||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 of lamp length 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 established with a thermally conductive grease, to offer a compact lamp having very high luminous efficacy.