I noticed at dusk when a group of HPS lamps starts up at the same time, some come on at a low brightness to a dim dark orange color, and some come on to a bluish mercury color before warming up. Why is this? It seems like cyclers usually do a bluish startup, so maybe it has to do with the age of the lamp?
Oddly, it seems to always be one or the other, no in between.

Also there is an area with 9 HPS post lights near me, and they never cycle for more than a week or so at EOL (sometimes not at all), they just flicker randomly for a while and then continuously glow a very dim orange color. Is this a different type of starter or something that causes this EOL behavior?

Thanks

I noticed the HPS NEMA heads here usually do glow a bit blue at startup, so I think it does have to do with age. But my Regent area light seems to be brand new and the lamp on that too glows blue at startup, so I'm not sure if it has to be a bulb with a lot of use to do it.

Also, I notice some of the HPS cobras here glow blue all the time when they go EOL. They look a lot like MV if you didn't know better.

Old or cycling HPS lamps, run-up more bluish than new HPS lamps. But non-cycling HPS lamps always run-up bluish even when new.

I noticed the HPS NEMA heads here usually do glow a bit blue at startup, so I think it does have to do with age. But my Regent area light seems to be brand new and the lamp on that too glows blue at startup, so I'm not sure if it has to be a bulb with a lot of use to do it.

Also, I notice some of the HPS cobras here glow blue all the time when they go EOL. They look a lot like MV if you didn't know better.

That's interesting. I rarely see that with HPS here, if anything, it glows dim orange at EOL.

Old or cycling HPS lamps, run-up more bluish than new HPS lamps. But non-cycling HPS lamps always run-up bluish even when new.

So they all start blue, but the older the lamp, the longer it stays bluish?
I wounder what changes in the arc tube cause this. I'd think it would do the opposite.
AFAIK, a lamp cycles when the arc tube pressure gets too high and the ballast can't provide enough current. If the old lamps start more bluish, doesn't that mean the arc tube pressure is lower?

The lamp cycle when the its voltage rise beyond the limit of the ballast.
With regular HPS lamps, the lamp run-up bluish only when old or cycling. But non-cycling HPS lamps (The ones that lights mercury color at EOL), always starts bluish even when new, and retains their color until the last sodium has been consumed.
HPS lamps can glow dim LPS color if the outer bulb lost vacuum, or if the arctube leaks.

The lamp cycle when the its voltage rise beyond the limit of the ballast.
With regular HPS lamps, the lamp run-up bluish only when old or cycling. But non-cycling HPS lamps (The ones that lights mercury color at EOL), always starts bluish even when new, and retains their color until the last sodium has been consumed.
HPS lamps can glow dim LPS color if the outer bulb lost vacuum, or if the arctube leaks.

Cool, that makes sense, thanks! I never heard of non-cycling lamps before. Thought ballasts could be non-cycling though.

I know a restaurant that converted their parking lot to LED a few years ago, and a lone HPS floodlight got left behind on one of the poles. I timed it years ago and it was about 2 minutes per cycle. Now it's around 50 seconds per cycle, but amazingly still working after YEARS!

The streetlight infront of my place has an EOL HPS lamp and it has been burning a steady mercury vapour colour for many years now. Lamp is about 8 years old and lost its sodium colour after about 2 years. It quickly went from orange to pink to white and eventually to mv colour in a matter of months. It still lights up reliably each night and doesn't cycle.

The streetlight infront of my place has an EOL HPS lamp and it has been burning a steady mercury vapour colour for many years now. Lamp is about 8 years old and lost its sodium colour after about 2 years. It quickly went from orange to pink to white and eventually to mv colour in a matter of months. It still lights up reliably each night and doesn't cycle.

I've seen similar occurrences. It is quite nice.

I've seen only very few cases here in Israel, where HPS changes to bluish mercury color without cycling like at the heart of Shprinzak neighborhood: https://www.lighting-gallery.net/gallery/displayimage.php?pos=-144825 , But these weren't unsaturated HPS lamps.
The majority of HPS lamps I've seen here, that don't reaching sodium color, always cycles: https://www.lighting-gallery.net/gallery/displayimage.php?pos=-147749