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Metal-halide lamp behavior again

T

Travis Evans

Jan 1, 1970
0
This is largely meant to be a follow-up of I.N. Galidakis's first post
in the thread I started two months ago, which no longer appears to be on
my news server (or else I would have followed up normally).

Regarding argon flashes in HPM lamps--these would be reddish or
purplish in color, wouldn't they? Some time after the original thread I
had obtained a HPM fixture and think I saw some of these on about three
occasions so far during warmup (out of probably a couple hundred or so
starts). The first two were very weak reddish flashes which were so
brief and subtle I almost didn't notice them. A little earlier today it
happened a third time, but it was a bright, unmistakable purple flash
that lasted about half a second. The ballast hum even changed pitch
momentarily during this flash.

As far as funny behavior of Sodium in MH lamps goes--I wonder if this is
what happened on two occasions with my MH lamp (again, out of probably
around 200-300 starts or so) when instead of the usual dim grayish blue
glow immediately on switch-on I got a somewhat brighter, distinct
orangish white very much like the color from a typical incandescent
lamp. This lasted about 20-30 seconds or so before turning into the
usual clear-mercury-like color of mid-warmup and proceding through the
remainder of the warm-up period as normal. Sadly, it didn't occur to
me to grab my homemade “DVD-in-a-cardboard-box†spectroscope to check it
out before it was too late.

While I'm at it, I have a Lights of America S68 HPS lamp. I notice that
any time (I can always reproduce it) I turn it on when cold (i.e., full
warmup) and then turn it off again after only a couple of seconds, the
arc tube gives off an interesting faint blue-violet afterglow that lasts
for some time, sort of like the afterglow from high-persistence
phosphors. It seems to become less blue and more violet as it fades,
though that may just be me. If the lamp is on for longer than a several
seconds when switched off, I don't get any glow; if I leave it on longer
than this, I just get the usual orange-hot incandescent glow. Just
curious what this was. I found a couple of topics discussing similar
things but don't know if they are at all related:

http://groups.google.com/group/sci....read/thread/bddcb99278b34fcd/cd0211e46ebc0372

http://groups.google.com/group/sci....read/thread/5c0f030a9d4139e0/aa04a026c063acec
 
D

Don Klipstein

Jan 1, 1970
0
This is largely meant to be a follow-up of I.N. Galidakis's first post
in the thread I started two months ago, which no longer appears to be on
my news server (or else I would have followed up normally).

Regarding argon flashes in HPM lamps--these would be reddish or
purplish in color, wouldn't they? Some time after the original thread I
had obtained a HPM fixture and think I saw some of these on about three
occasions so far during warmup (out of probably a couple hundred or so
starts). The first two were very weak reddish flashes which were so
brief and subtle I almost didn't notice them. A little earlier today it
happened a third time, but it was a bright, unmistakable purple flash
that lasted about half a second. The ballast hum even changed pitch
momentarily during this flash.

As far as funny behavior of Sodium in MH lamps goes--I wonder if this is
what happened on two occasions with my MH lamp (again, out of probably
around 200-300 starts or so) when instead of the usual dim grayish blue
glow immediately on switch-on I got a somewhat brighter, distinct
orangish white very much like the color from a typical incandescent
lamp. This lasted about 20-30 seconds or so before turning into the
usual clear-mercury-like color of mid-warmup and proceding through the
remainder of the warm-up period as normal. Sadly, it didn't occur to
me to grab my homemade “DVD-in-a-cardboard-box†spectroscope to check it
out before it was too late.

I occaisionally see MH lamps in early warmup producing an impressive
amount of incandescent-like glow. I suspect the arc is terminating on the
tips of the electrodes at that point, which it normally does when the arc
tube is more warmed up. But in early warmup, the arc often terminates on
the radiators of the electrodes instead. When the arc terminates on the
electrode tips in early warmup when current is higher, the electrode tips
glow brightly. When the arc itself is dim, the incandescent electrode
tips can produce much of the light.

Meanwhile, as for reddish flashes in the arc: I somewhat remember
seeing a spectrum of one of those in progress, and doggone-it I don't
remember achieving an identification then - except it did not appear to me
to be argon. It could have been strontium and/or barium from the
electrode coating. More recently I have idetified barium and also a
mixture of strontium and barium in spectra of discolored glow adjacent to
electrodes.

I have also seen metal halide lamps flash during warmup when molten
halide moves from one location in the arc tube to another. I remember
seeing the spectrum of one of those in progress, and that was heavy on
sodium.

- Don Klipstein ([email protected])
 
T

TKM

Jan 1, 1970
0
Don Klipstein said:
I occaisionally see MH lamps in early warmup producing an impressive
amount of incandescent-like glow. I suspect the arc is terminating on the
tips of the electrodes at that point, which it normally does when the arc
tube is more warmed up. But in early warmup, the arc often terminates on
the radiators of the electrodes instead. When the arc terminates on the
electrode tips in early warmup when current is higher, the electrode tips
glow brightly. When the arc itself is dim, the incandescent electrode
tips can produce much of the light.

Meanwhile, as for reddish flashes in the arc: I somewhat remember
seeing a spectrum of one of those in progress, and doggone-it I don't
remember achieving an identification then - except it did not appear to me
to be argon. It could have been strontium and/or barium from the
electrode coating. More recently I have idetified barium and also a
mixture of strontium and barium in spectra of discolored glow adjacent to
electrodes.

I have also seen metal halide lamps flash during warmup when molten
halide moves from one location in the arc tube to another. I remember
seeing the spectrum of one of those in progress, and that was heavy on
sodium.

- Don Klipstein ([email protected])

From my experience with MH, Don is correct. The flashes in the arc during
warmup are from the halides and from whatever halide chemistry is active at
the instant of the flash.

Terry McGowan
 
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