||Rough Service Mercury lamps were introduced by Sylvania in 1963, and immediately won acclaim as the toughest lamps available. It was a time when many premature lamp failures were occurring in street lighting service due to mechanical breakdown of the spot-welds which held together the arc tube support frame. Always known for its innovative thinking, Sylvania solved the problem by completely eliminating all frame welds, while its competitors simply focussed on improving them. The Sylvania solution lay in its so-called girder frame, featuring one single piece of stamped metal. No structural welds at all were necessary. The sides of the frame were L-shaped to stiffen the structure and prevent distortion during even the most severe loadings.
The arc tube is mounted simply by bending side strips of the frame over the edges of the quartz pinches. Also included are sprung strips to locate the frame in the crown of the bulb, and a small metal tab over the exhaust tube hole in the stem, to prevent phosphor being blown off the inner bulb surface during introduction of gasfilling stages. The frame is crimped to one lead wire from the stem, and the remaining spot welds for the electrical connections are not load bearing and are thus inherently much more reliable.
The lamps enjoyed great success until the late 1970s, by which time welding technology had progressed and a return to the cheaper welded wire frame was possible. The arc tube here deserves mention only for the great quantity of airlines present along its length - a common feature of early quartz tube drawing at Sylvania. Improved processing today has almost totally eliminated them. Coatings of platinum behind the electrodes provide improved thermal insulation.