1963 BGW HQA 125W inside frosted high pressure mercury lamp
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In early applications high pressure mercury lamps were often used without phosphors. Early phosphors were used primarily to produce red lines and shift the colour temperature of HPM lamps. with these early lamps like shown here, fluorescent lamps (HQL) and uncoated (HQA) had the same light output of 5250lm.
In applications were no red was needed, or the more green-blue light of the pure mercury discharge lamps was desired these lamps were popular. Also a popularising factor was the lower cost of these uncoated lamps.
Early uncoated lamps were often inside frosted. This allowed to make a more uniform light surface that fitted better to replace incandescent lamps.
This particular lamp was made in 1963 and is so one of the very last lamps being branded BG. In 1964 branding was switched to Narva. It has a typical east german arc tube of the time with narrow pinch seals. and the quartz tubing been longer then the seal itself. ( I will upload a Narva HQRS 400W were this can be seen soon).
This lamp has been inside frosted. I don't think that these lamps are inside etched with Hydrofluic acid. The inside ether is rather course and looks rather like it has been sandblasted. But I am unsure of the exact method used.
there are a few other things to note. The lead in wires ar welded on the socket. this was done rather often with east german lamps. Solder was scars and an expensive foreign good that was scarces ( Socialism at its best). Also when the you click and enlarge the picture you can see a 2 in a triangle. That is a sine that this lamp is only second quality and not first quality. What exactly desired that is unknown.
Clear lamps were still made on offer well into the 90s especially for lighting of water fountains and green parks/plants
many thanks to Olav for scanning and to james for publishing the same broshure about these lamps by BGW:
HERE
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The process was still done with hydrofluoric acid. Mr Schnor himself told me this a few years ago. He was already working as an engineer at BGW in 1963 and later at NARVA.
So much for the introduction. The second photo now also shows an HQA 125W, albeit from BGW in 1965, but already with the clear outer bulb.
Both lamps have the same Arctube with the pinches. This can be seen better on the lamp with the clear outer bulb.