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Thorn Metal Halide Kolorarc MBI/BD 400W |
Sodium-Scandium lamps have the advantage of higher luminous flux than competing tri-band and rare earth chemistries, but were not developed elsewhere in Europe because of the challenges associated with running them on simple choke-type ballasts. However Thorn took the lead in solving many of these problems. The principal difficulty is that scandium iodide reacts with hot quartz to form stable scandium oxide + silicon iodide. The latter reacts with the tungsten electrodes, in which the silicon dissolves, releasing elemental iodine. Iodine is strongly electronegative, and the gradual increase in its concentration limits lamp life by its effect on increasing the reignition peaks of the arc voltage.
Thorn's first lamps required a special autotransformer ballast to deliver a high open circuit voltage, but this requirement was lifted in 1972 by the development of exceptionally clean lampmaking processes. These included polishing of arc tubes with ammonium bifluoride and hydrofluoric acid, and the world's first use of anhydrous metal halide pellets - a process developed jointly by Thorn and APL Materials. Thorn was also unusual for sandblasting its arc tubes to improve colour homogeneity in precision optical systems. This made lamps such as this Base Down model the favoured light source in demanding applications such as Lighthouses.
| Manufacturer: | Thorn Lighting Ltd | Lamp No. 91-7142 |
| Lamp Power: | 375 Watts | |
| Lamp Current: | 3.5 Amps | |
| Lamp Voltage: | 120 Volts | 3.5-5.0kV ignition |
| Cap Type: | E40s/45 | Ni Plated Brass + Vitrite |
| Bulb Type: | ED-120 | ED-37 in eighths/inch |
| Bulb Finish: | Clear | Borosilicate glass |
| Electrodes: | Backwound Tungsten | Thoriated Tungsten |
| Arc Length: | ||
| Atmosphere: | Inner: Hg,(Na,Sc)Ix | Ar | Outer: Nitrogen |
| Luminous Flux: | 29,000 lm (@ 100 hrs) | 24,000 lm (@ 2000h) |
| Luminous Efficacy: | 77.3 lm/W (@ 100 hrs) | |
| Colour Temperature & CRI: | CCT: 4100K | CRI: Ra 65 |
| Chromaticity Co-ordinates: | CCx: 0.380 | CCy: 0.385 |
| Rated Lifetime: | 7,5000 hours | 70% flux & 80% survival |
| Warm-up & Re-strike Time: | 2 minutes | 8.5 minutes |
| Burning Position: | Base Down to 15° above horizontal | |
| Overall Length: | 292 mm | 7 3/8 inches |
| Light Centre Length: | ||
| Factory: | Leicester | England |
| Date of Manufacture: | January 1979 | Date Code: 61 |
| Original Value: | ||
