RLOD#35 (2020.06.19) 1983 Sylvania MS400 BD Only

The problem with standard metal halide lamps designed for a universal operation at all positions is that the burner design is compromised to allow such flexibility, which results in the potential of the fill chemistry not being fully realized. This is the case of the standard sodium-scandium iodide lamps that were once ubiquitous in North America. The introduction of this technology resulted in a very significant leap forward in performances compared to mercury lighting, but the gain in initial light output was limited to 48 % compared to deluxe-white (/DX) mercury lamps in the 400 W segment while the technology had clearly more potential.

Sylvania was the first lampmaker to develop and commercialize a properly optimized sodium-scandium iodide lamp, the 175 and 400 W Super Metalarc released in 1974 and designed for a horizontal operation. A 1 kW vertical variant was introduced in 1976, followed by a 400 W model in 1980, offered in two types: base up for high bay lighting and base down (shown here) for a use in uplighters. In the later variant the initial flux output was increased from 34.0 to 40.0 klm (+18 %) with the same mean service life of 20 kh. The flux maintenance was also improved with a mean flux of 80.0 % of the initial level for the SuperMetalarc vs. 75.3 % for the standard Metalarc.

The improved performances are achieved thanks to a shaped quartz burner characterized by an enlarged top section and a narrow (zirconia-coated) bottom electrode chamber, designed to follow the asymmetric temperature distribution around the vertical arc. This design increases the cold-spot temperature and flatten the burner temperature profile. Compared to the properties of the standard tubular burner those changes raise the salt vapor pressure in the plasma, result in a more even additive distribution in the quartz vessel, and mitigate heat losses.