Tungsten Halogen Metal Reflector - M/53
Dating back to 1975, the first metal reflector low volt halogen lamps to be introduced by Thorn were the types M/39 and M/41, both based around a 6V 20W capsule in an open mirror stamped from aluminium sheet. They had diameters of 50mm and 56mm respectively, the former employing an ellipsoidal reflector profile for projection applications, the latter having a parabolic surface for special display lighting tasks. Both lamps had unusual bases consisting of a pair of metal tabs to which flexible electrical cables could be connected.

In order to realise a more user-friendly format for general display lighting applications, the M/53 version shown on this page was introduced by Thorn in 1982. It represented a number of key development steps which many later lamps came to rely upon. Perhaps most importantly, it was the first long-life 20W halogen source designed for operation on a 12-volt supply. The 12V 20W filament is made from wire of very fine diameter, and the rate of attack of the cold filament tails by the halogen cycle previously meant that a long life could only be achieved with 6V lamps which employ a thicker wire.

Secondly, this lamp was the first product to feature a sealed design with a glass lens closing the face of the reflector. Low voltage halogen capsules are typically cold-filled to pressures in excess of 4 bar and there exists a risk of explosion during operation. Finally, it marked the first introduction of the SBC cap for halogen reflector lamps. This presented a much more user-friendly option than Thorn's previous products with metal tabs, and is considerably easier to install than types using the two pins of the halogen capsule as the base. M/53 enjoyed only a brief period in production, being superseded in the mid 1980s by the Lightstream MR16 range with dichroic reflectors.
Manufacturer: Thorn EMI M53
Lamp Power: 20 Watts  
Lamp Voltage: 12 Volts  
Lamp Current: 1.67 Amperes  
Cap Type: B15d Ni plated + Vitrite insulator
Bulb Type: ARC-48 ARC-15 in eighths/inch
Bulb Finish: Aluminium reflector Flat glass lens
Filament Type: C-6 Tranverse Single Coil
Atmosphere: Bromine, Krypton
Luminous Flux: N/A  
Luminous Efficacy: N/A  
Peak Intensity: 3,870 cd  
Beam Distribution: 11° to 50% peak
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: 40 mm 1 9/16"
Light Centre Length: N/A
Factory: Enfield, London Great Britain
Date of Manufacture: June 1986 Date Code e6f
Original / Present Value: GB £7.96 (1988) GB £15.38 (2007)
 
References: 1) Thorn EMI Comprehensive Lamp Catalogue - 1984/85
2) Thorn EMI UK Price List - 1988