Red light therapy uses either red light, near-infrared light, or a combination of both. But what exactly is the difference between red light and near-infrared light?
All light travels as a wave of electromagnetic radiation, and the distance between wave peaks is known as the wavelength. The color and type of light are characterized by its wavelength.
Red light has wavelengths in the range of about 620–700 nm, while near-infrared light has wavelengths in the range of about 700–1,400 nm. The defining difference between the two types of light is that red light is visible to the human eye and infrared light is not.
Our bodies are mostly impenetrable to visible light, including red light. However, longer-wavelength light (i.e., closer to near-infrared than red) can more readily penetrate deeper into the body.[1][2][3][4] As a result, red light therapy for topical applications (e.g., hair loss, skin health, eyes) will tend to use red light (since a greater proportion of energy is delivered to skin cells), while red light therapy targeting tissues inside the body (e.g., joints, muscles, brain) will tend to use infrared light.