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Metalarc with Flat Frame Arc Tube Mount |
The 400-watt arc tube is of a rather advanced design for its age, with well formed pinch seals and end chambers around the electrodes to prevent halide condensation here. Coatings of alumina serve as heat reflectors to maintain high temperature behind the electrodes. The arc tube chemistry is based on the sodium-scandium system which was pioneered by Sylvania, and delivers considerably higher initial lumens and better colour control than was available in GE and Westinghouse's chemistries at the time.
Curiously, the arc tube is mounted on Sylvania's famous flat mount frame, developed to increase the ruggedness of mercury lamps. This was standard for all of the very first metal halide lamps. But owing to the close proximity between the arc tube and the charged metal frame, the small sodium ions within the arc tube could be physically drawn into the quartz wall and out of the lamp, resulting in colour changes. In 1966 this problem was overcome by Sylvania's invention of the so-called "frameless" mount assembly. There was no frame alongside the arctube, instead a short upper frame was clamped to one end of the arc tube, and a similar short section between the lower end and the base. The electric current carried to the upper frame was conducted through a thin molybdenum fly-wire spaced as far away from the arctube as possible to minimise the electric field strength.
| Manufacturer: | Sylvania Electric Products Inc. | |
| Lamp Power: | 400 Watts | |
| Lamp Current: | 3.3 Amps | |
| Lamp Voltage: | 133 Volts | |
| Cap: | E39s/41 (Mogul) | Ni Plated + Vitrite |
| Bulb Finish: | Clear | Leaded Borosilicate |
| Bulb Type: | BT-120 | BT-37 (in eighths/inch) |
| Overall Length: | 292 mm | 111/2 inches |
| Light Centre Length: | 178 mm | 7 inches |
| Electrodes: | Backwound coil | Thoriated tungsten |
| Atmosphere: | Inner : Argon | Outer : Nitrogen |
| Luminous Flux: | 34,000 lm @ 100 hours | 25,600 lm mean thro' life |
| Luminous Efficacy: | 97.5 lm/W @ 100 hours | 62.5 lm/W mean thro' life |
| Colour Temperature & CRI: | CCT: 4500K | CRI: Ra 65 |
| Chromaticity Co-ordinates: | CCx: 0.362 | CCy: 0.371 |
| Burning Position | Vertical cap up ± 15° | |
| Rated Life: | 15,000 hours to 50% survival | |
| Factory: | Manchester, NH, U.S.A. | |
| Date of Manufacture: | Circa 1965 | |
| Original / Present Value: | ||