The ballast sets and holds the current the ultraviolet lamp arc runs at. A ballast drifting out of specification changes delivered UV-C output without failing outright, so the plant keeps running and quietly under-doses. This is the OMB 150/50 ballast. Note that this catalogue lists a second OMB 150/50 ballast under item 13413-0122 at the same price; quote the item number when ordering. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.