The apparatuses disclosed herein include a discharge lamp configured to emit ultraviolet and visible light, an optical filter configured to attenuate visible light, and a power circuit configured to operate the discharge lamp. Some embodiments of the apparatuses are configured such that ultraviolet light emitted from the discharge lamp and passed through the optical filter encircles an exterior surface of the apparatus. Some cases of the apparatuses include a sensor system configured to monitor a first parameter associated with the operation of the discharge lamp and a second parameter associated with the transmittance of the optical filter. Some of the apparatuses include a means for moving the optical filter while the apparatus is in operation. In some cases, the apparatuses may be configured such that the optical filter may be arranged in and out of alignment with the discharge lamp. In some embodiments, the optical filter may be a multifaceted.