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For rjluna2 with a big apology: I've seen, that I've spoiled this pic, the socket is missing 
Nice
I think it might be the modern version Self Ballasted Mercury Vapor Lamp that would work directly to the mains 
http://en.wikipedia.org/wiki/Mercury-vapor_lamp#Self-ballasted_.28SB.29_lamps
As soon as I can to upload this specimen to the Lighting Gallery website, someone would know better than I do