|
Stellox High Pressure Sodium |
The arc tube is made of Stellox, a polycrystalline alumina doped with magnesia and yttria to produce a bi-modal grain structure having two distinct particle size distributions. Stellox was developed at AEI Leicester and has similar proeries to GE's Lucalox, the first translucent alumina, but its different grain structure was of crucial importance in circumventing the GE patent. The greater thickness of this arc tube coupled with its rough crystalline surface makes it appear far more opaque than modern tubes.
The arc tube ends are closed with pressed cups of niobium, brazed to the Stellox using an alloy of titanium, zirconium and vanadium. Ti is the element forming the reactive seal to the ceramic, however its melting point is inconveniently high at around 1800-1850°C. The addition of the other metals forms an alloy that can be fused at around 1400°C which is much more desirable for lamp production. Typically, the seal of this type was made by sandwiching three thin washers of each metal over the end of the arc tube and capping them with the niobium cup, before heating in a vacuum furnace. The titanium washer is always the one in contact with the alumina, to form the most reactive seal. One end is blind, while the other is extended into a niobium exhaust tube. This has been pinched-off by cold fusion to permanently seal the sodium amalgam and xenon gas within the arc tube. The electrodes are of primitive design and employ Thorn's braided cathode, originally developed for fluorescent lamps.
| Manufacturer: | British Lighting Industries Ltd. | |
| Lamp Power: | 250 Watts | |
| Lamp Current: | 3.0 Amps | |
| Lamp Voltage: | 100 ±15 Volts | |
| Cap Type: | E40s/45 | Ni plated brass + vitrite |
| Bulb Type: | TD-51 | TD-58 in eighths/inch |
| Bulb Finish: | Clear | Borosilicate glass |
| Electrodes: | Braided Tungsten Coil | BCT Emitter |
| Arc Length: | ||
| Atmosphere: | Inner: Na,Hg | Xe | Outer: Hard Vacuum |
| Luminous Flux: | 25,000 lm (@ 100 hrs) | |
| Luminous Efficacy: | 100 lm/W (@ 100 hrs) | |
| Colour Temperature & CRI: | CCT: 2300K | CRI: Ra 12 |
| Chromaticity Co-ordinates: | CCx: 0.534 | CCy: 0.431 |
| Rated Lifetime: | 5,000 hours | 70% survival |
| Warm-up & Re-strike Time: | 3-4 minutes | 1 minute |
| Burning Position: | Universal | |
| Overall Length: | 257 mm | 101/8 inches |
| Light Centre Length: | 160 mm | 61/4 inches |
| Factory: | Leicester | England |
| Date of Manufacture: | March 1969 | Date Code: P3904 |
| Original & Present Value: | £14.18 (1971) | £179.00 (2014) |
