Don Klipstein wrote:
[snip]
There are other differences among lamps, which are minor as far as I
know. The most significant of these appears to me to be the wattage.
There is also the issue of retrofit HPS. If I recall right, regular HPS
lamps contain xenon as buffer gas and a sodium-mercury amalgam.
Retrofit HPS lamps which are designed to run on HPM circuits contain neon
as a buffer gas
Specifically, the common neon-argon mixture of 99.5% neon .5% argon.
This is used in "standard intensity" neon glow lamps such as NE-2, while
"high intensity" neon glow lamps such as NE-2H and most truly neon signs
have pure neon.
The Ne-Ar mixture has a main glow discharge column glowing a slightly
pinkish or "strontium-like" orangish-pinkish red in normal HPS starting
duty.
At reduced currents, the color shifts to more purplish. At 1 milliamp
(very far from normal usage), the main discharge column has a more
argon-like color close to lavendar - and the ends of the arc tube glow
with the very different orange color of cathode/negative glow of a glow
discharge in this gas mixture. This orange color is like that of "true
Ne-2" lamps, appearing slightly yellowish in comparison to the purplish
glow of the main discharge column. At one time I thought this was sodium
glow, until I tried a diffraction grating and found it was neon. The
sodium-similar-color yellow line of neon is strong here.
I even used a diffraction grating to view a hot (recently used normally)
retrofit HPS lamp operated at 1 mA as it cooled. At some time, I saw the
585.25 nm neon line (and other neon lines) fade in, followed by the
589/589.6 nm sodium lines fading out. The yellowish orange end glow of a
retrofit HPS lamp operated at 1 milliamp is from neon in the neon-argon
mixture, even though the main discharge column glows with a more argon-like
color at such low current.
and have a starting electrode wound around the alumina discharge tube
which initiates the discharge through a neon glow discharge, so their
starting behavior is quite different from that of regular HPS lamps.
When they start, they glow red, from neon, until sodium kicks in.
I think retrofit HPS lamps also contain a mercury-sodium amalgam, so
"eventually" their behavior near end of life should be asymptotically
similar to that of regular HPS lamps, although I've never seen an aged
retrofit HPS.
I have seen many retrofit HPS lamps in USA. I even have a few aged
ones.
In my experience, these usually have even more mercury than non-retrofit
HPS lamps have. They require even higher voltage drop than non-retrofit
HPS 200-400W and higher-voltage 150W (S56). At times I have even seen
some retrofit HPS lamps in new condition change from red to a mercury-like
color as they started to warm up.
These were popular in the States when I was there. We don't have them
here in Eu.
My experience is from the States. It appears to me that the popularity
of retrofit HPS lamps (mostly H39 and H33 ballast compatibility) has been
decreasing somewhat as the decades go by, in favor of S56 and S51.