||With the advent of 8mm indoor cine filming came the requirement for very large lumen packages in a convenient format for the domestic consumer. Initially these took the form of large blown-bulb incandescent reflectors operating at photoflood efficacy, but their size and very short life of 3-5 hours made them quite impractical. These were challenged in the 1960s by short double ended tungsten iodine types, but their flexibility was also hindered by the requirement for operation horizontally ±4°.
Their limitations were eventually overcome by the single ended mains voltage halogen capsules, which could be operated in any position and permitted much smaller hand-held luminaires. But they brought with then new problems of extreme sensitivity to mechanical shocks and vibration, as well as premature failure and explosions resulting from arcing. Generally they employ a coiled-coil filament bent into a U-shape but flimsily supported only at a single point by a tungsten wire fused into the exhaust tip-off. The tails of the filament are welded directly to the moly foils in the pinch-seal, but the short distance between makes the potential for arcing very high. To counteract this they have to be filled with nitrogen, a gas which lowers the efficacy of the lamp.
The problem was solved most elegantly by Alex Halberstadt of the Jules Thorn Labs in Enfield, who invented this U-Tube lamp in 1966. This made possible a return to the method of filament supporting as in double-ended lamps, and solved the shock issue. Furthermore since the distance between the filament tails is greatly extended, the arcing problem was also solved. This permits the U-tube lamps to be filled with argon which raises both efficacy and lifetime.