After browsing through some GE lamp catalogs and brochures, I have learned about GE offering some 400w M59 probe start metal halide lamps for the North American market that have a higher lumen maintenance compared to normal 400w M59 probe start metal halide lamps. These lamps are known as StayBright lamps. From what I understand, they were all designed for operation in a vertical base up position only and were offered in high output versions and 360w energy saving versions. Does anyone know how these particular probe start metal halide lamps are able to maintain better lumen maintenance compared to a normal 400w M59 probe start metal halide lamp?

The argon fill pressure was increased to the level of pulse-start MH lamps, this reduces the amount of burner blackening due to sputtering during the run-up phase. In order to ensure a propere discharge ignition on standard CWA ballasts, the lamp is built with a diode circuit which, together with the system's series, forms an open-circuit voltage doubler.