Capillus laser therapy caps emit lasers in the wavelength of 650 nm, which is a visible red light band. A laser beam at 650 nm penetrates the hair follicle where it is necessary, unlike an LED diode which disperses and does not penetrate to the same depth to be effective.
All of the devices cleared by the FDA for the specific purpose of treating androgenetic alopecia and promoting hair growth operate in the visible light range, specifically at or around 650 nm.
Laser ~650 nm on Hair Follicle. Reaches 5 nm under skin to penetrate to root of follicle.