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Sylvania Super Metalarc MS400/HOR 400W |
The shape of an electric arc is influenced by convection currents, caused by the effects of gravity in the gases and vapours in which it operates. A horizontal arc will tend to bow upwards at its centre, this being the reason why electric arcs are so named. Similarly a vertical discharge is usually broader at its upper end than the lower part, again due to the effects of convection. This non-uniform arc shape leads to variations in the temperature of the discharge tube. Since lamps must be designed such that no part becomes overheated, if the arc tube has a large temperature gradient over its surface it means that some regions will be too cool. In a metal halide lamp it is the temperature of the coldest spot that determines lamp performance - and the lower the temperature the worse the performance. However the cold spot temperature can only be raised by making the overall thermal profile more uniform, otherwise it would cause the former hot-spots to become too hot and shorten lamp life.
The lamp pictured here is the Super Metalarc type designed for horizontal burning. The photos clearly show the curved shape of the arc tube, and how it fits around the shape of the arc to achieve impressively uniform thermal uniformity. The effect is that the the cold spot temperature is increased without increasing the hot spot temperature, and luminous efficacy and colour rendering are both considerably improved. To ensure correct orientation of the lamp it is equipped with a modified cap having a protruding side pin - this mates with a slot in a special lamp holder.
| Manufacturer: | GTE Sylvania Inc. | |
| Lamp Power: | 400 Watts | |
| Lamp Current: | 3.4 Amps | |
| Lamp Voltage: | 130 Volts | |
| Cap Type: | EP39s/41 | Ni plated brass + vitrite |
| Bulb Type: | BT-117 | BT-37 (in eighths/inch) |
| Bulb Finish: | Clear | Lead Borosilicate glass |
| Electrodes: | Backwound coil | Thoriated tungsten |
| Arc Length: | 39 mm | 1.54 inches |
| Atmosphere: | (Na,Sc)Ix,Hg | Ar | Outer: Nitrogen |
| Luminous Flux: | 40,000 lm @ 100h | 32,000 lm average |
| Luminous Efficacy: | 100.0 lm/W @ 100h | |
| Colour Temperature & CRI: | 4500K | Ra 65 |
| Chromaticity Co-ordinates: | CCx: 0.360 | CCy: 0.370 |
| Rated Lifetime: | 20,000 hours | to 50% survival |
| Warm-up & Re-strike Time: | 2 minutes | 10 minutes |
| Burning Position: | Horizontal ± 15° | |
| Overall Length: | 292 mm | 111/2 inches |
| Light Centre Length: | 178 mm | 7 inches |
| Factory: | Manchester, NH | U.S.A. |
| Date of Manufacture: | June 1986 | Date Code: SR066 |
| Original Value: | US $42.65 (1979) | |
