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A 2017 study by researchers from the UK found that visible red wavelengths — including 610, 630, 650, and 670 nm red light — can absorb into the skin to a maximum depth of between 4 and 5 mm.

Another finding was that NIR light (810, 830, and 850 nm) can absorb into the tissue to a maximum depth somewhat greater than 5 mm, or a little over 2 inches. 

This absorption depth extends to the bone, muscle, blood vessels, organs, abdominal fat, lymph nodes, and other tissue and fluids well beneath the skin.

Studies have shown that NIR wavelengths ranging from 700 to 750 nm have limited biochemical activity and are therefore not often used. More research is needed; but in the meantime, light between 630–660 nm and 810–850 nm appears to have the most profound benefits; that is the “therapeutic window” mentioned previously.

Beyond 1,000 nm, the story changes. Infrared saunas often use wavelengths longer than 1,000 nm as part of infrared light therapy — although this is another area where caution is advised due to the possibility of thermal damage.

Above 1,000 nm, the body begins to perceive the wavelengths as heat, not light. This is important for anyone treating their eyes, or trying to boost testosterone levels, because certain parts of the body, particularly the eyes and the testicles, are incredibly sensitive to thermal damage.

NIR light in the low 800 nm range generates negligible amounts of heat. This could make the treatment suitable (and safe) for applications in which far-infrared light could cause cell damage.

Keep in mind that these absorption depths for red and NIR light therapy are only general guidelines and refer to optimal conditions. The absorption depth of light photons can be influenced by the length of the treatment, any skincare products on the skin (which can block light), light-blockers such as hair or clothing, and the power of the LED light therapy device.

The Benefits of Red Wavelengths 

The most beneficial red light wavelength for skin is commonly considered to be 660 nm, which is near the upper range of visible red light. This wavelength has deeper penetration than the shorter 630 nm wavelength, with similar effects.

Red wavelengths penetrate the skin and sebaceous glands to rejuvenate the skin’s tone and texture. The 630 and 660 nm wavelengths are the two most widely studied wavelengths of the red light spectrum. Here is a small sampling of some of the powerful benefits:

• Reduced fine lines and wrinkles: In this study, the 630 nm red light wavelength was combined with other beauty treatments (e.g., microneedling) to create a statistically significant improvement in photodamage, fine lines, and sagging. This finding has been supported by numerous other clinical trials, such as a 2014 study by researchers from Germany. 
• Improvement in chronic skin disorders like psoriasis: One study showed that the use of the 630 nm red light wavelength in conjunction with hematoporphyrin derivative (HPD) helped to eliminate the symptoms associated with psoriasis within 17 days.
• Hair regrowth: According to a 2013 study, red light therapy containing the 630 nm wavelength is a safe and effective method of stimulating hair growth in both men and women.
• Treatment of acne: A 2017 review published in Dermatology Times states that red light therapy could be a viable treatment for acne. Many popular LED light treatments for acne combine blue and red light.
• Reduced training fatigue: A 2011 study revealed that red light at 660 nm combined with 830 nm NIR light can delay the development of fatigue in the muscles, and enhance skeletal muscle performance. This is one of many studies that suggest using more than one wavelength together could have profound benefits.
• Reduced inflammation: In a study investigating the effects of red light therapy on pleurisy in rats, the 660 nm wavelength was found to induce an anti-inflammatory effect. 
• Improved bone healing: A 2015 study found that red light at 660 nm was even more effective than the 830 nm wavelength in increasing ATP production in vitro and an initial acceleration of callus formation in the bone fracture healing process.
• Reduced neuropathic pain: A 2014 study investigating sciatic nerve pain in rats found that the red 660 nm wavelength significantly helped to reduce pain.
• Accelerated wound healing: In 2013, researchers conducting this study found that the red 660 nm wavelength increased the formation of new blood vessels and enhanced collagen deposition to help in the healing of wounds. 

On their own, the 630 nm and 660 nm red light wavelengths are highly beneficial. But you will get the best results by combining shorter and longer wavelengths in the visible and invisible light spectrum.

The Benefits of Near-Infrared Light Wavelengths

The “best” NIR wavelengths for deep-tissue treatment are typically believed to be 810 to 850 nm, which is near the upper range of NIR light. Here is a small sampling of the findings of various studies and clinical trials on the effects of the most widely studied wavelengths ranging from 810 to 850 nm.

An especially exciting discovery of several studies is near-infrared light’s promise in enhancing brain health — including treatment of brain disorders and recovery from brain injuries.

The 810 nm wavelength offers a unique array of neurological benefits. Many forward-thinking scientists share the belief that NIR light therapy will become a prominent medical treatment for brain disorders in the very near future. 

• Improved recovery from stroke in certain patients: One study conducted with stroke patients showed that 810 nm NIR light wavelengths provided neuroprotective benefits and improved recovery among sufferers of moderate to severe strokes. Five days after the stroke, there was significant improvement among those who had been treated with 810 nm light therapy, compared to those who had not. Ninety days post-stroke, 70 percent of the treated patients had a successful outcome, compared with only 51 percent of the control group.
• Improved recovery from traumatic brain injury: As confirmed by this pilot study in 2007, 810 nm NIR light therapy has been shown in animal models to be particularly effective in promoting recovery from traumatic brain injuries and reducing long-term neurological damage.
• Interest in the ability of near-infrared light to support improvement in psychiatric disorders goes as far back as this 2009 pilot study co-authored by world-renowned red light therapy expert Michael Hamblin. Prescription drugs have long been recognized as having a limited ability to assist individuals suffering from psychiatric conditions, and often come with a host of unwanted side effects. In this study, 810 nm NIR light applied to the forehead was shown to help patients suffering from major depression and anxiety, with no adverse side effects.
• A 2018 review of several studies confirmed the neuroprotective effect of near-infrared light on the brain.

Other benefits of NIR wavelengths include:

• Improved healing and recovery: A 2017 study of soccer players showed that the 810 nm wavelength applied before activity enhanced muscular performance and post-exercise recovery.
• Accelerated wound healing: This 2014 study found that 810 nm wavelengths helped expedite wound healing in diabetic rats, which enabled the tissue to granulate more rapidly. A study from 2013 suggests that the 830 nm wavelength accelerates healing in wounds and helps to ward off infection. In this small study, which involved five patients with various types of wounds, all five of them experienced wound healing, controlled infection, and lessened discomfort during treatment periods ranging from one to eight weeks (depending on the severity of the wound).
• Improved outcomes following plastic surgery: During a 2015 study, South Korean researchers found that swift exposure to 830 nm wavelengths after aesthetic surgery hastens recovery, reduces downtime, and enhances the results of surgery by reducing swelling, infection, bruising, and pain.  
• Improved bone repair and growth: A 2008 study by researchers from Brazil demonstrated that 830 nm light therapy improved bone repair by stimulating new bone growth. 
• Faster return-to-play after injury: The ability to return to play as swiftly as possible after injury or trauma is a key concern for any amateur or professional athlete. This 2016 study confirmed that 830 nm NIR  light therapy significantly and safely reduced the wait time before injured athletes could return to play. Over a 15-month period, 395 injuries were treated with 830 nm light therapy, including sprains, strains, ligament damage, tendonitis, and contusions. The study authors found that the treatment successfully brought about accelerated healing in all wounds at different stages, and successfully controlled secondary infection.
• Enhanced muscle recovery after a hard workout: A 2016 study co-authored by Hamblin observed the use of 850 nm wavelengths on athletes and found that the use of NIR light increased muscle mass after training and decreased inflammation and oxidative stress in muscle biopsies.
• Orthodontics and tooth alignment: A clinical trial published in 2016 confirms that using the 850 nm wavelength supported faster realignment of teeth for patients undergoing orthodontics. 

As valuable as these results are, it bears repeating that better results could be expected by combining wavelengths in the red and NIR spectrum. Let’s explore that now.

Then What Really Is THE Best Wavelength and Spectrum for Red Light Therapy?

Ultimately, this comes down to one question: Which wavelength will give you the results you want?

The short answer is that you will get the best results by using multiple red (610–660 nm) and near-infrared (820–850 nm) wavelengths simultaneously. By combining multiple wavelengths of red and NIR light, you will experience superior results. 

The Therapeutic Spectrum: Harnessing the Power of Five Wavelengths

Let’s start with the red wavelengths. If you use 630 nm light along with 660 nm light, the shorter 630 nm wavelengths will, of course, have a shallower absorption depth. 

As the light photons pass through these layers to reach their maximum absorption depths, they travel together, increasing the effect on the tissue that is within the range of both wavelengths.

As they move through the tissue, both wavelengths will work together up to about 4 mm. After that, the 630 nm wavelengths are extinguished while the 660 nm wavelengths continue into slightly greater absorption depth before extinguishing.

This two-wavelength combination will help reduce the loss of energy that occurs as light photons pass through the body — and when you add longer wavelengths to the mix, you exponentially increase the number of light photons interacting with your cells.

If you shine five wavelengths (630 nm, 660 nm, 810 nm, 830 nm, and 850 nm) on the target treatment area simultaneously, something incredible happens: the longer wavelengths amplify the effects of the shorter wavelengths.

As the light photons enter the skin, all five wavelengths interact with the tissues they pass through. It’s very “bright” in the irradiated area, and this five-wavelength combination has a significant impact on the cells in the treatment area.

Some of the light photons scatter and change direction, creating a “net” effect in the treatment area in which all wavelengths are active. This net effect receives the light energy of five different wavelengths.

The net will also be bigger when you use a larger light therapy device; but for now, we’ll stay focused on how the individual light photons behave in the body.

The following illustration, from a 2017 study by UK researchers previously referenced, shows how light penetrates deep into the body’s tissues. This helps you visualize how the scattering effect works: