The present disclosure is directed to systems and methods for targeted UVB phototherapy for dermatologic disorders and other indications. In one embodiment a phototherapeutic system can include a radiation source configured to emit light. At least 75% of the light emitted by the radiation source can have wavelength with a bandwidth between 298 nm and 307 nm. The phototherapeutic system can also include a controller operably connected to the radiation source and configured to determine a dosage for a phototherapy session. Dosage can correspond to a product of the intensity of the radiation source and an exposure time of the radiation source and may have an upper bound less than 1 minimal erythema dose (MED). Delivery of the dose of phototherapy can stimulate production of calcitriol and vitamin D3 in the user s skin and can provide an immune response to treat a dermatological disorder.
