Blue and red light are synergistic in treating acne due to their respective anti-bacterial and anti-inflammatory effects. LED therapy also has fewer side effects compared to other treatments (e.g. topical or oral medications).
An open-label study using blue (415nm) and red (633nm) light to treat acne showed a 46% reduction in lesions at 4 weeks, and 81% reduction at 8 weeks.
References: Ablon G. Phototherapy with Light Emitting Diodes: Treating a Broad Range of Medical and Aesthetic Conditions in Dermatology. J Clin Aesthet Dermatol. 2018;11(2):21‐27. Avci P, Gupta A, Sadasivam M, et al. Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring. Semin Cutan Med Surg. 2013;32(1):41‐52.