1994 Osram NAV-E 110W

The research and development capacity for high-pressure sodium lamps at Osram in Germany was quite limited during the 1970s and 80s, to such an extent that the Germans relied on other manufacturers to produce some of its non-standard sodium lamps. Following the selling agreement of GEC's lighting operation (Great Britain) to Osram GmbH, struck on March 19th, 1986, the Germans leveraged the more advanced HPS lamp production at GEC to complete their product catalog. The British thus manufactured all Vialox Super (high-efficiency), De Luxe (improved light color), and Plug-In (mercury lamp retrofit) for Osram. Those operations were then fully integrated to those of Osram Germany in 1990.

The NAV-E 110W shown here belongs to the latter type of Vialox lamps, first released by the Germans in 1985. Instead of using the usual self-starting circuit design implemented by GEC in their lamps (i.e., xenon-filled burner and internal snap switch starter), the burner here is filled with a neon-argon Penning mixture following a design principle first established by Philips (the Netherlands) in the late 1960s. This, combined with an external capacitive antenna that enhances the electric field in the arc tube, ensures a reliable ignition on 220 V mains circuit without the need for an external electronic ignitor. Interestingly, instead of the usual wire coil antenna and bimetal switch construction, the Vialox features a linear wire antenna held by a single bimetal strip that retracts as the lamp warms up. This measure prevents the accelerated loss of sodium from the burner via electrolysis. Like most retrofit sodium lamps made in Europe, this model has the same bulb and dimensions as those of the mercury lamp it replaces (125 W type, in the present case). A diffuse coating of silica ensures a good optical compatibility with luminaires designed for fluorescent mercury lamps. Typical of GEC's design for high-pressure sodium and mercury lamps, the coating is very thin to allow an effective imaging of the bright arc tube in projection optics, thus enabling an improved light distribution compared to more opaque lamps. Osram kept this design feature, even in their mercury lamps, well after the takeover of GEC's lighting operations.

The 110 W Penning sodium lamp is the smallest of its kind. The use of a neon-based buffer instead of the usual xenon fill causes such an increase of heat conduction losses from the plasma that these retrofit lamps are characterized by significantly lower efficacy and a poorer flux maintenance than their standard counterparts. The relative gap in performances between the two technologies widens at lower wattages, and for this reason manufacturers usually don’t produce neon-filled sodium lamps below 150 W. Only Osram, Sylvania (Belgium), and Tesla (Czechoslovakia) offered lower-wattage lamps based on this technology in order to provide a retrofit solution to 125 W mercury lamp systems, even if the benefits were limited. With an initial lumen efficacy of 73 lm/W, the performance of this NAV-E 110W is indeed quite poor compared to that of the 100 W Super NAV/SON (95-100 lm/W) released several years earlier and intended for the upgrade of old 125 W mercury lighting installations. The retrofit lamp offered a much cheaper upgrade solution as there was no need to change the control gear or even the luminaire, and its substantially increased output flux (+27 %) combined with a significant decrease in power consumption (-12 %) compared to 125 W mercury lamps made the NAV-E 110 W a successful product.

Osram’s Vialox Plug-In lamps production continued in England after Osram took over GEC’s lighting operations in 1989. As the demand for this lamp type grew, a second production line was setup during the 1990s at the company's HID lamp factory in Berlin Spandau. That operation absorbed the full production capacity when the factory in Shaw, England, closed down in 2000. Around the middle of this decade the production of neon-filled sodium retrofit lamp was then moved eastward to Slovakia and to China. The application in April 2015 of the EU Directive EC245/2009 which set a minimum requirement on lamp efficacy spelled the end of this type of sodium lamp in Europe. The retrofit market for 80 and 125 W mercury lamp still in use was then catered for by the more efficient and durable self-starting 68/108 W unsaturated-vapor xenon-filled sodium lamp that was developed by SLI Sylvania in 2001, a technology eventually adopted by other manufacturers.