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Atlas SLI/H 60W Linear Low Pressure Sodium |
This lamp employs a discharge tube whose cross-section takes the shape of a 4-leaf clover. It offers an improvement over the original crescent shape by further increasing light extraction and decreasing current density. Maintenance of sodium position over life is ensured by 32 grooves known as 'greenhouses' running along the edge of each 'leaf'.
A spinoff advantage is a reduction in striking voltage thanks to the unobscured line-of-sight between the electrodes, enabling the use of a low pressure neon-argon-xenon gas filling to bring a further efficacy increase without loss of life. Following Thorn Lighting's takeover of AEI, the new lamps switched to Thorn's Braided cathodes, formed from seven tungsten wires woven into a hollow tube, which contain more emissive material and bring another life extension. The heat-reflective coating is of tin-doped indium oxide.
These improvements brought a modest gain of about 10% in efficacy and earned Thorn the top place in the SLI lamps market, but curiously the company was not successful in the 60W category. Possibly this is due to the fact that Thorn is not believed to have produced lanterns for the 60W lamp. The 60W was a development of its competitor Osram-GEC who did offer a number of lanterns, and even though Thorn had the better lamp, the replacements market continued to be dominated by the GEC SLI/H 60W alternative.
| Manufacturer: | British Lighting Industries Ltd. | |
| Lamp Power: | 60 Watts | |
| Lamp Current: | 0.83 Amps | |
| Lamp Voltage: | 80 Volts | |
| Cap Type: | 2x GY13 | Aluminium + Paxolin |
| Bulb Type: | T-38 | T-12 in eighths/inch |
| Bulb Finish: | Indium-tin oxide film | Soda-lime glass |
| Electrodes: | BC-6 Braided | Black W + BCT emitter |
| Arc Length: | 279 mm | 11 inches |
| Atmosphere: | Na | 99%Ne 0.8%Ar 0.2%Xe | Outer: Hard Vacuum |
| Luminous Flux: | 6,500 lm (@ 100 hrs) | 6,300 lm (average) |
| Luminous Efficacy: | 108.3 lm/W (@ 100 hrs) | |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra -44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.425 |
| Rated Lifetime: | 6,000 hours | 70% survival, 100% flux |
| Warm-up & Re-strike time: | Approx. 15 minutes | Instantaneous |
| Burning Position: | Horizontal ± 20° | |
| Overall Length: | 426.2 mm | 16¾ inches |
| Insertion Length: | 419.1 mm max | 16½ inches |
| Factory: | Leicester | England |
| Date of Manufacture: | September 1973 | Date Code: B1493 |
| Original & Present Value: | £3.99 (1972) | £50.37 (2014) |
