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Metal-halide lamp behavior

T

Travis Evans

Jan 1, 1970
0
I recently started buying HID light fixtures to have fun with/use in my room
[yes, I'm crazy. :) My favorite part is the warm-up period!]. A few days
ago, I got a 100-watt MH fixture and just wanted to find out whether the
following behavior is normal, as this is my first "hands-on" experience
with a MH lamp.

After the first several "normal" starts, the lamp then developed a behavior
where it would flash a very bright red (sometimes startling me) a couple of
times for a fraction of a second just an instant before warm-up was
complete, then it would return to its normal color and operate normally.
This happened for the next few starts and then did not occur for the next
couple of starts.

Now, while ago, I just experienced a much more dramatic behavior. I wanted
to find out how long the lamp takes to restart when switched off and right
back on again, so I was power cycling it and recording the time until
restriking occurred. My plan was to do only three trials (I know that
starting causes wear). On the second trial, the very bright red color
appeared again just before the end of warm-up, but remained stable for a
whole 10-20 seconds or so! I think it may have gradually faded to a very
incandescent-lamp-like orangish color, then after a few more moments jumped
to a yellowish-white. Now I think the lamp is closer to its normal white
color, except I think it seems a tiny bit more yellow than usual.

I know that it's normal for MH lamps to slowly shift colors over their
lives, but I haven't heard anything about sudden changes, particularly
during warm-up and with a brand-new lamp. Just wanted to know what this
group's thoughts were about this. Is it okay, or should I stop messing
with it before it explodes on me? :) (Actually, it is an open-fixture
rated lamp, though.)
 
T

TKM

Jan 1, 1970
0
Travis Evans said:
I recently started buying HID light fixtures to have fun with/use in my
room
[yes, I'm crazy. :) My favorite part is the warm-up period!]. A few days
ago, I got a 100-watt MH fixture and just wanted to find out whether the
following behavior is normal, as this is my first "hands-on" experience
with a MH lamp.

After the first several "normal" starts, the lamp then developed a
behavior
where it would flash a very bright red (sometimes startling me) a couple
of
times for a fraction of a second just an instant before warm-up was
complete, then it would return to its normal color and operate normally.
This happened for the next few starts and then did not occur for the next
couple of starts.

Now, while ago, I just experienced a much more dramatic behavior. I
wanted
to find out how long the lamp takes to restart when switched off and right
back on again, so I was power cycling it and recording the time until
restriking occurred. My plan was to do only three trials (I know that
starting causes wear). On the second trial, the very bright red color
appeared again just before the end of warm-up, but remained stable for a
whole 10-20 seconds or so! I think it may have gradually faded to a very
incandescent-lamp-like orangish color, then after a few more moments
jumped
to a yellowish-white. Now I think the lamp is closer to its normal white
color, except I think it seems a tiny bit more yellow than usual.

I know that it's normal for MH lamps to slowly shift colors over their
lives, but I haven't heard anything about sudden changes, particularly
during warm-up and with a brand-new lamp. Just wanted to know what this
group's thoughts were about this. Is it okay, or should I stop messing
with it before it explodes on me? :) (Actually, it is an open-fixture
rated lamp, though.)

The flashing behavior during warm-up is normal for metal halide lamps. Some
of the halides are in liquid form during warm-up process and so blobs of
material enter the arc stream randomly and cause the flash as they vaporize
and contribute to the light output. It's also part of the lamp
stabilization process as the mercury, sodium and halides all seek to find
their best operating temperature points within the arc tube.

Once the lamp has operated for some hours without being physically
disturbed, you can start the process over by simply rotating the lamp or
tipping it slightly. Do that when the lamp is off and you'll likely have a
new light show when you turn it on again.

Terry McGowan
 
T

Travis Evans

Jan 1, 1970
0
I.N. Galidakis said:
If you could tell me exactly the lamp type, I could give you more details.

The ANSI designation is M90/O.
 
T

Travis Evans

Jan 1, 1970
0
TKM said:
Once the lamp has operated for some hours without being physically
disturbed, you can start the process over by simply rotating the lamp or
tipping it slightly. Do that when the lamp is off and you'll likely have
a new light show when you turn it on again.

Do you mean move the lamp and then place it back in its original orientation
before turning it on or turning it back on in that slightly different
orientation?
 
T

TKM

Jan 1, 1970
0
Travis Evans said:
Do you mean move the lamp and then place it back in its original
orientation
before turning it on or turning it back on in that slightly different
orientation?

It should end up in a different position. That way when the lamp is turned
on and goes through the warm-up process, the "pool" of halides will move,
drip and slide around to different optimum temperature points. As the
halides move, you'll get the light show. I'll guess that the maximum
movement of halides will happen if the arc tube ends up 180 degrees from
where it started.

Terry McGowan
 
C

Chris Carlen

Jan 1, 1970
0
Travis said:
I recently started buying HID light fixtures to have fun with/use in my room
[yes, I'm crazy. :)

You are not alone. I played with mercury and sodium arcs while a kid,
and now I'm into MH for good white light. My favorite are Philips
MasterColor ceramic MH. Haven't devised a permanent indoor installation
yet though.



--
Good day!

____________________________________
CRC
[email protected]
NOTE, delete texts: "REMOVETHIS" and
"BOGUS" from email address to reply.
 
T

Travis Evans

Jan 1, 1970
0
Chris said:
Travis said:
I recently started buying HID light fixtures to have fun with/use in my
room
[yes, I'm crazy. :)

You are not alone. I played with mercury and sodium arcs while a kid,
and now I'm into MH for good white light. My favorite are Philips
MasterColor ceramic MH. Haven't devised a permanent indoor installation
yet though.

I know of some on this newsgroup (judging from past posts) who are the same
way, so it's nice to have some of my own. I would have gotten started with
this ages ago if I had known how inexpensive some basic HID fixtures are at
home centers! I have a 50-watt HPS also and plan on adding a 100-watt HPM
to my collection soon.

My installations could probably be described as "semi-permanent". The HPS
one hangs on a nail (the whole fixture is just a lightweight plastic thing)
so I can easily move it to another location if I want to, but I mostly keep
it near the head of my bed since it makes a nice reading light. :) The
MH one had to be screwed into the wall, though, so that one probably won't
be going anywhere anytime soon. They're intended to be outdoor fixtures,
but we wired them to wall plugs with inline switches, and I just cover the
photocells as necessary to make them stay on. One of my initial concerns
was whether the heat output would be low enough for safe indoor use, but
heat doesn't seem any worse with either fixture than it would with ordinary
indoor lighting fixtures.
 
T

Travis Evans

Jan 1, 1970
0
TKM said:
It should end up in a different position. That way when the lamp is
turned on and goes through the warm-up process, the "pool" of halides will
move,
drip and slide around to different optimum temperature points. As the
halides move, you'll get the light show. I'll guess that the maximum
movement of halides will happen if the arc tube ends up 180 degrees from
where it started.

I'm not able to change the vertical position of the lamp due of the fixture
installation and because of the note printed on the lamp box that states
that the lamp is only to be operated base-up, but I've tried rotating the
lamp in the socket slightly. That didn't seem to make much difference.

On the other hand, it seems that if I power cycle the lamp and let the
ballast sit there trying to hot-restrike it, I quite often get a light show
when the lamp finally restrikes around 4.5 minutes later, and sometimes
during the next couple of cold starts after that. I don't plan on making a
habit of doing that, though.
 
T

TKM

Jan 1, 1970
0
Travis Evans said:
I'm not able to change the vertical position of the lamp due of the
fixture
installation and because of the note printed on the lamp box that states
that the lamp is only to be operated base-up, but I've tried rotating the
lamp in the socket slightly. That didn't seem to make much difference.

On the other hand, it seems that if I power cycle the lamp and let the
ballast sit there trying to hot-restrike it, I quite often get a light
show
when the lamp finally restrikes around 4.5 minutes later, and sometimes
during the next couple of cold starts after that. I don't plan on making
a
habit of doing that, though.

Thanks for the clarification. Somehow, I had thought that the lamp was
off-vertical.

You are not hurting the lamp significantly by going through hot restrikes.
When the lamp is turned off while hot, the halides are in solid, liquid and
gaseous form and changing states as the lamp cools. The gas currents and
field forces inside the arc tube move the materials around a bit so that
when the arc restrikes there are blobs of materials that suddenly ionize and
start emitting light -- the light show. You can influence the show somewhat
by moving a strong permanent magnet around the lamp as it operates. That
will force the arc to move inside the arc tube and change the temperature
distribution of the halides.

Threre is some risk of overheating the arc tube when you move the arc with
the magnet and the tube could crack or shatter; but i believe you said that
you have a protected MH lamp with an innter shield around the arc tube. Of
course, you may not want to risk your lamp either.

Terry McGowan
 
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