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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 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, providing a reliable 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 tungsten coil 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 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, clamped to the stem and at the other end 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 | United Kingdom |
| Date of Manufacture: | February 1945 | Date Code 38 |
| Original / Present Value: | Not known | |
