Penetration of Light Energy

Research and clinical studies show that when NIR light energy has sufficient power density, it is capable of penetrating biological tissue and bone to produce therapeutic outcomes without negative side effects.

What is NIR light energy?

Near infrared light (NIR) energy is part of the electromagnetic spectrum – which are waves (or photons) of the electromagnetic field.It radiates through space and carries electromagnetic radiant energy. Several existing technologies depend on the ability of electromagnetic energy to penetrate solid objects, such as WiFi, mobile data, radar and navigation satellites.

Figure 1 The electromagnetic spectrum

The depth or the power of penetration by light energy depends on the wavelength in the electromagnetic spectrum. Thus, the longer the wavelength, the greater the ability for photons to penetrate an object. NIR light energy is found around the center of the electromagnetic spectrum.

Why near infrared light energy for brain photobiomodulation?

The near infrared (NIR) window is the range in the electromagnetic spectrum where light has a maximum depth of penetration in tissue.^[1] This is because the NIR window is defined by the absorption of photons by blood at the shorter wavelengths and by water at the longer wavelengths. NIR light energy also derives the greatest mitochondrial response out of the entire electromagnetic spectrum.

Figure 2 The near infrared window or body’s optical window. Image source: Wang, Erica & Kaur, Ramanjot & Fierro, Manuel & Austin, Evan & Jones, Linda & Jagdeo, Jared. (2019). Safety and penetration of light into the brain. 10.1016/B978-0-12-815305-5.00005-1.

In particular, visible light (wavelength 400 to 700 nm) is substantially absorbed by hemoglobin and other organic matter. On the other hand, absorption by water increases at wavelengths longer than near infrared light (1000+nm). This implies that wavelengths outside of the near-infrared window cannot penetrate deeply through tissue.

Example: “Fire!” When you hold your hand out to a burning fire you feel heat being emitted by the fire. What is happening? The fire emits infrared radiation, which the water molecules absorb in your skin. Then, this is perceived as heat because the nerves in your skin detect the raised temperature.

Penetration through the skull using NIR LED technology

Several independent published studies support the ability of NIR LED technology to penetrate the skull and irradiate the brain.^{[2], [3], [4]} Lasers are not necessary and harbor inherent unnecessary dangers, due to the nature of coherent light energy – power throttling and overheating tend to occur. The common factor is the wavelength range of 800-830nm, which falls within the body’s optical window.

Mechanisms of Brain Photobiomodulation

Brain photobiomodulation (PBM) utilizes red to near-infrared (NIR) photons to stimulate the cytochrome c oxidase enzyme (chromophore/complex IV) of the mitochondrial respiratory chain because this enzyme is receptive to light energy. This outcomes are an increase in ATP synthesis, leading to the generation of more cellular energy. Additionally, photon absorption by ion channels results in release of Ca²⁺ which leads to the activation of transcription factors and gene expression.

There are several mechanisms associated with promoting physiological change through photobiomodulation therapy (PBMT). The wavelengths primarily used with PBM is within the near-infrared range of the electromagnetic spectrum with a sufficient power density. When hypoxic/impaired cells are irradiated with low level NIR photons, there is increased mitochondrial adenosine tri-phosphate (ATP) production within their mitochondria.^{[1], [2]} Another change is the release of nitric oxide from the hypoxic/impaired cells. Neurons are cells that contain mitochondria and nitric oxide.

In hypoxic neuronal cells, cytochrome-C oxidase (CCO), a membrane-bound protein that serves as the end-point electron acceptor in the cell respiration electron transport chain, becomes inhibited by non-covalent binding of nitric oxide. When exposed to NIR photons, the CCO releases nitric oxide, which then diffuses outs of the cell – increasing local blood flow and vasodilation.^{[3], [4]}

Following initial exposure to the NIR photons, there is a brief burst of reactive oxygen species (ROS) in the neuron cell, and this activates a number of signaling pathways. The ROS leads to activation of redox-sensitive genes, and related transcription factors including NF-κβ.^{[5], [6]} The PBMT stimulates gene expression for cellular proliferation, migration, and the production of anti-inflammatory cytokines and growth factors.^[7]

Therapeutic Outcomes of Brain Photobiomodulation

The literature on brain photobiomodulation is growing rapidly. Currently, there are over 220 published studies on brain photobiomodulation.

Brain photobiomodulation has been shown to increase cerebral perfusion and increase connectivity within the Default Mode Network of patients with Alzheimer’s disease and dementia.^[1],[2]

In patients with Parkinson’s disease, measures of mobility, cognition, dynamic balance and fine motor skill y improved (p < 0.05) with PBM treatment for 12 weeks and up to one year.^[3]

There is scientific literature that suggests photobiomodulation might be useful for depression/anxiety.^[4]

Photobiomodulation has also been shown to induce positive physiological changes for traumatic brain injury.^[5]

EEG neural activity can also be influenced by pulsed NIR energy.^[6],[7]

We can expect many more research outcomes of PBM featuring the use of Vielight technology in the near future.

Research & Collaboration

Studies with Vielight technology

Navigation Index

• Alzheimer’s Disease (AD)
• Traumatic Brain Injury (TBI)
• Parkinson’s Disease (PD)
• Autism (ASD)
• Covid-19
• PTSD and Gulf War Illness (PTSD)
• Brain Neuromodulation and Cellular Effects