After receiving my new Na-1 Lab-Arc lamp, I decided to look into it on lamptech.co.uk to get more info. I was amazed by its unusual specs, but that is not the topic of this conversation. According to the website, this lamp was discontinued in 1972, which is pretty late for a lamp first made in 1933.

Anyway, that made me wonder when the modern Gp20Na sodium spectral lamp was first made, because those lamps are in my opinion much more practical than Na-1s, even if they are admittedly a little less cool looking.

Gp20Na lamps aren't on Lamptech, and I don't really know where else to look but here.

Anybody know when Gp20Na lamps started?

Soviet variant of these called DNaS 18 seems to have appeared sometimes in the 1960's so western prototypes are probably from around 1950s. May be late 1940s?

Congratulations on your purchase of Na-1 source BTW! Remember we recommended you to get it?

@RRK
DNaS 18 does definitely look very similar, they all seem to have screw bases instead of the stupid octal base that most Gp20Na lamps have.

If Gp20Na lamps (or lamps similar to it) really did exist as early as the 1950s, then I wonder why GE continued to make the Na-1 up to 20 years later. I really doubt they were getting much business outside of expensive bulb replacements, but I may be wrong.

Thank you, I do remember your recommendation and I am glad I listened!

My guess is the area of optical measurements is rather conservative so once the instrument was established around 1930's with first kinds of LPS lamps, it continued to be ordered by labs over 40 years span.

Also may be this early design had some advantages over later LPS lamps in radiation quality like spectral purity, but here I am not sure. 

I agree with RRK, the lamp design itself dates back to the 40s. In y opinion it is most likely o soviet copy of the german Osram Na Spectral lamp, that was adapted. Then this amp was continued to be manufactured by chinese manufacturers as a cheaper alternative to the rather expensive Osram lamp.

I also agree that in dedicated laboratory lamps the developmental steps are not too big. Reason being is the small market were there is also the redness to pay a bit more for a lamp. The possible profit margin for new investment is rather small.

@RRK
Either of those could be true I suppose.

@Alex
I just looked up the Osram Na spectral lamp and the arc tubes are almost identical to a Gp20Na! This definitely makes sense.

I agree that the GP20Na probably has its origin in the German Osram / Narva spectral series, and the Russian DNaS 18.  It’s very difficult to know which came first though.  During the 1940s German Osram and its former East German special lamps plant which was captured by the Soviets and became Narva, were both severely weakened.  The vast majority of Osram’s production machinery had either been destroyed, or disappeared when it was packed onto railway wagons for transport to the West and to the controlled Philips factories - but never arrived.  It was presumed that those trains were accidentally sent the wrong way, and seized by the Soviets.  It took almost another decade for Osram to gradually resurrect even its general lamps production, before getting back into making the specials.  During that time that time the Soviets surged into the lead, based on the machinery and technical know-how they had acquired from Osram - and also from Tungsram Budapest whose factory was completely emptied of all machinery.

Certainly by the 1960s, the GP20Na was being produced in Japan - which had very close links to the Soviets from whom it imported many lamp technologies.  I have quite an old Toshiba GP20Na.  That is almost identical to the Russian DNaS 18.  China acquired a lot of its mid-century lamp technologies from Moscow but also from Japan.  The latter seems perhaps more likely in this case since the name is the same as used in Japan.

For sure the German/Soviet/Japanese/Chinese design is much simpler than GE’s NA-1 and the older Philips equivalent, however the latter seems to have superior intensity.  It should also be remembered that the USA has an unusual attitude of sometimes leaving a design alone when it works well enough, even though improvements might be possible.  I was shocked when I made my first visits to several of GE’s American plants in the 1990s to see just how ancient some designs were.  For instance I saw their mercury and mercury-cadmium Lab-Arcs were still in production in 1997 with the exact same design as the 1940’s!  The plant engineer laughed that the quartz arc tube seals had been upgraded around 1950 for the general lighting versions - but the profits were so huge on the Lab-Arcs, and there was no real competition, so it was absolutely not a priority to upgrade the design.  It would likely have cost more than the saving, due to the low production volumes. 

It must also be remembered that from the 1950s onwards GE did not sell the NA-1 itself - the business was handled via George W. Gates.  The latter had probably made so many fixtures, in use at every high school and college across the country, that it would have been inconvenient to change the design.  For GE also that would have risked a competitor getting into the market, whereas by sustaining its old design it was assured of a healthy and almost endless business of replacement lamp sales.

@James
Well that makes sense that the Na-1 would be higher intensity since it is 8 more watts than a Gp20Na, but I suppose never really thought of brightness being needed for a spectral source.

I saw those HG and HgCd lamps on your website, that is definitely wild that they never upgraded those seals!