||The lamp illustrated here was never formally offered for sale by Thorn Lighting, it is purely a laboratory sample made up for demonstration purposes.
Technologically it is no different than any standard mercury blended lamp, consisting of a quartz arc tube which is ballasted by an internal single coil tungsten filament. Designed for operation on the high UK mains voltage of 240/250 Volts ignition of the arc tube is therefore relatively straightforward and the third auxiliary electrode is sufficient.
The main electrodes are of the unique construction invented by Thorn and used in many of its discharge lamps, being of the braided tungsten construction. Seven fine thoriated tungsten wires are braided into a hollow tube, which is coiled around the tungsten shank of the electrode, and the hollow structure then impregnated with double carbonate + thoria emissive material (approx 3mg on each electrode). This structure allowed for a greater volume of emitter and reduced the rate of sputtering, allowing lamp performance to be increased. Electrode positioning is outstanding, resulting from a novel laser welding technique employed by Thorn.
The outer jacket is filled with argon:nitrogen and two getters are employed. Standard red phosphorus is applied to the ballast (removing moisture and oxygen) while a zirconium / aluminium getter pan removes hydrogen impurities. Physically the lamp construction is of the most recent design employed by Thorn Lighting, known as the Philips style construction as the inner assembly has been built up on a backbone made of the heavy-gauge inner lead wires, a practice first introduced by Philips.