||During the energy crisis of the 1970s, Philips engineers at Eindhoven devoted much time to the development of an energy-saving alternative to the GLS lamp. While American firms focussed their attention on miniature metal halide technology, European efforts were directed at compact fluorescent. Philips was the clear leader, and a tremendous variety of different concepts were devised and tested.
By 1976 they had reached their conclusion, and the final prototype is illustrated here. The development was announced during a world conference on lighting hosted in Eindhoven later that year, and this lamp is one of the samples which was demonstrated during the event.
Named the SL1000 (Self-ballastedLuminescent 1000 lumen), it was made possible following the invention by Louis Vrenken of the rare earth phosphors with an aluminate host lattice, in place of the usual silicates or tungstates. These new materials slowed the rate of lumen depreciation, a degradation process that had been quite fast with standard phosphors. It made it possible to increase the tube loading, and permit smaller tube diameters. Consequently the tube was reduced to the T-4 (12mm) diameter, and this could be folded into a compact form suitable for replacing a GLS lamp. A magnetic ballast and glowbottle starter reside in the black plastic base. The outer tube is made of heavy-wall soda-lime glass with an internal coating of fine silica powder to hide the inner tubes and attain better lighting uniformity.
It took five years more to refine the lamp for production and bring its cost down to acceptable levels. In 1981 the Philips SL*18, the first commercial version, was launched.