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Thorn 2L U-Shape Compact Fluorescent |
Also in 1984, Osram pioneered a range of higher lamps with U-tube designs in T6 glass tubing. Its 18W, 24W and 36W ratings were introduced in the form of the Dulux L range with G32 caps - superseded a year later by the more compact 2G11 caps. These were copied in 1985 with GE's High Lumen Biax, and in the same year with Philips' PL-L types having a slightly different Pi-shaped design.
Thorn's 2L was a novel adaptation of those predecessors, which applied the 2D technology to improve performance. The efficacy of fluorescent lamps depends on the temperature of the coldest spot of the glass tube, where mercury will condense and determine its vapour pressure. It was found that with these higher power lamps the cold spot and hence lamp performance could be compromised by inadequate air flow around the tubes. Thorn therefore relocated the cold spot to a more stable area inside the lamp cap. The exhaust tubulation is tipped-off longer than usual, as in 2D lamps, to produce a more effective cold spot. In the 2L lamps this tube extends into a brass eyelet in the base which acts as an efficient heat sink, contact being made via a thermally conductive grease. The result was that the Thorn 2L lamps delivered superior luminous flux and efficacy in enclosed luminaires having poor ventilation. Later, the Thorn 2L design was further improved by switching to an amalgam chemistry which offered still better performance, and eliminated the cost and complexity of the cooling eyelet.
| Manufacturer: | Thorn Lighting Ltd. | |
| Lamp Power: | 24 Watts | |
| Lamp Current: | 0.34 Amps | |
| Lamp Voltage: | 91 Volts | |
| Cap Type: | 2G11 | |
| Bulb Finish: | Triphosphor 835 | |
| Bulb Type: | TU-18 | |
| Overall Length: | 320 mm | 12½ inches |
| Width: | 20 x 40 mm | ¾ x 1½ inches |
| Discharge Length: | ||
| Electrodes: | Triple Coil Tungsten | Triple Carbonate Emitter |
| Atmosphere: | Ar | Hg | |
| Luminous Flux: | 1,800 lm @ 100 hours | 1,690 lm @ 2000 hours |
| Luminous Efficacy: | 75.0 lm/W @ 100 hours | 70.5 lm/W @ 2000 hours |
| Colour Temperature & CRI: | CCT: 2950K | CRI: Ra 85 |
| Chromaticity Co-ordinates: | CCx: 0.440 | CCy: 0.402 |
| Burning Position: | Universal | |
| Rated Lifetime: | 7,500 hours | Rated to 50% survival |
| Warm-up / Re-strike Time: | 2 minutes | Instant |
| Factory: | Enfield, London | United Kingdom |
| Date of Manufacture: | August 1989 | |
| Original / Present Value: | £6.41 (1988) | £11.51 (2005) |
