Ultraviolet phototherapy: review of options for cabin dosimetry and operation.

Ultraviolet (UV) treatment dose is determined by the length of time that a patient spends in a phototherapy cabin. The output from UV fluorescent lamps declines with use and a method is needed to compensate for the change in irradiance and to identify and replace any lamps that fail. The decline in lamp output with age and the magnitudes of localized areas of low irradiance resulting from failed lamps have been measured and results used to assess different approaches to lamp replacement.