Image Pop Up

The Difference Between Class III & Class IV Laser Therapy Systems

There are many different laser therapy systems on the market today, each with varying specifications for its power and settings, such as continuous wave, pulsed, and super pulsed. Knowing what will work best for your clinic is complex with all these options and opposing claims.

One significant difference between laser therapy systems is whether they are class III (3) or class IV (4) devices. Knowing the difference and how each will affect the form of treatment you can provide is essential when deciding on a laser therapy system.

Understanding Laser Classification

The FDA classifies lasers based on their potential to cause harm if misused, particularly to the skin and eyes. With misuse, class IIIb and class IV laser devices have the highest potential for injury. Still, even lower classes, such as a class IIIa laser pointer or class II barcode scanner, can cause harm if viewed directly with magnifying optical aids or prolonged exposure to the naked eye.

According to FDA regulations, any laser device class II or above must carry a warning label with the device’s class and power output. A laser pointer toy for cats and a surgical laser for skin ablation have the same labeling policies.

Class IIIb and IV laser devices carry a potential risk of injury when directly viewed and pose a skin hazard. Indirect viewing of class IV lasers can also result in damage. 

As a healthcare provider, you don’t want to hurt your patients, so the idea that a device can put them at risk might be off-putting. However, as with other powerful medical devices like X-rays, CT scans, and MRIs, the benefits greatly outweigh the risks with the proper precautions and training. Any laser therapy device you add to your practice should have comprehensive safety protocols requiring protective eyewear for laser technicians and patients.

What are the Differences Between Class III & Class IV Lasers

So, what’s the difference between class III and class IV lasers? The most significant difference is their maximum power output. The FDA defines a class IIIb laser as a device with a power output between 5-500mW (0.005-0.5W) and a class IV laser as a device with a power output above 500mW (0.5W).

Maximum power output is separate from wavelength so you might find class IIIb and class IV lasers with the same wavelength. Wavelength and power are both critical, but higher powers have a greater penetration depth when it comes to power. A higher-power laser can effectively and safely reach further into the body, allowing a photochemical effect on muscle, bone, and even the brain. Higher powers also reduce the need to press the laser therapy wand into the skin, reducing the risk of bruising.

A less powerful laser can still benefit areas directly beneath the skin and less dense body regions, like the hands and wrists. But high power is necessary to get to and through thicker muscle and bone.

Why Dosage Matters in Laser Therapy

Since laser therapy treats a wide variety of concerns throughout the body, the dosage is more complex. As we’ve already discussed, power significantly influences the depth of penetration of the laser. Another aspect of laser dosage is wavelength. Some standard wavelengths in laser therapy are 635nm, 810nm, and 980nm.

What do the different wavelengths do? The wavelength determines the type of tissue that will respond and produce the photochemical healing effect. For example, light around 635nm is the preferred wavelength for treating skin conditions. Clinical studies will often vary the wavelength, power level, or both when the study aims to find the optimal dosage for a particular body part or a specific concern. One typical result from clinical studies on dosage is that the less optimal wavelength won’t produce any results, or it will produce minimal or placebo results.

Another aspect that makes laser therapy dosage tricky is that each person is unique. Skin tone, body type, and even hair color and type can play a role in determining the effective dosage for laser therapy. How a patient responds to treatment can also call for adjustments.

Additionally, condition-specific aspects can affect the dosage. The size of an injury, the progression of chronic disease, or whether the condition is acute or chronic plays a role in how laser therapy can treat it.

What Laser Therapy System Does My Practice Need?

Unless you only treat specific conditions with laser therapy, a system that allows you to adjust the power output and switch between wavelengths is ideal. It will enable you to treat the widest variety of situations and handle multiple patient types.

If you’re highly specialized, such as a hand surgeon, you might not need a versatile device because most patients will have similar concerns. However, a more generalized practitioner, like a chiropractor, veterinarian, or sports medicine specialist, will want a more comprehensive laser device. They tend to see more patients and must customize their treatment protocols to accommodate them.

When purchasing a laser therapy device, the most important thing is to ensure it is FDA-registered. Devices that are not registered do not have protection in place if the machine malfunctions or the device is improperly labeled, causing harm or failure to produce results. Always make medical device purchases from reputable companies for your and your patient’s safety.


This blog was originally published on December 2, 2019, and was last updated on May 6, 2024.

How Often Should You Do Laser Therapy for Pain?
What Is a Class 4 Laser?