Philips Compact Fluorescent PL*C 10W

In 1984 a sigificant miniaturisation of compact fluorescent lamps ocurred, with the introduction of the Sylvania double-tube design in which a pair of U-tubes are mounted side-by-side. In 1985 both Sylvania and Osram improved this by fusing the two tubes together to create a single discharge path, raising efficacy by eliminating two of the original four electrodes. For glass-technical reasons it was not practical to apply three U-bends, and both companies adopted the Philips-style glass bridge to join the pair of U-tubes.

Philips began pilot production of a similar design in 1985, and in 1986 launched the PLC type featured here. The letter C means 'cluster' in English, and 'carré' or square in French. It was produced by joining all four tubes with glass bridges, and it is interesting to note from the X-ray image that one of the upper bridges is farther from the end than the other - this enabling the discharge path (and hence lamp power and output) to be increased. A second cold spot is created by the dead zone in the cap area, in case of cap-up operation.

The double-tube lamps immediately became popular due to the great reduction in length, and improved light distribution uniformity. It was this development that suddenly made CFL's much more viable light sources in the rapidly growing market for low energy downlight luminaires in the 1980s. Incidentally there is a small decrease in efficacy vs twin-tube types. This is owing to increased absorption losses of each tube by its neighbours - note the increased core brightness in the lighted photo. Additionally, they tend tend to run hotter with less optimum mercury vapour pressure. In the highest loaded PL*C 26W lamp, this required an amalgam dosing to achieve satisfactory efficacy.
Manufacturer: NV Philips Gloeilampenfabrieken
Lamp Power: 10 Watts
Lamp Current: 0.180 Amps
Lamp Voltage: 67 Volts
Cap Type: G24d-1 Pocan-4235 PBT
Bulb Type: T-12.6 T-4 in eighths/inch
Bulb Finish: Y2O3:Eu3+, CeMgAl11O19:Tb3+ Soda-lime glass
Electrodes: Triple Coil Tungsten Triple carbonate emitter
Atmosphere: Argon + Hg
Luminous Flux: 600 lm @ 100h
Luminous Efficacy: 60.0 lm/W @ 100h
Colour Temperature & CRI: CCT: 2700K CRI: Ra 81
Chromaticity Co-ordinates: CCx: 0.460 CCy: 0.414
Lifetime: 5000 hours Depreciation 4%/1000h
Warm-up & Re-strike Time: 2 minutes Instant
Burning Position: Universal
Overall Length: 95 mm 3.5 inches
Lighted Area:
Factory: Roosendaal The Netherlands
Date of Manufacture: 1986 August Date Code: H6
Original Value: GB £5.51 (1988)
References: 1) Philips Lamp Catalogue 1987/88 International, pp.102-103
2) Philips Pricelist 1988 UK, p.86
3) 50 Jaar Philipslicht in Roosendaal 1948-1998, publ. Philips Roosendaal 1998, pp.39-40
4) 60 Jaar Philips Roosendaal 1948-2008, publ. Philips Roosendaal 2008, pp.72-73