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Narva NF125-00 Mercury with Sintered Pellet Electrode |
The electrodes of most mercury lamps comprise a coil of tungsten wire wound around a thin tungsten shank. The purpose of the coil is to radiate sufficient heat to keep the tip temperature within safe limits, and to reduce heat conduction losses towards the end seals. To maximise lamp efficacy an electron emissive material is also required. Originally a small strip of thorium metal was located under the tungsten coil, but that is quickly sputtered away and causes poor lumen maintenance due to end blackening. The more common solution is to fill the spaces between the coils and shank with a double or triple oxide emitter, usually consisting of barium, calcium and either thorium or yttrium oxides. These oxide coatings are also gradually lost, which limits lamp life, but they instead form a white deposit at the arc tube ends whic greatly improves lumen maintenance.
The Germans made extensive efforts to slow the loss of the emissive material by binding it firmly in a sintered pellet. Whereas Osram electrodes were made entirely of such materials, Narva employed a separate emissive pellet directly behind the electrode coil. The pellet is thus protected from the intense heat of the arc root to extend its life, but remains sufficiently warm that a layer of its constituent metals diffuses over the surface of the tungsten. EDX analysis of the emissive pellet revealed a composition of 17.5% Tungsten, 39.5% ThO2, 21.5% BaO, 21.5% CaO.
| Manufacturer: | VEB Berliner Glühlampenwerk | |
| Lamp Power: | 125 Watts | |
| Lamp Current: | 1.15 Amps | |
| Lamp Voltage: | 125±15 Volts | |
| Cap Type: | E27s/30 | Ni plated brass + vitrite |
| Bulb Finish: | Clear | Borosilicate hard glass |
| Bulb Type: | ED-75 | ED-23½ in eighths/inch |
| Overall Length: | 175 mm | 6 7/8 inches |
| Light Centre Length: | 115±5 mm | 4 3/8 inches |
| Arc Length: | 25mm | 1 inch |
| Electrodes: | Tungsten Coil | Sintered pellet emitter |
| Atmosphere: | Inner: Hg | Ar (8 atm) | Outer: Nitrogen |
| Luminous Flux: | 5,250 lm | @ 100 hrs |
| Luminous Efficacy: | 42.0 lm/W | @ 100 hrs |
| Colour Temperature & CRI: | CCT: 5980K | CRI: Ra 16 |
| Chromaticity & Red Ratio: | CCx: 0.319 CCy: 0.389 | Red Ratio: 0% |
| Burning Position: | Universal | |
| Rated Lifetime: | 12,000 hours | to 70% survival |
| Warm-up & Re-strike Time: | 4 minutes | 4-5 minutes |
| Factory: | Warsaw Bridge, Berlin | East Germany |
| Date of Manufacture: | 1984 Quarter 3 | Date Code: 43 |
| Original & Present Value: | Unknown | |
