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Philora Direct Current Sodium Vapour |
A single central cathode is mounted at the centre of the bulb and is coated with alkali-earth oxides for good electrode emission. For optimum thermal uniformity, the discharge is struck to two ring-shaped anodes located at either end of the bulb, each positioned about 2cm away from the cathode. In the very first lamps the anodes were simple loops of wire, but from 1932 the molybdenum strip design shown here was introduced. Lamps had to be operated on DC, which ensured that the sodium remained in the vicinity of the central cathode. AC operation would result in very short life by allowing sodium to diffuse towards the ends of the bulb and attack the seals.
A conventional flare and stem design is employed to seal the bulb. However this was troublesome owing to the existence of a cold region at the base of the seal where sodium could condense, as well as the proximity of the glass-metal pinch seal to the heat of the discharge. These problems have been minimised by inclusion of a heat-reflective mica plate between the discharge vessel area and the seal area. The disc is pierced by a small ceramic tube which allows the seal area to be exhausted but the tube diameter is sufficiently small to prevent significant diffusion of sodium vapour into the seal area during the relatively short lamp life. These lamps can only be operated within a dewar jacket to provide the necessary degree of thermal insulation required to attain the correct operating temperature and sodium vapour pressure.
| Manufacturer: | N.V. Philips Gloeilampenfabrieken | |
| Lamp Power: | c. 82 Watts | (Filament 16W, Arc 66W) |
| Lamp Current: | Arc 5 Amps | Filament 9.6 Amps |
| Lamp Voltage: | Arc 14 Volts | Filament 1.8 Volts |
| Cap Type: | UX4 | British 4-Pin Valve Base |
| Bulb Type: | T-38 mm | T-12 eighths/inch |
| Bulb Finish: | Clear | Borate Glazed Soda-lime |
| Electrodes: | Coiled-Coil tungsten | BaO emitter |
| Arc Length: | 2 x 20mm | 2 x 0.75 inches |
| Atmosphere: | Na 0.5 grams | Neon 1.5 torr |
| Luminous Flux: | c. 4,000lm | @ 100 hrs |
| Luminous Efficacy: | c. 40.0 lm/W | @ 100 hours |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra -44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.475 |
| Rated Lifetime: | Approx 900h | to 50% survival |
| Warm-up & Re-strike Time: | c. 15 minutes | Instantaneous |
| Burning Position: | Vertical ± 45° | |
| Overall Length: | 150mm | 6 inches |
| Light Centre Length: | 120mm | 4 inches |
| Factory: | Eindhoven | The Netherlands |
| Date of Manufacture: | c. 1932 | |
| Original & Present Value: | Unknown | |
