Red Light Therapy is a non-invasive treatment that uses specific wavelengths of light to stimulate biological processes within the body. This therapy works by delivering photons to the cells, where they are primarily absorbed by the mitochondria, the cell’s energy factories. The absorption of this light energy enhances mitochondrial function, leading to increased production of adenosine triphosphate (ATP), which is the primary energy currency of the cell. The wavelength of light used is the single most important factor determining how deeply the light penetrates the tissue and, therefore, how effective the treatment will be for a particular condition.
The Two Key Therapeutic Light Ranges
Red Light Therapy utilizes two major categories of light: Red Light and Near-Infrared (NIR) Light. Red Light is visible to the human eye and occupies the approximate range of 600 nanometers (nm) to 700 nm. This is the deep red glow emitted by many at-home devices.
Near-Infrared (NIR) Light falls into a longer wavelength range, typically spanning from about 780 nm to 1000 nm. NIR light is invisible to the human eye, meaning a device emitting it will appear dark or only faintly glowing. These two distinct ranges are used to target different depths within the body.
How Wavelength Influences Penetration Depth
The “therapeutic window” describes the range of red and near-infrared wavelengths that can penetrate human tissue most effectively. Light interaction is a balance between absorption and scattering by chromophores—light-absorbing molecules—in the body. Shorter wavelengths, such as visible red light, are strongly absorbed by melanin in the skin and hemoglobin in the blood.
This high absorption makes visible red light excellent for treating superficial issues like skin health, fine lines, and surface inflammation. Longer wavelengths, specifically those in the NIR range, scatter less and are absorbed less by water and blood. Because of this decreased absorption, NIR light can penetrate much deeper, reaching underlying muscle, joint capsules, and bone tissue.
Identifying the Peak Therapeutic Window
The most effective wavelength involves specific peaks where the mitochondrial enzyme, Cytochrome C Oxidase (CCO), is maximally stimulated. Research has identified two primary optimal peaks for photobiomodulation: 660 nm and 850 nm.
The 660 nm wavelength, a deep red color, is highly effective for targeting superficial cells. This peak maximizes CCO activity in the skin and upper layers of tissue, promoting collagen production and healing of surface wounds.
The 850 nm wavelength, in the invisible near-infrared spectrum, is optimal for stimulating CCO in deeper tissues. This longer wavelength allows the light to reach muscle, bone, and joint structures, supporting recovery and reducing deeper inflammation. Many devices combine 660 nm and 850 nm to provide a comprehensive treatment addressing both surface-level and deep-tissue targets simultaneously.
Other Essential Device Specifications Beyond Wavelength
While wavelength determines the depth of penetration, the effectiveness of a Red Light Therapy device also depends on its Irradiance, or power density. Irradiance is measured in milliwatts per square centimeter (mW/cm²) and quantifies the amount of light energy delivered to the tissue surface. A device using the optimal wavelength will be ineffective if it does not deliver sufficient power.
For full-body treatment, an irradiance between 30 and 40 mW/cm² is often considered the optimal range to ensure adequate energy reaches the deep tissue. Higher irradiance levels, sometimes exceeding 100 mW/cm² for targeted devices, allow for shorter treatment times. The total energy dose received, measured in Joules per square centimeter (J/cm²), is calculated by multiplying irradiance by the treatment time.