A photo-therapeutic, electrodeless lamp (10) comprising a closed-loop envelope (12) containing an arc generating and sustaining medium that includes mercury. A phosphor coating (14) is provided on the interior surface of the envelope (12). The phosphor coating is capable of generating a first radiation in response to excitation from 254 nm radiation and provides the first radiation having an energy output in the region of 335-430 nm. This wavelength region is most efficient for the treatment of morphea or scleroderma. The output radiated energy from the lamp in the 335-430 nm region is ≧20,000 μW/cm2. In a preferred embodiment of the invention the phosphor is SrB4O7:Eu, which has a spectral response with a peak between 366-368 nm with a bandwidth of about 18 nm.