Sylvania Halogen DLX with Hardglass Capsule
Following Sylvania's development of the Capsylite lamp in America, the design was quickly translated into this so-called Halogen DLX model to suit European markets. Whereas the American design was able to achieve a substantial increase in performance thanks to its use of a diode rectifier in the lamp cap which enables the use of a lower voltage and more efficient filament, the same technique could not be applied in Europe. The levels of visible flicker were found to be intolerable, partly due to the lower mains frequency of 50Hz in Europe vs 60Hz in America, but also due to the fact that the higher voltage lamps needed for Europe required thinner filaments which of course have reduced thermal inertia.

At the heart of the lamp is a small single ended tungsten halogen capsule which contains a coiled-coil axial filament. It has a very special segmented design, being single coiled at the support points, so as to minimise heat loss and keep efficacy high. Unusually for a European-made halogen lamp the capsule is fabricated in aluminosilicate hardglass instead of the usually preferred quartz. The American manufacturers perfected the use of this material which is cheaper than quartz and allows a further saving since its lower melting point allows higher production speeds than quartz.

Hardglass capsules have an elevated risk of exploding at end of life and may also shatter a normal outer bulb. This lamp employs a heavy-wall bulb made by a Belgian manufacturer of perfume bottles, which is sufficiently strong. The capsule is ingeniously welded to a metal frame which engages in grooves moulded into the bulb neck, and the ends of this frame are clamped in place by screwing the cap over the threaded end of the glass bulb, without need for cement.
Manufacturer: Sylvania Lighting International
Lamp Power: 50 Watts
Lamp Voltage: 230 Volts
Lamp Current: 0.217 Amperes
Cap Type: E27/27 Ni plated brass + vitrite
Bulb Type: BT-45 BT-15 in eighths/inch
Bulb Finish: Clear Borosilicate
Filament Type: CC-8 3-segment Axial Coiled Coil
Atmosphere: Br2 + PH3 + SiH4 in Kr Outer: Air
Luminous Flux: 675 lm
Luminous Efficacy: 13.5 lm/W
Peak Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2900K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.444 CCy: 0.406
Rated Lifetime: 2000 hours to 50% survival
Burning Position: Universal
Max. Overall Length: 110 mm 4 3/8"
Light Centre Length:
Factory: Tienen Belgium
Date of Manufacture: September 1994 Date Code: 45
Original / Present Value:
References: 1) GTE Sylvania Halogen DLX Brochure, c. 1990 UK
2) SLI Sylvania Lamp Catalogue, 1994.