One of the most commercially successful applications of LED light therapy is its use for hair growth.
Studies showed that red light (655 nm) significantly improved hair counts both in men and women with androgenetic alopecia.
Yellow light has also been proven effective for patients with androgenetic alopecia (male-pattern baldness / female pattern hair loss) and alopecia areata (patchy hair loss).
Reference: Sorbellini E, Rucco M, Rinaldi F. Photodynamic and photobiological effects of light-emitting diode (LED) therapy in dermatological disease: an update. Lasers Med Sci. 2018;33(7):1431‐1439.