LED phototherapy, or Red Light Therapy, is a powerful and versatile treatment modality with a broad range of applications. It’s a deeply transformative tool that taps into the body’s metabolic systems, triggering a cascade of biological effects that can significantly enhance skin health, reduce inflammation, and promote cellular rejuvenation.
However, to unlock its full potential, it's crucial to understand the foundational principles. My aim with this blog post is to provide a straightforward, easy-to-follow guide that you can refer back to whenever needed and it not be overwhelming with jargon. The biological effects of light therapy are vast and complex, but for this post, I’m keeping it practical. Think of it as your "LED Phototherapy for Dummies" guide.
Once you understand the basics of how light interacts with the skin, you’ll be able to use this powerful tool more effectively in your practice—whether you're a dermatologist, aesthetician, wellness professional or an at home enthusiast.
The Challenge of LED Therapy
Let's get one thing straight. In an ideal scenario, if you were to isolate cells and irradiate them, almost any light would have an effect. The problem is, the body’s layers of skin and tissue stand in the way. So, while we know light affects cells, the challenge comes with getting it deep enough into the skin to reach the mitochondria — the powerhouse of your cells — where the real therapeutic benefits happen.
To navigate this, we need to consider how light travels through the skin. This means looking at both the wavelength of light and the intensity at which it’s delivered. Understanding these factors helps you ensure enough energy is absorbed by the cells, avoiding issues like absorption by melanin or scattering, and instead focusing the light where it can be most effective.
Let’s break it down….
1. The Relationship Between Irradiance (Light Intensity) and Wavelength
Light behaves as both a particle and a wave, and the wavelength of light plays a crucial role in how deep it penetrates the skin. The greater the wavelength, the deeper the light can travel.
Shorter wavelengths, such as blue light (400-500nm), mainly affect the surface layers of the skin. They tend to be absorbed by melanin, which is concentrated in the epidermis, and they don’t penetrate past the outer skin layer. This makes them great for treating surface-level issues, like acne or bacterial infections, but less effective for deeper concerns.
On the other hand, red light (620-680nm) can penetrate into the dermis. This wavelength stimulates collagen and elastin production, making it an excellent choice for promoting healing and improving skin texture.
Then there’s Near Infrared (NIR) light, ranging from 750 to 1200nm, which penetrates even deeper. NIR light is ideal for targeting deeper tissues, reducing inflammation, and addressing musculoskeletal issues like joint pain.
But here’s the thing: intensity matters just as much as wavelength. The irradiance, or intensity, of light determines how deeply it can penetrate and how much energy the cells absorb. Higher irradiance means the light will have a greater force to reach deeper layers, but it also means the cells will absorb more energy, which can trigger a stronger biological response. However, it’s a balance; too much intensity can push the body beyond its optimal response, so finding the right level is key.
2. Absorption
The way light interacts with the skin depends on its wavelength and the chromophores — the light-absorbing components within the skin. Melanin, water, hemoglobin, and oxyhemoglobin are the primary chromophores that absorb light. Each of these has a specific absorption spectrum, meaning they absorb light most effectively at particular wavelengths.
For example, blue and red light are absorbed predominantly by melanin in the epidermis, which is why people with darker skin tones may have different responses to these wavelengths. Near Infrared (NIR), however, is absorbed more by hemoglobin in the blood, which means it’s great for improving circulation and reducing inflammation in deeper tissues. Longer wavelengths above 1100nm are mostly absorbed by water, which is abundant throughout the skin and deeper tissues.
By selecting the right wavelength, you can avoid excessive absorption by these chromophores, ensuring that more of the light’s energy is absorbed by the cells and tissues where you need it most.
3. The Journey of Light: How it Travels Through the Skin
When light hits the skin, it doesn’t just go straight to the target cells. Some of it is reflected off the surface. The rest travels deeper through the layers of skin, but how deeply it penetrates depends on the wavelength.
Shorter wavelengths, like blue light, travel at a higher frequency meaning there are more frequent interactions with particles in the skin, which leads to more reflection and scattering. This means they primarily stay in the upper layers of the skin. The longer the wavelength is, the less frequently it will have these interactions, which allows the light to penetrate deeper.
However, there’s a catch. While longer wavelengths can reach deeper layers, they also carry less energy. This means they need higher irradiance to make sure the cells still absorb enough energy to trigger the desired response. It’s a balance of depth versus energy, and understanding this helps you fine-tune the treatment for optimal results.
4. Dosing: Finding the Right Balance
LED phototherapy follows a biphasic dose-response curve. This means there’s a minimum threshold of energy required to trigger a response. If the energy is too low or not delivered within the right timeframe, no response.
As intensity increases, the biological response will rise to a theoretical optimal point. After this optimal dose, the effectiveness starts to diminish. That doesn’t mean the treatment becomes ineffective. It just means that beyond a certain threshold, the body doesn’t respond as effectively. Even so, positive effects still occur. At the time of writing, there are no studies or literature indicating negative effects from overdosing on light therapy. But determining the optimal dose is tricky. It depends on many variables that influence how the light interacts with the body, including skin type, skin condition, age, collagen volume, hydration, and the thickness of the skin at the treatment site.
Here are some basic principles I personally consider when determining a good dose:
Thicker skin areas (like the back) may require higher irradiance to ensure effective penetration.
Collagen volume decreases with age, so older individuals might need lower irradiance levels to achieve optimal results.
Darker skin types contain more melanin in the basal layer, which can impact light penetration and increase thermal sensitivity, potentially leading to hyperpigmentation, especially with lower wavelengths of light.
Compromised skin barriers may struggle with the increased blood flow triggered by red wavelengths. In such cases, limiting red light and focusing more on NIR (Near Infrared) light can be more beneficial.
While these are general guidelines, the exact dose will always depend on the unique characteristics of the individual and their skin and the more the practitioner understands how the light will interact with the skin the more optimal the dose delivery can be.
The LED Therapy Cheat Sheet for Skin Conditions:
Now that you’ve got the basics down, here’s a quick reference for how to approach different skin conditions with LED therapy:
Eczema, Rosacea, Psoriasis: Start with NIR to reduce inflammation and calm the skin. Once inflammation is controlled, introduce red light gradually to support skin barrier function.
Acne/Bacterial Issues: Blue light is great for its antibacterial properties, but it can slow mitochondrial function. Transition to NIR once the surface issues clear up to promote deeper healing.
Anti-Aging: Stick with red and NIR light. Avoid blue light, as it may slow down mitochondrial function, which is essential for rejuvenating the skin.
Deeper Conditions (e.g., Joint Pain, muscle issues): NIR light is your go-to for reducing inflammation in deeper tissues.
Wound Healing: Tailor your approach to the stage of healing. Industry experts like Dr. George Christopoulos and Kate Moneith-Ross offer great insights on this. LED phototherapy can be an incredibly effective treatment, whether used alone or as a complement to other therapies. By understanding the basic principles of how light interacts with skin, you can optimise your treatment approach for better outcomes.
Final Thoughts
LED phototherapy is a remarkable tool that can be used on its own or alongside other treatments for powerful, visible results. But understanding how light interacts with the skin is critical to optimising its effects. By knowing how to adjust parameters like wavelength, irradiance, and dosing, you’ll be better equipped to use this technology effectively, whether you’re treating acne, promoting anti-aging, or addressing deeper conditions.
I hope this guide serves as a practical reference for both professionals and home users alike, helping you maximise the benefits of LED phototherapy.
References:
Gajinov, Z., Matić, M., Prćić, S., & Đuran, V. (2011). "Optical properties of the human skin." Acta Medica Medianae, 50(2), 29-34.
Anderson, R. R., & Parrish, J. A. (1981). "The optics of human skin." Journal of Investigative Dermatology, 77(1), 13-19.
Liu, Y., & Zeng, Y. (2012). "Clinical applications of red and near infrared light for photobiomodulation therapy."
Baranoski, G. V. G. (2009). "An Introduction to Light Interaction with Human Skin." Springer Science & Business Media.