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Thorn SON with Cermet Arc Tube Seals |
Cermets are composite materials of ceramic and metal, in this case consisting of pressed slugs of alumina doped with tungsten powder. Molybdenum wires are co-sintered into the cermet, to which the electrode coils are attached and electrical connections are made. Because a metal tube or wire does not penetrate the seal in these arc tubes, they have the capability to offer far greater reliability by eliminating seal leaks.
The use of cermet seals did pose one problem though. In the standard niobium-sealed lamps, any hydrogen impurities within the arc tube are able to diffuse out through the metal itself and it does not pose a major problem. Cermets are not permeable to hydrogen though and the first lamps were made with a cermet seal at one end only, to allow hydrogen to diffuse out of the other end. In this final production model which was sold for a few years, both ends are cermet sealed. The hydrogen problem was overcome by incorporating a small coil of barium-titanium wire over the end of one of the electrode shanks. This acts as a superb getter and effectively removes the hydrogen impurities from the arc tube.
Regrettably when GE took over Thorn Lighting in 1992, this innovative cermet sealing technology was abandoned in favour of cheaper standard production in Hungary.
| Manufacturer: | GE-Thorn Lamps Ltd. | |
| Lamp Power: | 70 Watts | |
| Lamp Current: | 0.98 Amps | |
| Lamp Voltage: | 90 Volts | |
| Cap Type: | E327s/27 | Ni plated brass + vitrite |
| Bulb Finish: | Clear | Soda-lime glass |
| Bulb Type: | T-38 | T-12 in eighths/inch |
| Overall Length: | 154 mm | 6 inches |
| Light Centre Length: | 86 mm | 3 3/8 inches |
| Arc Length: | ||
| Electrodes: | Backwound Tungsten | Barium Calcium Tungstate |
| Atmosphere: | Na,Hg | Xe | Outer: Hard Vacuum |
| Luminous Flux: | 6,000 lm | @ 100 hours |
| Luminous Efficacy: | 85.7 lm/W | @ 100 hours |
| Colour Temperature & CRI: | CCT: 1900K | CRI: Ra 25 |
| Chromaticity Co-ordinates: | CCx: 0.542 | CCy: 0.415 |
| Burning Position: | Universal | |
| Rated Lifetime: | 24,000 hours | to 50% survival |
| Warm-up & Re-strike Time: | 8 minutes | 5 minutes max |
| Factory: | Leicester | England |
| Date of Manufacture: | 1991 | |
| Original Value: | Laboratory sample - no commercial value | |
