Osram HQL 50W Half Coated

This special lamp was prepared by German Osram, to illustrate the internal construction which was unique to its low wattage mercury lamps of the 1960s.

The main electrodes are unusual in that they are not made from coiled tungsten wire, but consist of pellets pressed and sintered from tungsten powder combined with barium oxide emitter material. The electrodes are pressed around short metal rods which are welded to the moly foil seals passing through the quartz. At the time of its development it was believed that this would increase the useful life of the lamp by slowing the rate of lumen depreciation - but in fact the advantage was so small for its increased cost, that this design was abandoned within a few years.

Two rather than the usual one auxiliary ignition electrodes are employed for improved starting reliability. These electrodes have unusually been formed by bringing the molybdenum sealing foil right into the arc tube, with an obliquely cut end to form a sharp point. This construction was also abandoned within a few years.

Also visible is the improved thermal insulation of the arc tube, which consists of a heat-reflective mirror of platinum painted onto each end of the arc tube. 50W mercury lamps usually take a long time to run-up due to their low wall loading, and Osram aimed to accelerate that with the heat-reflective coatings, plus an evacuated rather than nitrogen-filled outer bulb. The latter is partially coated with manganese activated magnesium fluoro-germanate, the most preferred phosphor for mercury lamps from the early 1950s until the later 1960s.
Manufacturer: Osram GmbH
Lamp Power: 50 Watts
Lamp Current: 0.6 Amps
Lamp Voltage: 95 Volts
Cap Type: E27/30 Ni plated brass + vitrite
Bulb Type: E-55 E-17 in eighths/inch
Bulb Finish: Mg4(F)Ge06:Mn phosphor Soda-lime soft glass
Electrodes: Sintered Tungsten + emitter pellets
Arc Length: 16 mm
Atmosphere: Inner: Hg | Ar (~16 bar) Outer: Vacuum
Luminous Flux: 1,600 lm (@ 100 hrs)
Luminous Efficacy: 32.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: ~4700K CRI: ~Ra=40
Chromaticity Co-ordinates: CCx: ~0.36 CCy: ~0.42
Rated Lifetime: 7500 hours
Warm-up & Re-strike Time: 5 minutes 5 minutes
Burning Position: Universal
Overall Length: 130 mm 51/8 inches
Light Centre Length: 50 mm 2 inches
Factory: Berlin-Charlottenburg Germany
Date of Manufacture: March 1964 Date Code: nBX
Original Value: DM 17/- (1962)
References: 1) Osram Lamp Catalogue, 1962 Germany
2) Osram Lamp Catalogue, 1965 Germany