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 electronic ballast for the SLR25143V lamp. Order against the lamp designation rather than the reactor model: Wedeco has built reactors of the same model with more than one lamp rating, and the ballast must match the lamp. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.