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In 1993 a further miniaturisation of the compact fluorescent lamp took place, with the introduction of triple-turn lamps having six parallel limbs. It is not certain which manufacturer took the lead, but Philips listed its PL-T lamps in 18W and 26W ratings in 1993, and GE also announced the launch of this Biax-T model in 13W and 18W for the 4th quarter of 1993. Osram introduced its Dulux-T concept in 1994. All three of these leading manufacturers agreed the electrical and mechanical standards prior to commercialisation, hence all employ the same caps and ballasts with similar lengths.
Approximately 5% decrease in luminous flux was claimed vs the earlier Biax D lamps, due to a small increase in light entrapment between adjacent limbs of the discharge tubes. Both 2-pin versions having internal starters were launched from the outset, as well as this 4-pin variant for use with electronic ballasts. All of the original series Biax T lamps made use of the unique dimpled end bridge design to achieve a cold spot to maximise lamp efficacy, which had been developed several years earlier by Tungsram.
Incidentally, this first version from GE made use of an unusually large diameter plastic base. The reason was to match a similarly proportioned adaptor unit comprising an electronic ballast terminated with a bayonet or Edison screw lamp cap, thereby allowing a retrofit for incandescent lamps. This was found not to be convenient for downlight luminaires, in which the hole in the reflector around the lampholder should be as small as possible. Following the launch of the Osram Dulux T lamps which featured much smaller bases, GE also followed suit and superseded this lamp with a smaller diameter version around 1998. |