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GEC SOI/H Integral Low Pressure Sodium |
After 1956 the GEC lamps were improved again by placing an extra sleeve of glass around each limb of the discharge tube. This reflected about 50% of the radiated heat back to the discharge tube, while absorbing only some 3% light. The better insulation allowed a larger diameter discharge tube to be used, which lowered the discharge current density and boosted luminous efficacy by about 10%. Ignition was further improved by adding pair of nickel wires spiralled around each limb and connected to the opposite electrode.
A drawback of the integral design was that the turbulent air flow present within the former dewar jackets was no longer present. This used to help create a uniform temperature along the lamp, but the vacuum atmosphere of the SOI lamps causes the electrode ends to tun hotter than the U-bend. The result is that during life, sodium is distilled towards the bend and older lamps suffered sodium depletion at the cap end. This resulted in faster lumen depreciation of the SOI design. It was partly overcome by adjusting the gas fill pressure such that sodium-devoid regions operated cooler, encouraging sodium to migrate back, but was not fully solved until the introduction of SOX lamps in 1964.
| Manufacturer: | The General Electric Company of England PLC | |
| Lamp Power: | 140 Watts | |
| Lamp Current: | 0.9 Amps | 0.81A Starting Current |
| Lamp Voltage: | 160 Volts | 450V ignition |
| Cap Type: | By22d | Mycalex & Brass |
| Bulb Type: | T-65 | T-20½ in eighths/inch |
| Bulb Finish: | Clear | Soda-lime glass |
| Electrodes: | CCC-4 Beehive | Black W + BCT emitter |
| Arc Length: | ||
| Atmosphere: | Inner: Na | Ne Ar1% | Outer: Hard Vacuum |
| Luminous Flux: | 12,400 lm (initial) | 10,600 lm (average) |
| Luminous Efficacy: | 88.6 lm/W (initial) | |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra -44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.425 |
| Rated Lifetime: | 6,000 hours | 70% survival |
| Warm-up & Re-strike time: | Approx. 15 minutes | Instantaneous |
| Burning Position: | Horizontal ± 20° | |
| Overall Length: | 518 ± 10 mm | 20¾ inches |
| Light Centre Length: | 280 ± 10 mm | 11 inches |
| Factory: | Shaw, Oldham | England |
| Date of Manufacture: | July 1972 | Date Code DG |
| Original / Present Value: | £5.25 (1976) | £33.75 (2014) |
