as you have not delivered enough energy to the region to trigger a biological response in the tissue. “Research indicates that Energy Densities in the range 0.5 to 4 Joules/cm2 are most effective in triggering a photobiological response in tissue.” 3

Trying to calculate Energy Density sends you down the endless rabbit hole with many manufacturers. The actual formula is:

Laser Output Power (in Watts) x Time (seconds) divided by Beam Area (cm2). This gives you a calculation of Joules/cm2.

The issue is that these are often tough parameters to find out. Manufacturers often list a probe’s total power without specifying the number of diodes or which of these diodes are laser versus SLD or LED (more on that later). In addition with large cluster probes it is virtually impossible to calculate Beam Area for yourself.

The TIME portion can also be difficult to determine. If the device does not offer a Continuous beam mode and instead is always Pulsed or Superpulsed you will need to figure out what percentage of the time the beam is actually on.

Some manufacturers will advertise their Power Density. Power Density is equal to Energy Density IF the laser offers Continuous Mode. Power Density is Output Power divided by Beam Area but this equation does not factor in TIME. The time portion can dramatically reduce the overall number.

For example let’s assume a 5 Watt laser with a Continuous beam and beam area of 1 cm2. The Energy Density (and Power Density) would be 5 x 1 divided by 1 cm2 and therefore equal to 5 Joules/cm2

This same laser Superpulsed would have an Energy Density of only 0.005 J/cm2. Why? Because many of the lasers that can only offer Superpulsed beams use diodes that heat up too quickly. To avoid overheating they Superpulse the beam. This typically means that for each second, the beam is OFF 999/1000 of each second. So in our equation you need to multiply the power by the remaining 0.001 second the beam is actually ON. For this laser Power Density and Energy Density are dramatically different.

Worse yet is that a laser with these specifications is not likely to produce a biological response in the tissue. As per above the ideal range is 0.5 to 4 Joules/cm2. So although you thought you were buying a powerful 5 Watt or a 25 Watt laser your net Energy Density is only 0.005 or 0.025 J/cm2.

Where do you start when selecting a laser?

Personally I start with ANSI (American National Standards Institute). This body has classified all the therapeutic lasers and knows the actual output power of each of their diodes. Technically ANSI is rating the lasers for eye and skin safety but the classifications are limitedly useful for assessing power. Almost all therapeutic lasers in the Canadian market fall into the Classifications of 3B or 4.

ANSI Class IV

Class IV lasers have diodes which output at a minimum of 500 mW (0.5 Watts). As diodes are typically not over 1 cm2, Class IV lasers would always have sufficient Energy Density to generate a biological response.

You will see probes with more than 500 mW that have lower Classifications. This is because they are made up of several diodes, none of which meet the minimum 500 mW individually.

ANSI Class III

Class IIIB is much more problematic. These diodes can range anywhere from 5 mW up to 499 mW. This creates a massive range, so you would need to do much more investigation to determine if the laser is reaching energy densities you are comfortable with.

Treatment Times

Simply put, treatment times are inversely related to the average output power of any laser. All other things being equal, the more output power a laser produces – the faster it can deliver the appropriate dose of energy required to complete a treatment.

Dosage for therapeutic laser is measured in Joules. Therapeutic lasers currently in the Canadian market can deliver as much as 25 Joules per second to as little as 0.025 Joules per second. So for treatments delivering 400 Joules in total, as an example, this represents a vast difference in treatment times from 16 seconds to 16,000 seconds (4 hours and 26 minutes).

Specifications for our devices

Apollo Laser System with 3000mW Cluster Probe

• Emitter Wavelength: 810nm
• Beam Divergence: 9° x 38°
• Total Power Output: 3000mW
• Polarization: Linear
• NOHD: 80cm
• Total Energy delivery per minute: 180 Joules (3 Joules per second), 72 J/cm2 - Treatment Time for 4 J/cm2: 3.51 seconds
• No. of Emitters: 4
• Optical Output Power per emitter: 750mW
• Aperture: 25mm
• Spot Size: 2.7 x 21mm, 0.567cm2
• 1/e2 Power Density (Irradiance): 1.19W/cm2

MedX Laser Complete Console

• Handheld Laser Probe wavelength 808 nm
• 450mW Handheld Laser Probe (3-Diode)
• 2 x 1000mW SLD Cluster heads with 48 diodes each

1. Baxter, G.D. (1994) Therapeutic Lasers: Theory and Practice. Churchill Livingston: Edinburgh (link)

2. Kuru, T. (1198) The Science of Low-Power Laser Therapy. Gordon & Breach Science Publishers, p.xv (link)

3. Mester & Mester, (1989) Wound Healing. Laser Therapy 1: 7-15

4. Anderson, RR, Parrish JA (1981): “The Optics of Human Skin”; The Journal of Investigative Dermatology (link)

5. Zhao ZQ, Fairchild PW (1998): “Dependence of light transmission through human skin on incident beam diameter at different wavelengths” (link)