GE Halogen MR16 with Twist & Lock Base - TAL 423

The first MR16 lamps were designed for use in projectors, in which they were securely mounted by the refector rim. Later versions were applied in general spotlighting, and luminaire designers preferred to hold them only by the base pins such that the sparking dichroic reflector was fully exposed. However the GX5.3 lampholders had not been designed to support the weight of the lamps, which would occasionally fall from the ceiling with a consequent risk of fire or injury.

This situation was partially improved with the 1984 invention of the GU5.3 grooved glass base by Thorn Lighting's Alex Halberstadt. However customers complained that it was still difficult to install the fragile pins blindly into two tiny holes. Often the pins became bent and the lamps destroyed, or the poor contact led to problems of arcing which damaged the lampholders. A notable improvement was made with the introduction of Bayonet-capped lamps, but the addition of the extra cap made an already expensive lamp even more costly, and compromised life by raising seal temperatures.

The problem was finally solved by another Thorn engineer Roger Hume, with this "Twist-and-Lock" lamp having a GU7 base and holder interface. The concept was based on the robust and reliable caps of fluorescent starter-switches, whose pins also have to be inserted blindly into holes, and where the twisting action achieves guaranteed electrical contact and eliminates all possibility of loose or falling lamps. The simple addition of TIG-welded brass pins had minimal cost impact, and avoided raising seal temperature. The GU7 platform became popular in America, but in Europe the simultaneous introduction of Sylvania's GU10 mains voltage lamps eventually won the main share of the market.
Manufacturer: General Electric
Lamp Power: 50 Watts  
Lamp Voltage: 12 Volts  
Lamp Current: 4.16 Amperes  
Cap Type: GU7 Glass base
Bulb Type: MRC-51 MRC-16 in eighths/inch
Bulb Finish: Frosted Capsule Dichroic Mirror
Filament Type: C-6 Transverse single coil
Atmosphere: Krypton:Argon Bromine cycle
Luminous Flux: 900 (capsule flux)
Luminous Efficacy: 18.0 (capsule efficacy)
Peak Intensity: 630 candelas to half-peak intensity
Beam Distribution: 60° to half-peak intensity
Colour Temperature & CRI: CCT: 3000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 3500 hours to 50% survival
Burning Position: Universal  
Overall Length: 50.5 mm 2"
Light Centre Length: N/A
Factory: Leicester United Kingdom
Date of Manufacture: May 1993 Date Code: E3
Original Value: GB £8.48
References: 1) GE-Thorn Brochure, Twist-and-Lock Mirror Lamps, 1991 (UK)
2) GE-Thorn Brochure, Halogen Display Lamps, 1991 (UK)
3) GE-Thorn Price List, March 1992, UK, p.18
4) Patent WO1992-014,967 Improvements in Lamps & Holders in Display Lighting, R.A.Hume R.A.Felstead D.G.L.Lee L.C.Barling A.J. Barrell, 21-II-1991
5) Private Communication, Roger Hume, GE Lighting Leicester, 1998