The wavelengths of light differ in their effect.The optimal wavelength ranges for red light therapy
The electromagnetic spectrum includes all wavelengths of electromagnetic radiation. The term light spectrum generally refers to the portion of this spectrum that is visible to the human eye. The visible range begins with violet light at wavelengths of around 400 nanometers (nm) and ends with red light at approximately 700 to 780 nm.
At the shorter end, visible light borders on the ultraviolet (UV) spectrum (around 100 to 400 nm), while at the longer end it transitions into near-infrared radiation (NIR). From about 1,400 to 1,500 nm, the spectrum enters the range of thermal infrared radiation (IR), which produces noticeable warmth.
The wavelengths of light differ in their effects and penetration depth.
They vary in both energy and tissue penetration. Within the so-called therapeutic window, the penetration depth increases continuously from roughly 600 nm up to 850 nm.
For skin applications, red light between 630 and 660 nm has proven highly effective, reaching penetration depths of several centimeters. To additionally benefit from systemic effects and achieve greater depth of impact, red light is now often combined with near-infrared light. The 850 nm range has been shown to be particularly effective.
This combination of wavelengths enhances the absorption of 630–660 nm light in the superficial tissue layers, resulting not only in local effects but also in stronger systemic responses via improved energy absorption through blood vessels. The near-infrared component (850 nm) further contributes by penetrating deeper into the tissue.