Deconstructing Red Light Therapy Intensity: Why MORE Isn’t Always BETTER!

Red Light Therapy Intensity: Why Higher Power Isn’t Always Better for Results

“High intensity, medical grade Red Light Therapy”. This is a statement that is often made about Red Light Therapy devices, implying that to see real therapeutic benefits, that a device must be really powerful. But is this actually true? What does the scientific evidence say about high intensity Red Light Therapy devices?  Let’s dig into the research.

But first, we need to define what light “intensity” is. Light intensity (also known as power density) describes the amount of light being delivered by a device. Also sometimes called irradiance, it’s usually measured in units called mW/cm². Intensity is related to power, which is the rate at which energy is delivered, measured in Watts (W). If we look at that energy per square cm of exposure site, we get W/cm², or mW/cm² – our intensity. So, intensity is the amount of energy from a device at any given moment, and if we consider that as a function of time of exposure, we get the energy density (measured in J/cm²), which is the total energy delivered over time. This combination of intensity with exposure time is also referred to as the “dose” of light delivered by the treatment. 

Let’s dig into the assumption that higher powered devices are required to derive benefit by exploring five lines of evidence.

1. Where did the idea that high intensity Red Light Therapy is required for therapeutic benefit come from? This idea comes from the fact that for decades, virtually all research and applications of photobiomodulation were done with lasers, which are high intensity devices. Research into Red Light Therapy began in the 1960’s, and lasers dominated the field until around the early 2000’s, when LED’s (light emitting diodes) began to be studied. The scientific literature is comprised of around 85% studies using lasers as light sources, with the rest using LED’s. Companies making higher powered devices are often trying to get close to the power of lasers, citing laser research that shows benefits. However, hundreds of studies have now shown that LED Red Light Therapy yields many benefits, such as reducing pain and inflammation. And, LED’s have four important advantages over lasers: (1) they’re safer, (2) they’re cheaper, (3) they can be easily used at home, and (4) LED’s can cover a greater area of the body allowing more tissue to receive light. Given this, an important question for researchers in the field to address was whether the benefits of Red Light Therapy were specific to something about laser light, or whether those benefits could be replicated using LED’s. In 2018, an analysis that reviewed the comparative evidence of lasers versus LED’s concluded that “most of these comparisons provisionally suggest that lasers could indeed be replaced with LED’s without significant worsening of the results.” This is despite majordifferences in power outputs, which demonstrates that high intensity lasers are not required for therapeutic benefits.
   

2. Does the research on Red Light Therapy demonstrate that a certain intensity range is needed to observe therapeutic benefits? There is an excellent comprehensive database online of published photobiomodulation research studies that describes the details of thousands of Red Light Therapy studies. We can look at this database to compare the intensity (power) of studies relative to their results, and to see if there are clear trends, such as a requirement for high intensity/power to yield benefits. Most studies using LED’s have an intensity between 10 and 100mW/cm² and are most commonly between 10 and 50mW/cm². For lasers, the intensity is much higher, based on the different characteristics of the light produced. Positive results spanning a wide range of outcomes are observed, and there are no clear trends related to light intensity. Some studies use extremely low intensity LED lights, some use higher intensity LED lights, and some use high intensity lasers. Although studies of certain light intensities are sometimes used to support specific products, when you look at the totality of the research, the main conclusion that can be drawn is that exposure to red and/or near infrared light across a wide range of light characteristics, including intensity, yields biological benefits.
   

3. Can devices with different intensities be used to deliver the same “dose” of light?  Theoretically, the time variable can be manipulated when using devices with different intensities to deliver the same “dose” of light. Mathematical calculations show that higher intensity devices used for shorter periods of time can deliver a comparable dose of light to lower intensity devices used for longer periods of time. However, some research has demonstrated that our bodies don’t seem to absorb photons the same way when they are delivered at a high intensity, suggesting that “dose” may not simply be a mathematical calculation of intensity and time. For example, a recent comprehensive review of studies of red light therapy for the brain found that “NIR [near infrared light] light with low-power density (15–30 mW/cm²) is a more effective intervention than that with high-power density (40–90 mW/cm²).”
   

4. If low, moderate, and high intensity devices have been shown to deliver therapeutic benefits, are there reasons for preferring low or moderate intensity rather than high? Yes, there are reasons to prefer low to moderate intensity devices as compared to high. For example, high intensity light can increase oxidative stress, which is harmful to biological health. When wounds are treated with low/moderate intensity red light therapy, markers of oxidative stress initially increase and then decrease dramatically as healing progresses. However, when wounds are treated with high intensity red light therapy, oxidative stress remains high. Similarly, levels of antioxidant enzyme activity (which reduces oxidative stress) increase with low/moderate intensity red light therapy but not with high intensity light. This suggests that low/moderate intensity Red Light Therapy reduces oxidative stress, while high intensity Red Light Therapy may cause it to increase. High intensity light also carries a risk of heating tissues and causing thermal damage. 
   

5. Are there biological reasons to expect that there could be an upper limit to Red Light Therapy intensity when it comes to therapeutic benefits? Yes! Researchers have carefully studied the biological effects of Red Light Therapy and have clearly concluded that “dose” matters. If the dose is too low, there is no benefit; similarly, if it is too high, there is also no benefit – and there is the potential for harm. This is called a biphasic dose response, also known as the Arndt Shulz law. Picture this as an inverted U curve. If the dose is too low or too high, there will be minimal response, but there is a relatively wide range of doses in the middle range that are beneficial. As described by Dr. Michael Hamblin, “It has been consistently found that when the dose of [Red Light Therapy] is increased a maximum response is reached at some value, and if the dose in increased beyond that maximal value, the response diminishes, disappears and it is even possible that negative or inhibitory effects are produced at very high fluences.” Because “dose” is a function of intensity and time, using high intensity devices for too long can easily yield a dose of light that will not be beneficial, and may even be harmful. 
   

These five lines of evidence clearly illustrate that the assumption that high intensity devices are needed to achieve benefit is not accurate. It is the dose that creates the benefit – and dose is a function of intensity and time. While it may be appealing to use a higher intensity light to get the treatment done faster, this carries risks including thermal damage due to heating tissues, as well as a risk of causing oxidative stress.  The tendency when using a high intensity device – which would require a treatment time of only a few minutes (or even less) – is to overdo it. For at-home devices, low to moderate intensities leave more wiggle room in terms of both safety and benefits. 

Fringe Red Light Therapy Intensity

Fringe Red Light Therapy products were designed to deliver light at an intensity of 20-40mW/cm2, which is the approximate intensity of the sun. This has been described as the “sweet spot” between higher intensities, which can have harmful effects, and lower intensities, which will have no effect at all. Although there are no clear distinctions between low, moderate, and high intensity devices, the intensity of Fringe Red Light Therapy devices would most appropriately be termed as low/moderate and stands in contrast to many devices on the market, which are 100mW/cm2 or even higher. At this intensity, our products can safely be used for treatment periods between 10 and 30 minutes, and our products are programmed with built-in timers to deliver a safe and effective dose of light. 

We verify the intensity of our products using third party testing, which is important because independent research has found that many commercial home-based Red Light Therapy products do not deliver light as advertised. 

Take Home Points

• The idea that high intensity Red Light Therapy devices are needed for therapeutic benefits originated from decades of research using high intensity lasers; however, subsequent research has demonstrated that lower intensity LED powered devices can yield comparable results.
• An analysis of the totality of published Red Light Therapy research (using both lasers and LED’s) shows that benefits can be seen when using devices that span a very wide range of intensity, from low to high.
• This is consistent with research that shows the effective “dose” of Red Light Therapy follows a U-shaped curve, with benefits spanning a wide range but which has a lower and upper limit.
• The “dose” of light is determined by its intensity and the treatment time, although research has shown that delivering light quickly using a high intensity device may not be as effective as delivering it more slowly using a lower intensity device, suggesting that the “dose” is not the only factor that determines benefits.
• High intensity light can increase oxidative stress and the risk of thermal damage, so care must be taken when using high powered devices to limit treatment times, which can be difficult to do when using at-home devices.
  

The Verdict? Research evidence does not support the claim that high intensity Red Light Therapy devices are required for therapeutic benefits. Using low to moderate intensity devices yields results that are comparable to using high intensity devices, with some research even demonstrating greater efficacy. Low to moderate intensity devices also have the advantage of greater safety.  py, and it can be safely used at home as part of a regular wellness regime. Choose a device that suits your needs and preferred treatment conditions, and which delivers both red and near infrared light at an appropriate intensity. Combine red light therapy with an anti-inflammatory diet and supplements, regular exercise, stress management, and good sleep hygiene for best results.

Dr. Genevieve Newton, DC, PhD  spent close to 20 years as a researcher and educator in the field of nutritional sciences before joining Fringe as its Scientific Director. Gen’s job is to “bring the science” that supports Fringe’s products and education. She is passionate about all things Fringe, and is a deep believer in healing body, mind and spirit using the gifts of the natural world. 

The contents in this blog; such as text, content, graphics are intended for educational purposes only. The Content is not intended to substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your healthcare provider.

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