Atlas Low Voltage Display Lamp - Diffuse Reflector

During the early 1960s Thorn Lighting introduced under its Atlas brand a number of high performance luminaires for accent and diplay lighting in professional installations, such as museums and galleries. They were launched with a new family of reflector lamps which made a major advace over conventional light sources by switching to Low Voltage operation. These lamps and fixtures represented the first major usage of 12 and 24V lamps in general display lighting.

The first lamp in the series was in fact a standard type developed earlier for airfield applications - known as the type EL66 or J1/17. That consists of a transverse 12V 50W filament in an ordinary R63.5 blown glass reflector, with clear crown and equipped with a silver plated E27 cap to carry the high current. The compact filament delivers an extremely narrow beam of high intensity, which caught the attention of interior lighting designers as well as the airfield customers. However the clear bulb finish can lead to undesirable images of the filament and dark regions, if the filament is not perfectly aligned. Therefore the second version shown on this page was introduced around 1965, employing a lightly etched bulb to deliver a softer beam but still of comparable performance. In order to raise efficiency to a maximum, the neck diameter of the bulb has been reduced to minimise light loss towards the cap. A smaller cap was required, and the Bosch type was introduced.

Thorn's Low Voltage Incandescent lamps marked the pinnacle of display lighting performance for nearly two decades, but during the 1980s they were gradually displaced by low voltage halogen alternatives. Production was continued for replacement purposes only until around 1988.
Manufacturer: Thorn Electrical Industries Lamp No. 11-8012
Lamp Power: 50 Watts  
Lamp Voltage: 12 Volts  
Lamp Current: 4.16 Amperes  
Cap Type: B20d/27 Ni Plated Brass + Alkyde
Bulb Type: R-63.5 R-20 in eighths/inch
Bulb Finish: High Satinated Aluminised
Filament Type: C-8 Axial single coil
Atmosphere: 95% Argon 5% Nitrogen
Luminous Flux: N/A
Luminous Efficacy: N/A
Peak Intensity: 9,500 cd
Beam Distribution: to 50% peak intensity
Colour Temperature & CRI: CCT: 3000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 1000 hours to 50% survival
Burning Position: Universal
Overall Length: 82 mm 3¼ inches
Light Centre Length: N/A
Factory: Leicester England
Date of Manufacture: November 1972 Date Code 59
Original / Present Value: £0.34 (1972) £5.66 (2014)
 
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1972/73, p.5:11
2) Thorn Lighting Comprehensive Catalogue, UK, 1969/70, p.CG9 & CG16
3) Atlas Technical Pocket Book - 1972
4) Thorn Lighting Comprehensive Price List, UK, 19th April 1972