Philips Compact Fluorescent PL-T 18W/35

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 this PL-T lamp in 18W and 26W ratings in 1993, and GE also announced the launch of its Biax-T lamps 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.

Whereas GE, Osram and later followers joined three tightly folded U-tubes to form a hexagonal arrangement, Philips employed three wide bends in parallel. Such a design had been introduced in 1992 for its self-ballasted PL*E/T lamps, and adopted the amalgam technology of its earlier SL* lamps. This was of great importance since these very compact lamps operate at higher temperature, and their efficacy decreases sharply when used in small luminaires. In some cases the luminous flux of Philips lamps was higher than competitive designs when installed in a luminaire.

Nevertheless, the Philips design also had some drawbacks. The light distribution is highly asymmetric, and this was not favoured in downlights. Moreover the phosphor coating is applied before tube bending, and can become too thin on the outer radii of the bends. Still another drawback is that the large light-emitting surface around the bends does not irradiate so well the reflectors of certain luminaires, resulting in a less well defined beam profile. These factors resulted in Philips eventually following the hexagonal construction of its competitors, with the launch of the PLT-Hex lamps in 2003.
Manufacturer: NV Philips Gloeilampenfabrieken
Lamp Power: 18 Watts
Lamp Current: 0.210 Amps
Lamp Voltage: 80 Volts
Cap Type: GX24q-2 Pocan-4235 PBT
Bulb Type: T-12 T-4 in eighths/inch
Bulb Finish: CAT, BAM, YOX phosphors Soda-lime glass
Electrodes: Triple Coil Tungsten Triple carbonate emitter
Atmosphere: Argon + Hg
Luminous Flux: 1200 lm @ 100h
Luminous Efficacy: 73.6 lm/W @ 100h
Colour Temperature & CRI: CCT: 3500K CRI: Ra 82
Chromaticity Co-ordinates: CCx: 0.411 CCy: 0.398
Lifetime: 11,000 hours
Warm-up & Re-strike Time: 2 minutes Instant
Burning Position: Universal
Overall Length: 117 mm 4.61 inches
Lighted Area:
Mass: 68 grams
Factory: Terneuzen The Netherlands
Date of Manufacture: 1996 December Date Code: 6M
Original Value: GB £11.89 (2005)
References: 1) Philips Catalogue, 1993/94 UK, pp.9·62-9·63
2) Philips Price List, 1995 November UK, p.107