This lamp appeared in the Osram catalog during the 90'. Osram called it Sodium-Xenon lamp. This lamp was offered either with E27 elliptical coated or PG-12 tubular and producted the same color light of the incandescent lamps. Once the production of this lamp was discontinued, it completely disappeared from Osram website and today, it is not be mentioned and appears in any lighting related websites including here (LG) and the GoL site where there are no pictures of it. The only place on the internet where the City Light DS lamp is mentioned is on the environmental awards page on the Osram website were this lamp caused Osram to win the "European Better Environmental Award for Industry '96" for an unknown reason to me because the most close reason for Osram to win such award, for me is the mercury and HG free white HPS are really non exists in the market. The only white HPS from Osram that mentioned in anywhere on lighting related websites is the Osram DSX which contains mercury (Like all white HPS lamps) and can produce 2700K and 2900K CCT light.
Is anyone know or heard about this lamp?

Why anyone don't answer me?

You should do a search instead for its more common name "Colorstar DSX".

In 2009 it was still being manufactured for replacement purposes although indeed not listed in Osram literature any more.  There were two versions : first was the DSX-T 80W, a lamp whose colour temperature could be switched from about 2600K to 3000K, intended for shop lighting.  It was not a commercial success, the shift in colour was too small to really entice many customers to install a full new lighting system.

Few years later Osram replaced it by a modified version which was dimmable, the DSX2-T 80/50W.  The luminous flux could be reduced by dimming down to 50W but without substantial colour shift.  Osram tried then to market this lamp technology as an energy saving version for street lighting, but again it was not really a great success.  The lamps were very expensive and required similarly expensive electronic gear as well as complete new luminaires due to the different cap type.

Today both concepts seem to have been largely abandoned by Osram.  You almost never see this going into new installations but I believe they are still making both lamps for replacements for customers who did invest in this system.  I have examples of each type and will try to find time to add them to my website in due course!

James: I think the Colorstar DSX2-T is the lamp that refered to be the Citylight DS in the Osram website.
Also the reasons for the mysterious environmental award winning is now known to me. When i googled Colorstar DSX i found this website: http://www.mx-electronic.com/pdf/Drehspiegelengl.PDF with a pdf file. The Colorstar DSX2-T which is probably what refered in Osram website to be the Citylight DS is indeed a mercury free white HPS lamp (And so were called by Osram "Sodium-Xenon" lamp). So why Philips and Iwasaki don't produces their SDW and SDX white HPS lamps without mercury?
Today Philips SDW-T and SDW-TG is popular in Israel in recessed ceiling floodlights in supermarket.

I guess that Philips and Iwasaki could make a mercury free White SON lamp as well, but choose not to (although they have since copied the standard mercury-free SON invented by Sylvania).  Trouble with Hg-free lamps is that they tend to be a little bit less efficient than standard versions. 

You have to remember that lamps cause a release of mercury into the environment not only because of the few milligrams of metal contained in each lamp, but also because of the energy consumed during life.  Much of the world's energy today is still produced by combustion of fossil fuels and these contain traces of mercury as well - simply burning them results in that mercury being released into the atmosphere.  So if you consume more energy in a lamp, you also increase its total mercury footprint.  For instance, a typical 100W incandescent lamp contains zero mercury, but will cause emission of about 60mg mercury into the environment during a 10,000 hour period.  A CFL alternative only contains <3mg mercury but will still result in about 15mg mercury release due to power generation.  So in this case, the lamp containing more mercury actually results in less total mercury emission.

In the case of HPS lamps, when you factor in the large amounts of energy being consumed, you find that the so-called mercury free lamps are in fact, in many cases, not a good choice from the environmental standpoint.  There is indeed no mercury inside the lamp but their lower efficacy can result in more mercury being emitted due to elecricity generation!  Consequently we find that the Hg-free lamps are very popular in countries such as France and Belgium where virtually all energy production is Nuclear, and in the Nordic countries which have high proportions of hydro power, but in other locations the Hg-free lamp makes no sense.  This situation was not recognised until fairly recently, and perhaps not known at the time of launch of Osram's Colorstar DSX!  It's maybe another reason why Osram is no longer promoting this concept so heavily.  Certainly the big streetlighting authorities who are aware of this situation would be the biggest potential customers and if they don't accept this lamp, the remaining market would not be big enough to survive on.

By the way, the original DSX with switchable colour from 2700K to 2900K is also discontinued - but you can still buy them as old stock from good lighting wholesalers.