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Osira ME/H Compact Source Mercury |
This particular lamp is more commonly known under its Air Ministry reference 5L/457 Bombing Teacher. It was a war time development for the Royal Air Force, who required a lamp of extreme high brightness for use with a projection system from an aircraft. A short arc mercury lamp was chosen over Xenon because of its higher efficiency. To aid in rapidly replacing these lamps, which had a very short lifetime, they are equipped with two pre-focussed caps. The main cap which supplies current is a standard P40s type, and is pre-focussed as normal. A second brass shell is cemented over the crown of the bulb, and a small indent is drilled in its end face. An imaginary line drawn between this and the centre of the main cap intercepts perfectly the axis of the electrodes, and this provided a reliable and vibration-resistant design.
The arc burns between electrodes of solid tungsten to provide a compact source of extremely high brightness. Electrodes have flat ends on account of the high current, and a small overwound coil of tungsten acts as a heat radiator. Seals are of the hand-made vacuum-shrunk type to double molybdenum foils capable of handling the high current. The arc tube is filled only with mercury and argon and was ignited with a Tesla coil. A very rugged mounting was required to prevent arc tube movement during vibration. Metal cups supporting either end are bolted to a steel channel, this is clamped at one end to the stem and at the other to a dimple in the bulb.
| Manufacturer: | The General Electric Company of England PLC | |
| Lamp Power: | 500 Watts | |
| Lamp Current: | 8.2 Amps | |
| Lamp Voltage: | 70 Volts | Tesla coil for ignition |
| Cap: | P40s Prefocus | 38mm shell at bulb crown |
| Bulb Finish: | Clear | Borosilicate |
| Bulb Type: | T-65 | |
| Overall Length: | 260 mm | |
| Light Centre Length: | 120 mm | |
| Electrodes: | Solid tungsten with flat ends | |
| Inner / Outer Atmosphere: | Inner: Ar | Hg | Outer: Nitrogen |
| Luminous Flux: | Not disclosed | |
| Brightness: | Not disclosed | |
| Colour Temperature & CRI: | Not disclosed | |
| Chromaticity Co-ordinates: | Not disclosed | |
| Burning Position: | Horizontal | |
| Rated Life: | No life claim | |
| Warm Up / Re-strike Time: | 2 minutes | 5 minutes |
| Factory: | Wembley, England | |
| Date of Manufacture: | February 1945 | Date Code 38 |
| Original / Present Value: | Not known | |
