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Thorn SLI-HO Linear Low Pressure Sodium |
The most significant change was a diversion from the well established grooved discharge tube of crescent-shaped section to a more efficient design employing a 4-leaf clover section. This incorporated 88 elongated sodium-retention dimples known as 'greenhouses' running along the extremity of each 'leaf'. This still more efficient 5-leaf clover section was later developed for a new 200W High Output lamp, whose performance was further enhanced by the use of an indium oxide heat reflection film. A further advantage of the new design was that the unobscured 'line of sight' between electrodes lowered the lamp striking voltage considerably. Braided cathodes, formed from seven tungsten wires braided into a tube also enhanced cathode life over coiled designs.
The gas filling was also changed at this time to include a xenon component. This very expensive gas suffers fewer energy losses due to elastic and inelastic atomic collisions in the discharge, and efficacy was raised as a result - note the change from neon red to a purple colour discharge before the sodium vaporises. But it also raised striking voltage, so that the HO lamps do not strike on the old switch start circuits, for which the standard 200W lamp also continued in production. These innovations earned Thorn Lighting the top place in the SLI lamps market and the reliability of the Linear design was second to none, suffering from very few early failures. But it gradually diminished in popularity as SOX performance improved, finally ending production in 1985.
| Manufacturer: | Thorn Lighting Ltd. | |
| Lamp Power: | 200 Watts | |
| Lamp Current: | 1.55 Amps | |
| Lamp Voltage: | 145 Volts | |
| Cap Type: | 2x G12 | Aluminium |
| Bulb Finish: | Indium Tin Oxide Film | Soda-lime glass |
| Bulb Type: | Inner: JT-17 Mould | Outer: T-38 |
| Overall Length: | 909 mm | 36 inches |
| Light Centre Length: | N/A | |
| Arc Length: | ||
| Electrodes: | CCC-4 Black Tungsten | BCT emitter |
| Atmosphere: | Na|99%Ne,0.8%Ar,0.2%Xe | Outer: Hard Vacuum |
| Luminous Flux: | 27,500 lm | (@ 100 hrs) |
| Luminous Efficacy: | 137.5 lm/W | (@ 100 hrs) |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra-44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.425 |
| Burning Position: | Horizontal ± 5° | |
| Rated Lifetime: | 8,000 hrs | to 70% survival |
| Warm-up & Re-strike Time: | 12 minutes | Instantaneous |
| Factory: | Leicester | England |
| Date of Manufacture: | September 1980 | Date Code 91 |
| Original & Present Value: | ||
