[Richard]

I've got a streetlamp fitting. There is a "u" tube in the middle of the lamp
and that glows brightly, because I can see that when I look end on to the
lamp. The outer envelope curiously is covered dark, so that the light from
the inner "u" tube does not shine through very much . I cannot understand
this, because it does not look like there is a lamp defect, but the lamp is
quite dull. Is there a defect? TIA.

 

[Victor Roberts]

I've got a streetlamp fitting. There is a "u" tube in the middle of the lamp
and that glows brightly, because I can see that when I look end on to the
lamp. The outer envelope curiously is covered dark, so that the light from
the inner "u" tube does not shine through very much . I cannot understand
this, because it does not look like there is a lamp defect, but the lamp is
quite dull. Is there a defect? TIA.

LPS lamps have a tin oxide coating on the outside to trap
and conserve heat. It is possible that the costing has
become damaged with age.

Since you use low pressure sodium in the subject line, I
assume that the color of what little light you do get is
consistent with low pressure sodium.


--
Vic Roberts
http://www.RobertsResearchInc.com
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[Andrew Gabriel]

LPS lamps have a tin oxide coating on the outside to trap
and conserve heat. It is possible that the costing has
become damaged with age.

Since you use low pressure sodium in the subject line, I
assume that the color of what little light you do get is
consistent with low pressure sodium.

It might be that the inner tube has become punctured,
which results in sodium being sucked into the outer
bulb vacuum where it condenses into a mirror finish
obscuring the glass. This is a very common failure
mode for LPS lamps. It happens when the internal
protective coating on the inner tube eventually breaks
down, letting the highly reactive sodium vapour contact
the glass which it rapidly corrodes through. The arc tube
will often continue working fine for some time in spite
loss of some of the sodium, but little light escapes
through the outer bulb, although it usually isn't
obscured over the whole lamp.

 

[Richard]

It might be that the inner tube has become punctured,
which results in sodium being sucked into the outer
bulb vacuum where it condenses into a mirror finish
obscuring the glass. This is a very common failure
mode for LPS lamps. It happens when the internal
protective coating on the inner tube eventually breaks
down, letting the highly reactive sodium vapour contact
the glass which it rapidly corrodes through. The arc tube
will often continue working fine for some time in spite
loss of some of the sodium, but little light escapes
through the outer bulb, although it usually isn't
obscured over the whole lamp.

Yes, I belive you are correct.

There is some movement inside when I shake the lamp. You would not
physically see anything as defective, the dark obscuration is not irregular,
it looks like the lamp was made that way, like the outer tube it has been
sprayed with a dark covering. All the outer tube is coloured dark in this
case. Light output is low, but the inner "u" tube glows bright orange.

 

[TKM]

Yes, I belive you are correct.

There is some movement inside when I shake the lamp. You would not
physically see anything as defective, the dark obscuration is not
irregular, it looks like the lamp was made that way, like the outer tube
it has been sprayed with a dark covering. All the outer tube is coloured
dark in this case. Light output is low, but the inner "u" tube glows
bright orange.

Yes, you and Andrew have diagnosed the problem and the lamp has failed --
or, more properly, turned into a "red burner" where the neon starting gas is
producing most of the light since there's little sodium left in the arc tube
to do that.

Terry McGowan

 

[Victor Roberts]

It might be that the inner tube has become punctured,
which results in sodium being sucked into the outer
bulb vacuum where it condenses into a mirror finish
obscuring the glass. This is a very common failure
mode for LPS lamps. It happens when the internal
protective coating on the inner tube eventually breaks
down, letting the highly reactive sodium vapour contact
the glass which it rapidly corrodes through. The arc tube
will often continue working fine for some time in spite
loss of some of the sodium, but little light escapes
through the outer bulb, although it usually isn't
obscured over the whole lamp.

Andrew,

You analysis seems to be correct. We use very few LPS
lamps in the US and I have little experience with them since
the organizations I have worked for have never tried to
develop an improved version.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

 

[Victor Roberts]

On Mon, 21 Jan 2008 23:03:12 -0800 (PST),

I've seen it in just three places over there; an 18W wall mounted lamp
outside a cinema in New York, High-Wattage ones under the bridge which
crosses the road outside Grand Central Terminal, also in New York, and
at the closed station, Franklin Square I think it was called, on PATCO
in Philadelphia.

I can add a few more places. They were used on the Long
Island Expressway or one of the other Long Island highways
when I was a kid. That was many, many years ago. Until
recently they were used in the parking lot of a New York
State Highway Department location near the New York Thruway
in the Albany, NY area. And, shortly after Osram bought
Sylvania they appeared for a short time on the Massachusetts
Turnpike. We thought that the Osram ownership of a
Massachusetts company might have triggered that but it also
could have been the Philips presence in the US after their
purchase of Westinghouse lighting, or none of the above.

I wonder why it wasn't more widely used over there;
it can't be that non-white light was not acceptable, because SON lamps
are very widely used.

This part is easy We don't use the highest efficacy
light source for the same reason that we live in oversize
houses, drive big, gas guzzling cars (more like trucks) and
don't have decent public transportation systems unless we
happen to live in one of the big cities. We think we are so
rich that we don't have to make compromises - and we see
where that has gotten us.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

 

[Paul M. Eldridge]

.... We used to have a strange lantern, it was a sort of rectangular
disk, think of something the shape of an inverted photographic
developing dish, with two 180W SOX lamps, mounted along the long
sides, with the gear mounted between them. These lanterns ware most
often seen suspended from catenary along the centre of roads. When I
went to Sheffield by coach last May there were still some along the M1
motorway. I've also seen these strange lanterns, grouped in fours,
used for high-mast lighting; eight 180W SOX lamps is a lot of light!

There is, if it still exists, a mid roadway, high mast, cable
suspension system like you describe on one of the major autoroutes
outside Montréal, and it has to be one of the most comfortable
lighting systems I've ever experienced. Personal taste such as it is,
I much prefer this type of arrangement over the typical SON systems we
find almost everywhere.

I understand why high CCT and CRI light sources would be desirable in
urban environments, and in particular areas with high pedestrian
traffic, but on major roadways, LPS allows me to "filter out" some of
the visual distraction and concentrate on the task at hand. On the
other hand, I often wonder if my depth perception isn't somewhat
impaired. Are there any studies out there that would suggest this
last point is, in fact, a valid concern?

Cheers,
Paul

 

[Paul M. Eldridge]

Paul M. Eldridge wrote:
[snip]

I understand why high CCT and CRI light sources would be desirable in
urban environments, and in particular areas with high pedestrian
traffic, but on major roadways, LPS allows me to "filter out" some of
the visual distraction and concentrate on the task at hand. On the
other hand, I often wonder if my depth perception isn't somewhat
impaired. Are there any studies out there that would suggest this
last point is, in fact, a valid concern?

I think I may have reposted this reference long time ago, but just in case you
missed it:

Quoting from K.D. Alexopoulos, General Physics, Optics, First Edition, Athens
1966, page 133: (translation from Greek mine)

"...Although of very high efficiency, they are not often used for lighting,
because the yellow light they emit may be considered "unpleasant" and does not
render colors accurately. However, they are used in some cases (such as for the
lighting of highways, rural roads, ship docks, train crossings, etc), first
because the emitted light penetrates fog without being scattered significantly,
second because the eye adjusts better under monochromatic light and vision
becomes sharper..."

FWIW, my own experiments with an LPS lamp long time ago seem to support the last
part.

Hi Ioannis,

No, I hadn't caught that reference; thanks for reposting it again. In
general, I tend to believe night vision is improved, but on the matter
of depth perception I'm not so sure. I'm not a road engineer (nor do
I play one on TV), but I wonder if our response times in relation to
fast moving objects are not impaired.

And having spent most of my years here on the east coast, where rain,
snow and fog are a routine part of daily life [individually and
collectively], there's no doubt in my mind LPS is the better performer
under these conditions.

Now, on a totally unrelated note, as you may recall, I lost Kelsey
this past March. Well, after almost a year in passing, I'm pleased to
report there's another pair of puppy paws to join a long string of
male, sable collies that have graced my life.... Casey, Kyle,
Kingston, Kelsey and, now, Cameron. You can find his picture here:

http://www.freewebs.com/eastleigh/puppies.htm

Cheers,
Paul

 

[Paul M. Eldridge]

... They look so cute I wish I had a couple. If I had a farm, I would have 3
donkeys, 10 dogs, 30 cats, a dozen turkeys and 10 dozen chickens. I LOVE
chickens.

<chuckle> I haven't spent much time around chickens... well, dare I
say it, live ones... and if you ever have the opportunity to visit
this part of world and we can arrange to meet for dinner, I promise,
it won't be here!

http://www.swisschalet.com/home.php

Err, perhaps I better redirect you here:

Cheers,
Paul

 

[TKM]

There is, if it still exists, a mid roadway, high mast, cable
suspension system like you describe on one of the major autoroutes
outside Montréal, and it has to be one of the most comfortable
lighting systems I've ever experienced. Personal taste such as it is,
I much prefer this type of arrangement over the typical SON systems we
find almost everywhere.

I understand why high CCT and CRI light sources would be desirable in
urban environments, and in particular areas with high pedestrian
traffic, but on major roadways, LPS allows me to "filter out" some of
the visual distraction and concentrate on the task at hand. On the
other hand, I often wonder if my depth perception isn't somewhat
impaired. Are there any studies out there that would suggest this
last point is, in fact, a valid concern?

Cheers,
Paul

Years ago, some colleagues and I compared the visibility characteristics of
LPS, HPS and phosphor-coated mercury in a roadway lighting situation. We
matched luminances on various gray and neutral-colored objects and then
measured the visibility of those objects with a visibility meter. There was
little difference among the lamps as far as the overall visibility of the
objects was concerned; but we did notice that, under LPS lighting, visual
acuity (ability to see details) was somewhat better. That makes sense, of
course, since LPS is almost monochromatic and so produces less chromatic
aberration in the eye than the other sources. We didn't note any depth
perception effects.

Terry McGowan

 

[TKM]

Paul M. Eldridge wrote:
[snip]

I understand why high CCT and CRI light sources would be desirable in
urban environments, and in particular areas with high pedestrian
traffic, but on major roadways, LPS allows me to "filter out" some of
the visual distraction and concentrate on the task at hand. On the
other hand, I often wonder if my depth perception isn't somewhat
impaired. Are there any studies out there that would suggest this
last point is, in fact, a valid concern?

I think I may have reposted this reference long time ago, but just in case
you
missed it:

Quoting from K.D. Alexopoulos, General Physics, Optics, First Edition,
Athens
1966, page 133: (translation from Greek mine)

"...Although of very high efficiency, they are not often used for
lighting,
because the yellow light they emit may be considered "unpleasant" and does
not
render colors accurately. However, they are used in some cases (such as
for the
lighting of highways, rural roads, ship docks, train crossings, etc),
first
because the emitted light penetrates fog without being scattered
significantly,
second because the eye adjusts better under monochromatic light and vision
becomes sharper..."

FWIW, my own experiments with an LPS lamp long time ago seem to support
the last
part.

Cheers,
Paul

I've heard about LPS and improved visibility in fog for a long time; but
confirming data are elusive (although opinions are not ). Fog, being
white, scatters all colors equally; so why should yellow light somehow
scatter less? As a reference, I go back to a book entitled, Vision and
Highway Safety by M.J. Allen. (He was a professor of optometry at Indiana
University). He claims from his studies that using yellow automotive fog
lights, or indeed any color of light makes no difference in fog.

I wonder if the eye is being fooled by the improved visual acuity under LPS
lighting to be misled into thinking that vision is also improved.

Terry McGowan

 

[Don Klipstein]

Paul M. Eldridge wrote:
[snip]

I understand why high CCT and CRI light sources would be desirable in
urban environments, and in particular areas with high pedestrian
traffic, but on major roadways, LPS allows me to "filter out" some of
the visual distraction and concentrate on the task at hand.

Quoting from K.D. Alexopoulos, General Physics, Optics, First Edition,
Athens
1966, page 133: (translation from Greek mine)
<SNIP>
first because the emitted light penetrates fog without being
scattered significantly,

I.N. Galidakis

I've heard about LPS and improved visibility in fog for a long time; but
confirming data are elusive (although opinions are not ). Fog, being
white, scatters all colors equally; so why should yellow light somehow
scatter less? As a reference, I go back to a book entitled, Vision and
Highway Safety by M.J. Allen. (He was a professor of optometry at Indiana
University). He claims from his studies that using yellow automotive fog
lights, or indeed any color of light makes no difference in fog.

I wonder if the eye is being fooled by the improved visual acuity under LPS
lighting to be misled into thinking that vision is also improved.

Terry McGowan

I am aware that fog scatters the visible wavelengths fairly equally. As
one datapoint: fog that allows one to see the sun, even while reducing
its brightness by quite a few orders of magnitude, only reduces the sun's
cct by hundreds of kelvin.

Now one thing I suspect as a possible explanation for any actual
tendency of yellow light appearing to illuminate objects through fog and
for more-bluish light to appear to illuminate the fog: Scotopic/photopic
ratio.
It appears to me that in mesopic vision situations, scotopic vision
tends to contribute to a "sensation of illumination", while photopic
vision is what actually sees color and sharp detail. So light with higher
s/p ratio could cause more sensation of the fog being illuminated.

This might explain, if this is true, my grandfather's comment about
36-40 years ago that high pressure mercury lamps are supposed to be good
for the light to get through fog. These have lower s/p ratio than
most other lamps of similar CCT, and for that matter lower s/p ratio
than even the higher CCT subset of incandescents.

I google for s/p ratios, and find 1.41 for 2850 K incandescent and .8
for clear high pressure mercury vapor. Phosphored MV should have s/p
ratio slightly less than clear MV.

- Don Klipstein ([email protected])

 

[Paul M. Eldridge]

Years ago, some colleagues and I compared the visibility characteristics of
LPS, HPS and phosphor-coated mercury in a roadway lighting situation. We
matched luminances on various gray and neutral-colored objects and then
measured the visibility of those objects with a visibility meter. There was
little difference among the lamps as far as the overall visibility of the
objects was concerned; but we did notice that, under LPS lighting, visual
acuity (ability to see details) was somewhat better. That makes sense, of
course, since LPS is almost monochromatic and so produces less chromatic
aberration in the eye than the other sources. We didn't note any depth
perception effects.

Terry McGowan

Thanks, Terry; I know very little about roadway lighting, so I
appreciate your comments. I guess the trend is towards high mast
HID/SON, which makes sense on many levels and if that's the case, the
days of LPS will soon draw to a close.

Now if someone could develop an intelligent version that automatically
adjusts light output based on traffic volume and/or time of night or,
better yet, changing road conditions (e.g., dry pavement versus snow
covered), comfort and safety could be further enhanced, plus the
energy savings would be substantial.

Cheers,
Paul

 

[Paul M. Eldridge]

Paul,

The Street Lighting Control you ask for already exist.

See a collection of Street Lighting Controls links on my del.icio.us
web site.
http://del.icio.us/JohnSRichards/streetlightingcontrols

There are about 75 URLs connected to this tag.
Please advise if there are others I should add.

Some of the most interesting are:
http://www.dellux.ca/
http://www.streetlightiq.com/
http://www.holophane.com/roam/default.asp
http://www.metrolight.com/

Hope this helps.

John S. Richards

Hi John,

Thanks for providing us with the link to your reference page, as well
as these various manufacturers -- there appear to be some great
products out there that I hope will do well in the marketplace.

Best regards,
Paul

 

[Paul M. Eldridge]

Did you ever have any of the SLI/H linear sodium lamps over there? In
case anybody doesn't know what I'm talking about, they are these
things:

http://www.lamptech.co.uk/SLI.htm

The ones which I have are the same as the Atlas 140W one, but mine are
branded Thorn. They must have been fairly unusual even hear, as I'd
never seen one until a few years ago. The outer envelope and caps of
the 140W and 200W lamps are the same size as a three foot T12
fluorescent tube.

I'm afraid I can't provide you with a good answer on this; they may
have been used here in North America, but I'm not familiar with them.
Perhaps Victor or Terry can confirm this for us.

Cheers,
Paul

 

[Don Klipstein]

In <b878b3b9-b8bc-4d69-8ae2-ee253da78aa3@e25g2000prg.googlegroups.com>,

What's s/p ratio?

It is scotopic/photopic ratio. Photopic output is lumens, which is 683
times watts in each wavelength times photopic function of that wavelength.
Photopic function is "V lambda", except a slightly updated version was
adopted in 1988.
Scotopic output is "scotopic lumens", which is 1700 times watts in each
wavelength times scotopic function of that wavelength. The scotopic
function is "V-prime lambda".

I don't think there are any clear HP mercury lamps available here, at
least not ones for general purpose lighting use; there are specialised
ones.

I figure "deluxe white" mercury will have s/p ratio maybe 7-8% less than
clear mercury. The phosphor increases photopic output by roughly 7-9%
(initially). I am assuming no change in "scotopic lumen" output because
the red phosphor output has very little of this, unlikely more than the
scotopic lumens in other wavelengths lost by the phosphor since the
phosphor has some absorption and reflects some light to lamp parts that
absorb light.

- Don Klipstein ([email protected])

 

[Andrew Gabriel]

The OSRAM catalog lists their kind as NAT 200W-3.

It has a footnote on them saying "This type is not produced anymore, except as a
replacement until 1985".

I guess the above means OSRAM doesn't manufacture them anymore.

They'd gone from the UK by around the end of the 1970s.
I don't think any luminares taking them were produced
after the 1950's in the UK -- the luminares from that
point on were all SOX.

 

[TKM]

I'm afraid I can't provide you with a good answer on this; they may
have been used here in North America, but I'm not familiar with them.
Perhaps Victor or Terry can confirm this for us.

Cheers,
Paul

The story of low pressure sodium lighting is the U.S. is interesting --
especially to lighting geeks I know parts of it because LPS and HPS
were both marketed for outdoor lighting in the 1980s and I was usually the
one to present the HPS side the of argument to city councils, street
lighting engineers and electric utilities. But, the double-ended LPS lamps
were not marketed in the U.S. -- at least during my time in the lamp
business from 1961 - 1999. Philips introduced the "modern" LPS lamps to
North America in Canada during the late 70s - early 80s and promoted several
important installations including the Laurentian Autoroute which goes 55
miles from Montreal north into the ski country. Much of it was continuously
lighted and it gave the N.A. roadway lighting industry a taste of the
European roadway lighting approach used in the Netherlands, Belgium, France
and, of course, in the U.K.

In 1982 Philips purchased Westinghouse Lighting which gave Philips its first
major entrance into the U.S. lighting market. LPS lamps were unique and
Philips had lots of experience with them so they were promoted as new,
exclusive, energy-saving products. LPS roadway lighting systems then
appeared in Long Beach, CA and several smaller cities around the country.

Astronomers liked the monochromatic light output of LPS and organized
efforts to have them used for outdoor lighting around important
observatories. There were major installations in Tucson, AZ (Kitt Peak
Observatory); San Diego, CA (Mt. Palomar Observatory) and San Jose, CA (Lick
Observatory) as a result. LPS sockets grew to the point that a company in
Chicago began importing British LPS lamps from GEC; but these were the
single-ended designs so they could be used as replacements for the Phiips
products. Strategically, it was a good move for the LPS market since two
suppliers offered the promise of competition (important to government
buyers).

But HPS lamps had appeared in 1965 and the outdoor lighting industry was
already busy replacing HP Mercury with HPS when LPS lamps arrived in the
U.S. LPS promoters had a tough time for several reasons --- color being
one; but the main reasons were economic. HPS fixtures could be retrofitted
into systems using HP Mercury lamps (the main source used in ourdoor
lighting at the time) very easily sometimes without even changing the
luminaire. An LPS changeout required new fixtures and the light
distribution from the luminaires was such that lighting uniformity suffered.
LPS roadway lighting required either more poles/mile or taller poles for
uniform lighting and that drove costs higher.

Then, the clincher came -- improved HPS lamp life. Once HPS lamps were
rated for 24,000+ hours, electric utilities lost interest since those who
provide street lighting service want the longest lamp life possible. LPS
lamp life at the time was rated at 18,000 hours (Philips) and 20,000 hours
(GEC).

Terry McGowan

 

[Paul M. Eldridge]

The story of low pressure sodium lighting is the U.S. is interesting --
especially to lighting geeks ...

Terry McGowan

Thanks, Terry; it's great to learn more about the marketing of this
technology here in North America. I first recall seeing LPS used at
major road crossings and interchanges in our province back in the late
'60s -- most of these fixtures have since been replaced by HPS.
Everything else at that time would have been your standard issue merc
and to a much lesser extent fluorescent (e.g., the town of Truro was
once almost exclusively fluorescent and still has a large population
in active service today).

You know, it wasn't very long ago that the City of Toronto replaced
its incandescent street lighting with metal halide (mid '90's?). It's
been thirty years since I last visited Rome, but can anyone tell me if
that city still uses incandescent sources?

Cheers,
Paul