Single Ended Halogen Capsule - M/32

The earliest tungsten halogen lamps were available only in the form of a linear quartz tube, pinched closed at both ends and containing an axial filament. While this arrangement was perfectly suitable for large area floodlights, they lacked the point-like nature of conventional incandescent lamps. Additionally, the manufacturing process required the fabrication of two glass-to-metal seals, which were rather difficult and expensive to form at this time.

In 1961 H.G. Jenkins, working at the Hirst Laboratories of the General Electric Company in Wembley, presented a new direction in halogen lamps with his Single Ended concept. By pinching both tails of the filament into one single seal the contruction was greatly simplified, and the introduction of a low voltage filament made the lamp remarkably compact. The first commercial lamp was the type A1/215 (FCR), a 24V 250W capsule intended for slide projection applications.

While the GEC quickly expanded its range to offer miniature halogen capsules to replace a number of photographic and projector lamps, another pioneer, Thorn Lighting, recognised the potential for these capsules in general lighting mass markets. The single ended concept was ably exploited by Alex Halberstadt of the Enfield laboratories, and Thorn's first product was the 12V 50W capsule featured here.

Thorn had introduced a few years earlier a number of accent & display luminaires using 12V incandescent reflector lamps, offering tremendous performance increases over mains volt reflector lamps thanks to the higher efficacy and smaller size of the low volt filaments. It was quick to build new luminaires around its 12V 50W halogen capsule, which became very popular in the UK from the early 1970s. Low voltage halogen has since become a global standard for interior accent and display lighting, spurred on by GE's later invention of the MR16 lamp with integrated dichroic reflector.
Manufacturer: British Lighting Industries Ltd.
Lamp Power: 50 Watts  
Lamp Voltage: 12 Volts  
Lamp Current: 4.16 Amperes  
Cap Type: GY6.35 Gold plated molybdenum
Bulb Type: T-10.5 T-3.5in eighths/inch
Bulb Finish: Clear Quartz
Filament Type: C-6 3.5 x 2.5mm
Atmosphere: Bromine in Ar
Luminous Flux: 900 lm  
Luminous Efficacy: 18.0 lm/W  
Peak Intensity: N/A  
Beam Distribution: N/A  
Colour Temperature & CRI: CCT: 3000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 2000 hours to 50% survival
Burning Position: Universal  
Max. Overall Length: 44 mm 1 3/4"
Light Centre Length: 30 mm 1 3/16"
Factory: Tottenham, London United Kingdom
Date of Manufacture: April 1969 Date Code D9
Original / Present Value: GBP 18s 0d (1969) GBP £10.67 (2007)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1969/70, p.CG13