mercury lights

[hungry1]

Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? It doesn't do it
consistantly, but rather often.
Thanks,

 

[Sam Goldwasser]

Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? It doesn't do it
consistantly, but rather often.

1. Bad lamp.
2. Bad ballast.
3. Bad wiring.
4. If solar activated, photodetector being fooled by stray light or
someone messing with it using a flashlight or laser pointer.

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[NSM]

| Could someone tell me what might be the cause of a mercury vapor light to
| intermittantly go off and in a few minutes come back on? It doesn't do it
| consistantly, but rather often.
| Thanks,

End of life for the lamp.

N

 

[Fred McKenzie]

<< Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? >>

Curt-

To add to Sam Goldwasser's comments, it is possible that a very short glitch in
the AC power, is causing the light to go out. Once it is out, it has to warm
up before it comes back on. I think a good lamp would have the ability to
withstand a short outage without having to heat-up again.

Perhaps this is due to a defective lamp or one that is getting old. Has it
always done this, or just started after several years of service?

If it has always done it, could you have the wrong wattage lamp for the
fixture? I think the ballast has to be matched to the bulb, just as with
flourescent lamps.

Fred

 

[Sam Goldwasser]

<< Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? >>

Curt-

To add to Sam Goldwasser's comments, it is possible that a very short glitch in
the AC power, is causing the light to go out. Once it is out, it has to warm
up before it comes back on. I think a good lamp would have the ability to
withstand a short outage without having to heat-up again.

I don't think it is so much a function of the lamp as of the ballast.

Perhaps this is due to a defective lamp or one that is getting old. Has it
always done this, or just started after several years of service?

Could be, certainly the first thing to try by replacing the lamp.

But once that cycling begins, an end-of-life lamp would likely continue to
do it continuously, not at random.

If it has always done it, could you have the wrong wattage lamp for the
fixture? I think the ballast has to be matched to the bulb, just as with
flourescent lamps.

Yep.

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Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

 

[James Sweet]

Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? It doesn't do it
consistantly, but rather often.
Thanks,

Mercury lamps rarely do this, but I have seen some of the cheap Chinese made
lamps cycle when they reach end of life. A guy I know had a 100W one that
only lasted 3 months, sure a big step down from some of the 60's vintage
Westinghouse and GE lamps that happily ran for 20-30 years.

Most HPS lamps will cycle when they age and the emissive material wears off
the cathodes, Metal Halide lamps will often suffer an arc tube rupture
before this happens, in lighting industry terms a "non-passive" failure but
what it usually comes down to is a shower of red hot quartz shards and
broken glass. This is why it's important to always have the cover in place
when operating these lamps.

 

[James Sweet]

If it has always done it, could you have the wrong wattage lamp for the
fixture? I think the ballast has to be matched to the bulb, just as with
flourescent lamps.

Yes it does, mercury lamps are quite tolerant of over and under wattage
operation compared to other discharge lamps, but in either case lamp life
suffers, sometimes dramatically. If the cathodes are too hot they evaporate
and blacken the arc tube, if they're too cold they sputter and blacken the
tube, either way the lamp lumens depreciate substantially over time while
power consumption remains the same.

 

[Jerry G.]

Most of the time this is a sign of the lamp failing. Sometimes it is also
the ballast transformer as well. You will have to try the lamp first. If the
lamp is still flickering, then change the ballast transformer.

--

Jerry G.
======


Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? It doesn't do it
consistantly, but rather often.
Thanks,

 

[NSM]

| Most of the time this is a sign of the lamp failing. Sometimes it is also
| the ballast transformer as well. You will have to try the lamp first. If
the
| lamp is still flickering, then change the ballast transformer.

Change the ignitor first. It's easier and cheaper than changing the ballast
transformer. That you should be able to test by shorting it with an AC
ammeter with the ignitor removed.

N

 

[James Sweet]

| Most of the time this is a sign of the lamp failing. Sometimes it is also
| the ballast transformer as well. You will have to try the lamp first. If
the
| lamp is still flickering, then change the ballast transformer.

Change the ignitor first. It's easier and cheaper than changing the ballast
transformer. That you should be able to test by shorting it with an AC
ammeter with the ignitor removed.

N

This is a mercury lamp, they don't use igniters. Only HPS, modern
pulse-start metal halide and some modern LPS lights use an igniter. Mercury
vapor lamps are all probe-start and rely only on sufficient open circuit
voltage from the ballast.

Also his lamp is igniting so even if it did use an igniter that's not the
problem, if the igniter fails in a pulse-start fixture the lamp will never
light.

 

[NSM]

| This is a mercury lamp, they don't use igniters. Only HPS, modern
| pulse-start metal halide and some modern LPS lights use an igniter.
Mercury
| vapor lamps are all probe-start and rely only on sufficient open circuit
| voltage from the ballast.
|
| Also his lamp is igniting so even if it did use an igniter that's not the
| problem, if the igniter fails in a pulse-start fixture the lamp will never
| light.

He may have mis-identified the lamp type.

N

 

[James Sweet]

| This is a mercury lamp, they don't use igniters. Only HPS, modern
| pulse-start metal halide and some modern LPS lights use an igniter.
Mercury
| vapor lamps are all probe-start and rely only on sufficient open circuit
| voltage from the ballast.
|
| Also his lamp is igniting so even if it did use an igniter that's not the
| problem, if the igniter fails in a pulse-start fixture the lamp will never
| light.

He may have mis-identified the lamp type.

Entirely possible, though that still doesn't change the fact that the
igniter is apparently not the problem in this particular case.

That is a good point though, the two common types of sodium lights are
pretty distinctive, but people very regularly misidentify metal halide
lights as mercury. A probe start MH lamp will usually light up fine on a
mercury ballast but fail within a couple months. The other way around is
acceptable for 175W and larger sizes though.

 

[Bill Jeffrey]

Could someone tell me what might be the cause of a mercury vapor light to
intermittantly go off and in a few minutes come back on? It doesn't do it
consistantly, but rather often.
Thanks,

Is it possible that the fixture has an overheat switch in it? Many
household recessed incandescent fixtures have such a switch, and they
sometimes cycle annoyingly (though safely!)

Bill Jeffrey

 

[[email protected]]

Mercury vapour lights use a gas such as neon to strike a
running current limited arc, the lamp starts to heat up,
vaporizing the mercury (which at low temps may be solid -
mercury theremometers can freeze you know), the
temperature and pressure in the bulb rises as the
mercury vapour carries the current. If the pressure rises
too high for the mains supply to sustain the arc, the
arc extinguishes and the lamp has to cool before
it will re-start. Then it does the above cycle again.
This repeating cycle usually means a defective or
worn out lamp. High pressure lighting mercury
vapour lamps (in the UK 240v supply) run off the
mains through a current limiting choke, regulating
the current to 2A or so. Not sure about the lower
voltage US mains, they may need some special
arrangement to get the arc started.

Low pressure mercury vapour tubes (not used
for lighting) strike at 1KV or so, and run at
typically 100mA from a current limiting transformer
called a leak transformer. Leak because some
of the primary flux is leaked away through a
shunt so as to limit the current. Making it
a constant (well near enough) current, high
voltage transformer.

 

[NSM]

| Entirely possible, though that still doesn't change the fact that the
| igniter is apparently not the problem in this particular case.
|
| That is a good point though, the two common types of sodium lights are
| pretty distinctive, but people very regularly misidentify metal halide
| lights as mercury. A probe start MH lamp will usually light up fine on a
| mercury ballast but fail within a couple months. The other way around is
| acceptable for 175W and larger sizes though.

No replies from the OP so at this point speculation is moot???

FWIW, I always try the easy things first. The other way around tends to lead
to much vigorous cursing!

N

 

[James Sweet]

Mercury vapour lights use a gas such as neon to strike a
running current limited arc, the lamp starts to heat up,
vaporizing the mercury (which at low temps may be solid -
mercury theremometers can freeze you know), the
temperature and pressure in the bulb rises as the
mercury vapour carries the current. If the pressure rises
too high for the mains supply to sustain the arc, the
arc extinguishes and the lamp has to cool before
it will re-start. Then it does the above cycle again.
This repeating cycle usually means a defective or
worn out lamp. High pressure lighting mercury
vapour lamps (in the UK 240v supply) run off the
mains through a current limiting choke, regulating
the current to 2A or so. Not sure about the lower
voltage US mains, they may need some special
arrangement to get the arc started.

Mercury lamps use argon as the fill gas, and for 120v operation they use an
autotransformer ballast just like large (700-1000W) require to run on 240v
mains.

Low pressure mercury vapour tubes (not used
for lighting) strike at 1KV or so, and run at
typically 100mA from a current limiting transformer
called a leak transformer. Leak because some
of the primary flux is leaked away through a
shunt so as to limit the current. Making it
a constant (well near enough) current, high
voltage transformer.

SOX (low pressure sodium) lamps use a similar type of transformer, this is
why while the lamp efficiency is very high, the system efficiency is rather
pathetic for the smaller sizes (15W ballast loss for an 18W lamp!) . Some
modern units use electronic ballasts which are more efficient, I'm not sure
how much more though.

 

[hungry1]

More info on lamp...it's in venezuela with 120v same setup as US. (well
almost). It is a 175W lamp (like a street light) mounter on a pole near the
street. It is about 2yrs.old. The light is more green than anything I can
describe. (we do have some of themore yellowish lights in some areas, but I
think they are sodium).There are some night that the light stays on all
night, and yet some nights, it stays on about 10-15 minutes and goes off for
2-3 minutes then back on again....Then maybe it's 2 hrs before it goes off
again... or maybe it stays on the rest of the night.
Thanks for all of you input.

 

[NSM]

| More info on lamp...it's in venezuela with 120v same setup as US. (well
| almost). It is a 175W lamp (like a street light) mounter on a pole near
the
| street. It is about 2yrs.old. The light is more green than anything I can
| describe. (we do have some of themore yellowish lights in some areas, but
I
| think they are sodium).There are some night that the light stays on all
| night, and yet some nights, it stays on about 10-15 minutes and goes off
for
| 2-3 minutes then back on again....Then maybe it's 2 hrs before it goes off
| again... or maybe it stays on the rest of the night.
| Thanks for all of you input.

Up here a .22 will usually ensure prompt repair.

N

 

[hungry1]

Very true....but I own this one and I'm the one that has to pay for the
repairs!

 

[James Sweet]

More info on lamp...it's in venezuela with 120v same setup as US. (well
almost). It is a 175W lamp (like a street light) mounter on a pole near the
street. It is about 2yrs.old. The light is more green than anything I can
describe. (we do have some of themore yellowish lights in some areas, but I
think they are sodium).There are some night that the light stays on all
night, and yet some nights, it stays on about 10-15 minutes and goes off for
2-3 minutes then back on again....Then maybe it's 2 hrs before it goes off
again... or maybe it stays on the rest of the night.
Thanks for all of you input.

Sounds like mercury, they do tend to turn a bit more greenish as the lamps
age. Look at the arc tube, if it's blackened then the lamp is shot for sure.
Replacement bulbs are inexpensive and should be readily available.