The present disclosure is directed to systems and methods for increased vitamin D3 production during phototherapy treatments. In one embodiment, a phototherapeutic system can include an ultraviolet (UV) source directed toward an irradiation zone and a filter between the UV source and the irradiation zone. The UV source can be configured to deliver a predetermined energy level during a phototherapy session. The filter can at least substantially remove UV radiation outside of a predetermined wavelength spectrum. The predetermined spectrum can have a bandwidth of at most 10 nm and can be focused at a wavelength corresponding to a maximum on a vitamin D3 phototherapy action spectrum for the predetermined energy level.
