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Lightstream MR16 Dichroic - M57 GBT |
Firstly customers complained bitterly that 2-pin based MR16 lamps were ferociously difficult to install and replace. The fragile pins proved difficult to insert into the lampholders, and would frequently bend or break if not aligned accurately. Secondly it was found that the electrical contact between the pins and lampholder was far from optimal. The contacts are typically fabricated from nickel plated copper, and after several lamp changes the protective plating could be scraped away leaving an oxidised copper surface underneath. The high electrical resistance led to overheating and often welded the lamp pin permanently into the socket. Thirdly many luminaire designs supported the relatively heavy MR16 lamp only by its contact pins, and as the lampholder spring force deteriorated there were many occurrences of lamps falling from the ceiling.
These problems were all overcome with the much more user-friendly bayonet cap. The price increase however was considerable, and this stifled their success. Moreover in the following years the teething problems with the GX5.3 base were overcome anyway. In 1984 Thorn patented the improved GU5.3 base which features a pair of grooves in the neck area, with which small springs in the lampholder coincide to support its weight. The installation troubles were largely overcome by introducing pins with pointed ends, and the electrical connection issues were minimised with the use of more durable lampholder contacts. Consequently the bayonet capped halogen lamps represented only a brief interlude, and have practically disappeared from the market today.
| Manufacturer: | Thorn EMI | LIF : M57 ANSI : GBT |
| Lamp Power: | 50 Watts | |
| Lamp Voltage: | 12 Volts | |
| Lamp Current: | 4.16 Amperes | |
| Cap Type: | B15d | Ni plated + Alkyde |
| Bulb Type: | MR-51 | MR-16 in eighths/inch |
| Bulb Finish: | Open Front | Dichroic Mirror |
| Filament Type: | C-8 | Axial Single Coil |
| Atmosphere: | Bromine, Krypton | |
| Luminous Flux: | 900 lm | (capsule flux) |
| Luminous Efficacy: | 18.0 lm/W | (capsule efficacy) |
| Peak Intensity: | 12,000 cd | |
| Beam Distribution: | 10° | to 50% peak |
| 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 | |
| Max. Overall Length: | 50 mm | 2" |
| Light Centre Length: | N/A | |
| Factory: | Enfield, London | Great Britain |
| Date of Manufacture: | June 1988 | Date Code F8 |
| Original / Present Value: | GB £10.59 (1988) | GB £20.47 (2007) |
