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Mazda SO/H Sodium Vapour with Dewar Jacket |
Most noticeable is the small nickel cap, thoughtfully attached to the end of the dewar jacket to protect the delicate concealed tip-off which holds the vacuum. A spring supports the long inner vessel, and to prolong the effective life of the vacuum and maximise lamp efficiency, it also employs a barium getter.
Secondly, a pair of sachets of silica gel, held in nickel gauze, are clipped to the U-bend end of the discharge tube. This eliminates the deleterious films of condensation which can otherwise occur inside a lamp after a cold night's street lighting service. Moisture films can make starting very difficult, and later lamps were supplied with discharge tubes having a superior water-repellent silicone coating.
Thirdly, this post-1951 SO lamp is manufactured from BTH's Chesterfield C64 and C40 hard glasses (similar to Pyrex) and these reduced the tendency to crack compared to the earlier C10/C19 soft glasses. In addition it has better adhesion to liquid sodium, preventing it flowing down to one end of the lamp where it can form large light-blocking mirrors. But the C64 lining unfortunately exhibits greater tendency to adsorb argon, which increases lamp striking voltage during life. Lamps made in hard glass are easily identifiable by the greenish grey colour of the "Fernico" glass-metal seals.
| Manufacturer: | The British Thomson-Houston Co. Ltd. | |
| Lamp Power: | 140 Watts | |
| Lamp Current: | 0.90 Amps | 0.81A Starting current |
| Lamp Voltage: | 155/180 Volts | 200-250V Mains voltage |
| Cap Type: | BY22d | Porcelain Medium |
| Bulb Finish: | Clear | Hard glass arc tube |
| Bulb Type: | Inner: TU-17 x 40 | Outer: TA-65 |
| Overall Length: | 518 mm | 20½ inches |
| Light Centre Length: | 280 mm | 11 inches |
| Arc Length: | ||
| Electrodes: | CCC-6 Triple Coil | Black W + BCT Emitter |
| Atmosphere: | Na | 0.8% Ar in Ne, 11 torr | Outer: Hard Vacuum |
| Luminous Flux: | 10,220 lm (@ 100 hrs) | 9,100 lm (@ 4000hrs) |
| Luminous Efficacy: | 73.0 lm/W (@ 100 hrs) | 65.0 lm/W (@ 4000hrs) |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra-44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.425 |
| Burning Position: | Horizontal +20° -5° | |
| Rated Lifetime: | 6,000 hours | Guaranteed to 4,000 hrs |
| Warm-up & Re-strike Time: | 11 minutes | Instantaneous |
| Factory: | Leicester | England |
| Date of Manufacture: | Inner: June 1953 | Dewar: August 1953 |
| Original & Present Value: | £5 7s 6d (1954) | £98.62 (2005) |
