Red light therapy, also known as photobiomodulation (PBM), is a non-invasive treatment that uses light-emitting diodes (LEDs) or low-power lasers to deliver specific wavelengths of light to the body. This process is designed to stimulate cellular function and promote healing. The effectiveness of this therapy relies on using precise light parameters, which are defined not by frequency but by the light’s wavelength.
Defining the Red Light Spectrum
The parameter that defines the light in this therapy is the wavelength, measured in nanometers (nm). Although the public often uses “frequency” interchangeably, wavelength is the technical specification for light-based treatments. Therapeutic red light falls within the visible spectrum, specifically the deep red band, which typically ranges from 630 nm to 700 nm.
This specific band is readily absorbed by certain molecules within the body’s cells. Wavelengths around 660 nm are frequently utilized in commercial and clinical devices for applications like skin rejuvenation. Shorter wavelengths, such as blue light, are absorbed too superficially by the skin’s outer layers.
Near-Infrared Light: The Companion Spectrum
While red light therapy is defined by visible red light, many therapeutic devices incorporate a second, invisible spectrum known as Near-Infrared Light (NIR). NIR light represents longer wavelengths just beyond what the human eye can perceive, generally starting around 780 nm and extending up to about 1200 nm. The most commonly used NIR wavelengths for therapeutic purposes cluster around 810 nm, 830 nm, and 850 nm.
Both red light and NIR are used for photobiomodulation, but they serve distinct purposes based on their physical properties. These two distinct wavelength ranges are often combined in a single treatment device to achieve a more comprehensive effect across multiple tissue depths.
Light Penetration and Cellular Targets
The specific wavelength of light directly dictates the physical depth of penetration into human tissue. This is a crucial factor that determines which cells and tissues receive the therapeutic effect. Shorter wavelengths, such as visible red light (630–700 nm), are absorbed primarily by the skin’s surface layers, including the epidermis and dermis. This makes the visible red spectrum optimal for treating superficial conditions like fine lines, wrinkles, and surface wounds.
Longer wavelengths, specifically the NIR range (780–1200 nm), penetrate deeper into the body. This allows the light to reach underlying structures such as muscle tissue, tendons, joints, and bone. The effectiveness of both ranges is due to the “optical window” in human tissue (600 nm to 1300 nm), where light is minimally absorbed by water and hemoglobin, allowing maximum transmission to deeper cellular targets.
The Biological Mechanism of Action
The physical travel of the light is only the first step; the biological effect begins when the photons interact with specialized molecules called chromophores inside the cell. The primary target for both red and NIR light is the mitochondria. Specifically, the light is absorbed by an enzyme embedded in the mitochondrial membrane called cytochrome c oxidase (CCO).
Under conditions of cellular stress or injury, a molecule called nitric oxide (NO) can bind to the CCO enzyme, which effectively slows down the cell’s ability to produce energy. When photons of red or NIR light are absorbed by the CCO, they cause the temporary dissociation of the inhibitory nitric oxide molecule. This light-induced release frees up the CCO, allowing it to function more efficiently and increasing the rate of cellular respiration.
The resulting cascade includes a temporary boost in the production of adenosine triphosphate (ATP), the primary energy currency of the cell. This increase in available cellular energy supports various downstream effects, including enhanced cellular repair, reduced inflammation, and improved cell proliferation. The temporary release of nitric oxide also acts as a cellular signaling molecule, which can lead to localized vasodilation and improved blood flow to the treated area.