Atlas Halogen Photoflood U-Tube - P1/19

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 at 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.
Manufacturer: Thorn Lighting Ltd
Lamp Power: 1250 Watts  
Lamp Voltage: 220-230 Volts  
Lamp Current: 5.56 Amperes  
Cap Type: GX6.35 Ceramic
Bulb Type: TU-8x24 TU-2 in eighths/inch
Bulb Finish: Clear Quartz
Filament Type: C-2U Axial U-Shaped
Atmosphere: Bromine cycle Pure Argon
Luminous Flux: 40,000 lm
Luminous Efficacy: 32.0 lm/W
Peak Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 3400K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.423 CCy: 0.399
Rated Lifetime: 15 hours to 50% survival
Burning Position: Univeral
Overall Length: 75 mm
Light Centre Length:
Factory: Enfield, London United Kingdom
Date of Manufacture: September 1976 Date Code 33
Original / Present Value: Unknown Unknown
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1977, p.257
2) GB Patent 1,122,747 1968 - British Lighting Industries, Halberstadt & Swain - A Tungsten Halogen Lamp