I see more ecological HPS lamps (No-Mercury lamps), but are they really ecological? What is the impact of the sodium in environment? Are they junkie  or better? 

They indeed don't have any mercury in them, just sodium and xenon I believe as a buffer gas.

sodium turns to sodium hydroxide in the environment because it is highly reactive.

Those no mercury sodium lamps are junk especaly the ones Philips makes! The don't last long at all and they cycle a lot!! I know this because my family owns a huge printing company with 30 fixtures with 400W Philips no mercury ones!! Sylvania makes good no mercury HPS Lamps!

Yeah current Philips HPS lamps tend to be junk although they are US made and all...

Mercury is used for maintain good electric properties of the arc and make a better start. It's normal no-mercury ones cycles faster... BTW, is the sodium hydroxide dangerous or toxic? 

Just as a sidebar of sorts, and I'm on record here as being a lover of all things old- lamps included, I sell Philips lamps for a living and the return rate on the HPS Alto lamps has been next to nothing. Really. We sell several hundred monthly, and I haven't had a return since late October, and when I brought that lamp home, it worked. The MH are a bit more temperamental, and we do get a few a month occasionally. But the ALTO stuff really is okay, at least up here in PA!!!!

Its also known as lye.