A study of the biological effects of low-level light

Low-level light therapy (LLLT), also known as photo biomodulation (PBM), is a type of optical therapy that uses red or near-infrared lasers or light-emitting diodes (LEDs) for medical treatment. The laser wavelengths involved in PBM typically range between 600–700 nm and 780–1100 nm, with power densities ranging between 5 mW/cm² and 5 W/cm². PBM is a series of biochemical cascades exhibited by biological tissues after absorbing a certain amount of energy from light. PBM has been widely used in clinical practice in the past 20 years, and numerous clinical trials have demonstrated its biological efficacy. However, the underlying mechanisms have not yet been fully explored. In this paper, we have summarized the research into PBM over the past two decades, to identify the important mechanisms of the biological effects of PBM from the perspective of molecular mechanisms, cellular levels, and tissue changes. We hope our study provide a theoretical basis for future investigations into the underlying mechanisms.