||The Philips SL*18 lamp was the first one-piece self ballasted compact fluorescent lamp which had the potential to supersede incandescent lamps in many applications. Offering energy savings of 75% and a five-fold longer lifetime it seemed like a commercially sound proposition.
The lamp consists of a 12mm diameter tube folded into three large U-bends to form four parallel sections, with a glowbottle starter and bulky wirewound ballast residing in the base. A prismatic glass jar refracts the light uniformly, and earned the SL its nickname as the lamp resembling a tin of beans - in both shape and weight! A crucial development that made this lamp feasible was 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 always been very fast in tubes of such narrow diameter with traditional phosphors.
Compact fluorescent technology has progressed a long way in the last twenty years. But still, none of them offer the convenience and simplicity of the incandescent lamp which remains at least ten times cheaper than even the most competitively priced retrofits. Although the SL lamp featured here is technologically a great milestone, it is easy to see why it was slow to penetrate the market. Most notable is its great weight - owing to the conventional magnetic ballast inside, the mass of the lamp is more than half a kilogram and this was prone to make many table and standard lamps top heavy and quite unstable. The larger dimensions meant that it wouldn't fit into small shades, and the run-up time of almost five minutes also proved unacceptable.