Thorn 2L U-Shape Compact Fluorescent
Thorn's 2L lamp was a natural progression of the company's earlier compact fluorescent programme, which resulted in the invention of the innovative 2D flat fluorescent lamp . The 2L format was developed to offer an energy saving alternative for linear fluorescent applications, and on account of its twin-tube design can provide more lumens per inch than is possible with standard fluorescents.

This 24W product employs the same T6 tube size as the 28W 2D, with an efficient krypton gasfilling and triphosphor coating. The glass tube is bent into a simple U-shape, similar to the lower wattage Philips PL-S lamps that had also been recently introduced.

The efficacy of fluorescent lamps is depending to a very large extent on the temperature of the coldest spot on the tube wall. The mercury will condense here, and its temperature determines the mercury vapour pressure in the lamp, on which the UV generation efficiency depends. Luminous effficacy rises for a lower cold spot temperature.

Philips PL-S lamps are made with a dead space beyond the bridge joining the tubes, this region running slightly cooler and providing the desired cold spot. In higher power 2L lamps the dead space required here would be quite long, constituting a significant non-lit portion of the lamp. Thorn thus made provision for a cold spot at the opposite end of the lamp through a unique approach. The exhaust tubulation is tipped-off longer than usual, and extends into a brass eyelet in the base which acts as an efficient heat sink, contact being made via a thermally conductive grease, to offer a compact lamp having very high luminous efficacy.
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-16
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, Kr | 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)
 
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1989/90, p.316.
2) Thorn Lighting Price List 1988