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.