Lightstream MR16 Dichroic Reflector - M50 EXZ

During the early 1980s several lighting designers began experimenting with MR16 dichroic slide projection lamps for accent and display spotlighting. Previously incandescent reflector lamps had dominated this market, but the dichroic lamps introduced a powerful arsenal of features. Perhaps most noteworthy are their compact dimensions, whiter light, a cool beam, and an attractive sparkling effect thanks to the multifacetted mirror. Their high efficacy also enables a single 50W lamp to replace a 150W mains voltage lamp.

The original projection lamps were high output types having a short lifetime. To allow expansion into general lighting a much longer life was necessary. Working with the London lighting designers, Thorn was one of the first to deliver this with the 1982 launch of the 'Lightstream' range.

Another challenge was that whereas the original projection lamps were intended to be mounted securely by the pressed glass rim, the designers of spotlighting luminaires wished to hold the lamps only by the base pins, fully exposing the elegant facetted reflectors. However the lampholders were not always able to support the weight of the lamps, which would occasionally fall from the ceiling. Bayonet-capped lamps were introduced to avoid this problem, but those made an already expensive lamp even more costly. The problem was solved by Alex Halberstadt's 1984 invention of the grooved glass base illustrated here, which was ultimately copied by all other manufacturers. The beam uniformity of the Thorn lamps was also superior to many competitive versions thanks to the unique Honeycomb reflector facetting - a major step forward over previous designs which used Emett Wiley's original rectangular-shaped facets.
Manufacturer: Thorn EMI
Lamp Power: 50 Watts  
Lamp Voltage: 12 Volts  
Lamp Current: 4.16 Amperes  
Cap Type: GX5.3 Glass base
Bulb Type: MR-51 MR-16 in eighths/inch
Bulb Finish: Open Front 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: 3,700 candelas to half-peak intensity
Beam Distribution: 25.0 x 17.0° to half-peak intensity
Colour Temperature & CRI: CCT: 3000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 3000 hours to 50% survival
Burning Position: Universal  
Overall Length: 44.45 mm 1 3/4"
Light Centre Length: N/A
Factory: Enfield, London United Kingdom
Date of Manufacture: August 1985 5H
Original / Present Value: GB £7.71 trade (1988) £14.90 (2007)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1984/85, p.256
2) Thorn Lighting UK Price List, 1988
3) "Lightstream for Display", B. Haywood & H.R. King, Thorn EMI Lighting Journal No. 27, pp.24
4) "Tungsten Halogen Reflector Lamps", R.A. Hume & A.J. Barrell, Proceedings of the UK National Lighting Conference 1986 pp.246-255