HQLS 250-01 'Silberweiß' Mercury Discharge
Narva began production of its first HQL mercury fluorescent lamps in the early 1950s, using its own phosphor of calcium-strontium-magnesium orthophosphate activated by tin and manganese. The performance was not impressive in either efficacy or colour rendering. They were replaced in 1964 by the HQL Goldweiß (golden white) range, based on a copy of Westinghouse's 1950 magnesium fluorogermanate phosphor to achieve a better red ratio of about 6%.

In 1966 Narva introduced a second parallel range of mercury fluorescent lamps, the HQL xx S, where xx = lamp power in Watts and S = Silberweiß (silver white) - re-named in 1967 to HQLS with the launch of this lamp. Its phosphor is of zinc calcium orthophosphate activated by divalent tin. That was also a relic from the past, having been invented a decade earlier by Sylvania but quickly replaced by that company's superior strontium zinc orthophosphate activated by divalent tin. It was perhaps for cost or patent reasons that Narva adopted the earlier material. Its HQLS lamps achieved a modest 3% red red ratio but with higher lumens than the HQLG Goldweiß range. They are characterised by a broad orange and blue radiation around 620nm and 450nm. After ignition the light colour is a pale orange vs the normal rich magenta of other mercury lamps, and efficacy is improved due to the eye's greater sensitivity to those wavelengths.

HQLS lamps were replaced in 1973 by the Naviflux -03 range (0 = ellipsoidal bulb and 3 = orthophosphate coating). They were discontinued a year later due to Narva's 1971 introduction of its HQLD Deluxeweiß, later the Naviflux -01. Those employed the superior yttrium vanadate phopshor as invented by Sylvania in 1964, which offered the superior combination of both higher red ratio and increased lumens.
Manufacturer: VEB Berliner Glühlampenwerk
Lamp Power: 250 Watts
Lamp Current: 2.15 Amps
Lamp Voltage: 130 Volts
Cap Type: E40s/45 Ni plated brass + porcelain
Bulb Finish: (CaZn)3(PO4)2:Sn2+ Borosilicate hard glass
Bulb Type: BT-90 BT-28 in eighths/inch
Overall Length: 227 mm 9 inches
Light Centre Length: 145 mm 5 3/4 inches
Arc Length:
Electrodes: Backwound tungsten Double carbonate emitter
Atmosphere: Inner: Hg | Ar Outer: Nitrogen
Luminous Flux: 12,200 lm (@ 100 hours)
Luminous Efficacy: 48.8 lm/W (@ 100 hours)
Colour Temperature & CRI: CCT: 5250K CRI: Ra20, Red Ratio 3.3%
Chromaticity Co-ordinates: CCx: 0.340 CCy: 0.399
Burning Position: Universal (reference VBU)
Rated Lifetime: 6,000 hours Rated to 70% survival
Warm-up & Re-strike Time: 3 minutes 4-5 minutes
Factory: East Berlin East Germany
Date of Manufacture: 1967 Q4 (Date code 74)
Original & Present Value: Unknown
References: 1) Narva Hochdruckentladungslampen, 1970.
2) Spectral measurements.