San Jose LED Streetlamps

Martin Brown
Guest

Thu Mar 11, 2010 5:20 pm

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

http://www.etcc-ca.com/component/content/article/48/2894-led-street-lighting-and-network-controls-san-jose

The legal disclaimer on page 1 rings alarm bells for me.

They go on to compare this bogus highly inefficient baseline SOX setup
with the luminous efficiency of the bare LED units without DC control
gear in the first table I. And so claim spuriously large energy savings
from making the conversion. The estimates further into the document are
slightly more realistic and by table XVII they do include control gear
for the LED systems (with some optimistic assumptions).

Nowhere do the numbers approach the 80% in the news article though.

Their numbers in W are
SOX 92.5 (extremely high for a 55W SOX tube)
LED 100% 75
LED 75% 52.4
LED 50% 34.9

My estimate is
SOX* 65 (Philips electromagnetic ballast)

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better choice
with a saving of 30% power for a $20 new ballast component retrofit.

Is there some obvious reason why modern SOX ballasts do not work well on
US mains or is this an attempt to make the old lamps look like they are
very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure sodium
lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least since
LED based luminaires should last 3-4x longer than SOX tubes.

Regards,
Martin Brown

Tim Wescott
Guest

Thu Mar 11, 2010 5:32 pm

Martin Brown wrote:

Quote:

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

http://www.etcc-ca.com/component/content/article/48/2894-led-street-lighting-and-network-controls-san-jose

The legal disclaimer on page 1 rings alarm bells for me.

They go on to compare this bogus highly inefficient baseline SOX setup
with the luminous efficiency of the bare LED units without DC control
gear in the first table I. And so claim spuriously large energy savings
from making the conversion. The estimates further into the document are
slightly more realistic and by table XVII they do include control gear
for the LED systems (with some optimistic assumptions).

Nowhere do the numbers approach the 80% in the news article though.

Their numbers in W are
SOX 92.5 (extremely high for a 55W SOX tube)
LED 100% 75
LED 75% 52.4
LED 50% 34.9

My estimate is
SOX* 65 (Philips electromagnetic ballast)

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better choice
with a saving of 30% power for a $20 new ballast component retrofit.

Is there some obvious reason why modern SOX ballasts do not work well on
US mains or is this an attempt to make the old lamps look like they are
very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure sodium
lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least since
LED based luminaires should last 3-4x longer than SOX tubes.

How much government money will PE&G get for changing to white LEDs?

How much government money will PE&G get for swapping out ballasts?

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Ian Stirling
Guest

Thu Mar 11, 2010 9:10 pm

Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote:

Quote:

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
snip
Best power LEDs are close to 100 lumens/watt now.

Not addressing all of this.

Best power LEDs are more like 140lm/W.
This is however not at their max output.
For example the Cree XP-G range can do 140lm/W at 1W, though about
80lm/W at 5W.

One potential for truly massive energy savings is actually real - if
implemented.
Lights with patterns defined at installation time.
Imagine an array of LEDs, each with a 8 degree optic, pointed so as
they overlap slightly. These are configured at install time to only
light the required elements.

95% efficient ballasts are available.

Don Klipstein
Guest

Fri Mar 12, 2010 2:04 am

In <aL8mn.38370$_v6.26671_at_newsfe08.iad>, Martin Brown wrote in part:

Quote:

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

<SNIP from here to edit for space>

I do agree that the advantage of the LEDs is overstated as is often the
case. However, the low pressure sodium is not quite 160 lumens/watt, but
145 in new condition. As the lamp ages, light output is largely constant,
and its power consumption increases slightly.

One significant disadvantage of sodium lighting is low scotopic/photopic
ratio. At streetlighting illumination levels of a few to several lux,
human vision is usually mesopic, which means both photopic and scotopic
vision are significantly functioning.

Low pressure sodium has an s/p ratio of .23, high pressure sodium has
s/p ratio usually around .62-.65, and higher luminous efficacy white LEDs
have s/p ratio usually 1.7-2.1. At streetlighting illumination levels,
light sources with higher s/p ratio can effectively provide a given degree
of illumination with less illumination according to the usual photometric
units such as lumens, candela and lux.

However, I seriously agree with doubting the figure for 80% energy
consumption reduction, even with higher s/p ratio light and improved
ability to direct where the light goes.

However, in the area where light pollution would affect the observatory
(mentioned somewhere in what I snipped out), I would keep the low pressure
sodium.

- Don Klipstein (don_at_misty.com)

Tim Williams
Guest

Fri Mar 12, 2010 3:38 am

"Don Klipstein" <don_at_manx.misty.com> wrote in message
news:slrnhpj17o.d36.don_at_manx.misty.com...

Quote:

One significant disadvantage of sodium lighting is low scotopic/photopic
ratio. At streetlighting illumination levels of a few to several lux,
human vision is usually mesopic, which means both photopic and scotopic
vision are significantly functioning.

Low pressure sodium has an s/p ratio of .23, high pressure sodium has
s/p ratio usually around .62-.65, and higher luminous efficacy white LEDs
have s/p ratio usually 1.7-2.1. At streetlighting illumination levels,
light sources with higher s/p ratio can effectively provide a given degree
of illumination with less illumination according to the usual photometric
units such as lumens, candela and lux.

Obviously then, they should install loads of gallium phosphide. Green is
supposed to be the brightest percieved color.

Maybe they should start in Sweden.. they'd be more comfortable with the
"Borg" look, right? ;-)

Quote:

However, in the area where light pollution would affect the observatory
(mentioned somewhere in what I snipped out), I would keep the low pressure
sodium.

Hmm, monochromatic LEDs are still pretty easy to filter. GaP linewidth
might be 20nm, more than the laserlike sodium doublet, but not as bad as
phosphor anything (white LEDs, fluorescents, etc.).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Dirk Bruere at NeoPax
Guest

Fri Mar 12, 2010 6:05 am

On 11/03/2010 16:20, Martin Brown wrote:

Quote:

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

http://www.etcc-ca.com/component/content/article/48/2894-led-street-lighting-and-network-controls-san-jose

The legal disclaimer on page 1 rings alarm bells for me.

They go on to compare this bogus highly inefficient baseline SOX setup
with the luminous efficiency of the bare LED units without DC control
gear in the first table I. And so claim spuriously large energy savings
from making the conversion. The estimates further into the document are
slightly more realistic and by table XVII they do include control gear
for the LED systems (with some optimistic assumptions).

Nowhere do the numbers approach the 80% in the news article though.

Their numbers in W are
SOX 92.5 (extremely high for a 55W SOX tube)
LED 100% 75
LED 75% 52.4
LED 50% 34.9

My estimate is
SOX* 65 (Philips electromagnetic ballast)

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better choice
with a saving of 30% power for a $20 new ballast component retrofit.

Is there some obvious reason why modern SOX ballasts do not work well on
US mains or is this an attempt to make the old lamps look like they are
very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure sodium
lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least since
LED based luminaires should last 3-4x longer than SOX tubes.

Regards,
Martin Brown

Also factor in lifetime and cost of replacement.
How much does it cost to replace one streetlamp?
How often?
It's going to take at least 2 guys, a special truck and traffic
management for each instance. Also factor in the cost of disruption of
traffic.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show

Paul Keinanen
Guest

Fri Mar 12, 2010 9:02 am

On Thu, 11 Mar 2010 14:10:50 -0600, usenet_at_mauve.plus.com (Ian
Stirling) wrote:

Quote:

One potential for truly massive energy savings is actually real - if
implemented.
Lights with patterns defined at installation time.
Imagine an array of LEDs, each with a 8 degree optic, pointed so as
they overlap slightly. These are configured at install time to only
light the required elements.

Current street light fixtures are really bad, outputting light in
placed, in which it is not needed, some even output directly into the
sky causing light pollution. Others output a lot of light close to the
horizontal plain, falling directly into the eyes of pedestrians and
drivers. This will destroys the night adaption of the eye and higher
illumination levels on the ground is required.

Unfortunately, the current street infrastructure with light poles at
every 30 m is quite suboptimal. Either the distance between light
poles should be similar to the pole height or a horizontal bar should
be suspended above the street center line and the light fixtures can
then be installed every few meters on the bar. In such a situation,
LEDs would work quite effectively.

The life expectance for various LEDs used for illumination is strongly
dependent on the thermal conditions of the LED itself. To reach such
huge numbers quoted would require connecting it to a good heatsink
which is cooled by ice cold water Smile

. With a realistic heat sink in a
light fixture, the life expectance is much shorter.

Greegor
Guest

Fri Mar 12, 2010 9:14 am

On Mar 11, 11:05 pm, Dirk Bruere at NeoPax <dirk.bru...@gmail.com>
wrote:

Quote:

Also factor in lifetime and cost of replacement.
How much does it cost to replace one streetlamp?
How often?
It's going to take at least 2 guys, a special truck and traffic
management for each instance. Also factor in the cost of disruption of
traffic.
Dirk

I heard second hand that LED tail light assemblies
have become wildly popular with Over The Road
Semi truck operators because down time is so
painful and costly for them. I looked them over
at a local farm supply place and noticed that they
were like triple the cost of the exact same
tail light assembly with bayonet incandescent.

It's easy to envision the HUGE cost of changing
street lamps could eclipse energy costs, bulb
costs etc. ANY LED assembly that can hit a
huge MTBF would be able to realize a ROI
based on replacement cost alone, on top
of the energy savings.

But if they compromise on the lumens etc.
the cost of LAW SUITS could be a serious
issue as well.

Can't the LED street lights eliminate ballasts
and get the cost way down?

On the other hand a suburb here got
some fancy decorative street lights
about 6 years ago and the things
cost something like $10K per pole,
even in quantity!

I would submit that the cost of materials
and workmanship has little to do with it.

Martin Brown
Guest

Fri Mar 12, 2010 10:10 am

Tim Wescott wrote:

Quote:

Martin Brown wrote:

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better
choice with a saving of 30% power for a $20 new ballast component
retrofit.

Is there some obvious reason why modern SOX ballasts do not work well
on US mains or is this an attempt to make the old lamps look like they
are very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure
sodium lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least
since LED based luminaires should last 3-4x longer than SOX tubes.

How much government money will PE&G get for changing to white LEDs?

Roughly $50M/62k = $800 per unit.

Quote:

How much government money will PE&G get for swapping out ballasts?

Probably none.

You can call me naive if you like, but I had assumed that PE&G were just
selling the electricity that the street lights consume. And that they
were acting as consulting engineers to the city council.

I did wonder if they had already changed to electronic ballasts and were
stiffing the city for 90W for each 55W lamp according to the original
contract whilst supplying only 60W with the new ballasts. Seems pretty
odd that a city that cannot afford to run all its installed low pressure
sodium lights can afford to spend $50M on a boondoggle like this.

At least in a city with mercury lighting there would be a prospect of
making real energy savings with LED technology.

Regards,
Martin Brown

Martin Brown
Guest

Fri Mar 12, 2010 10:27 am

Ian Stirling wrote:

Quote:

Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote:
This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
snip
Best power LEDs are close to 100 lumens/watt now.

Not addressing all of this.

Best power LEDs are more like 140lm/W.
This is however not at their max output.

I have a torch that uses one and is highly collimated. I hadn't realised
they derate with power quite that fast and only looked at max output.
Best I had seen was 120lm/W under lab conditions and infinite heat sink.

Lumiled also seem to have announced some 140lm/W devices.

Incidentally does anyone know if the quantum efficiency of modern LEDs
still improves further when you dunk them in LN2 ?
(that is if the thermal shock doesn't kill them)

Quote:

For example the Cree XP-G range can do 140lm/W at 1W, though about
80lm/W at 5W.

When they can do 140lm/W at 5-10W they will be competitive as spotlamp
replacements (a position where CFLs are truly dreadful). Pricing is
still an issue even allowing for the longer lifetime.

Quote:

One potential for truly massive energy savings is actually real - if
implemented.
Lights with patterns defined at installation time.
Imagine an array of LEDs, each with a 8 degree optic, pointed so as
they overlap slightly. These are configured at install time to only
light the required elements.

The built in collimation makes them excellent for roadside signalling.
very bright at long range and not too dazzling when you get close to.

I don't doubt their day will come, but I reckon the early adopters like
San Jose are headed for a very nasty surprise.

Quote:

95% efficient ballasts are available.

And I presume that also holds for solid state HF SOX ballasts too.
Certainly low voltage ones exist at 95% efficiency, but the common mains
SOX ballasts like Philips BSX355 waste about 10W (and not 45W).

Regards,
Martin Brown

Robert Baer
Guest

Fri Mar 12, 2010 11:44 am

Martin Brown wrote:

Quote:

This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

http://www.etcc-ca.com/component/content/article/48/2894-led-street-lighting-and-network-controls-san-jose

The legal disclaimer on page 1 rings alarm bells for me.

They go on to compare this bogus highly inefficient baseline SOX setup
with the luminous efficiency of the bare LED units without DC control
gear in the first table I. And so claim spuriously large energy savings
from making the conversion. The estimates further into the document are
slightly more realistic and by table XVII they do include control gear
for the LED systems (with some optimistic assumptions).

Nowhere do the numbers approach the 80% in the news article though.

Their numbers in W are
SOX 92.5 (extremely high for a 55W SOX tube)
LED 100% 75
LED 75% 52.4
LED 50% 34.9

My estimate is
SOX* 65 (Philips electromagnetic ballast)

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better choice
with a saving of 30% power for a $20 new ballast component retrofit.

Is there some obvious reason why modern SOX ballasts do not work well on
US mains or is this an attempt to make the old lamps look like they are
very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure sodium
lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least since
LED based luminaires should last 3-4x longer than SOX tubes.

Regards,
Martin Brown
?? "Low pressure sodium (lamps) are almost monochromatic narrowband

emitters" ??
Hmmm..a number of nice yellow bands, a number of red bands, a number
of green bands, not to mention a few lonely ones here and there.
Yup...monochromatic...

Robert Baer
Guest

Fri Mar 12, 2010 11:45 am

Tim Wescott wrote:

Quote:

Martin Brown wrote:
This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost
200 l/W with optimised solid state ballast. They are mandated near
world class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and
could be easily half that.

http://www.etcc-ca.com/component/content/article/48/2894-led-street-lighting-and-network-controls-san-jose

The legal disclaimer on page 1 rings alarm bells for me.

They go on to compare this bogus highly inefficient baseline SOX setup
with the luminous efficiency of the bare LED units without DC control
gear in the first table I. And so claim spuriously large energy
savings from making the conversion. The estimates further into the
document are slightly more realistic and by table XVII they do include
control gear for the LED systems (with some optimistic assumptions).

Nowhere do the numbers approach the 80% in the news article though.

Their numbers in W are
SOX 92.5 (extremely high for a 55W SOX tube)
LED 100% 75
LED 75% 52.4
LED 50% 34.9

My estimate is
SOX* 65 (Philips electromagnetic ballast)

And so by the time you add in the overhead of 5-10% for control gear I
reckon the 100% LEDs will use almost as much energy as the original
installation is allegedly using at present. I reckon they are in for a
nasty surprise after they finish spending $50M on these new
streetlights. Retrofitting decent ballasts would be a far better
choice with a saving of 30% power for a $20 new ballast component
retrofit.

Is there some obvious reason why modern SOX ballasts do not work well
on US mains or is this an attempt to make the old lamps look like they
are very inefficient so as to create momentum for a change to LEDs?

I am aware that some residents of San Jose hate the low pressure
sodium lights on largely cosmetic grounds of poor colour rendering.

There is undoubtedly a maintenance saving since in theory at least
since LED based luminaires should last 3-4x longer than SOX tubes.

How much government money will PE&G get for changing to white LEDs?

How much government money will PE&G get for swapping out ballasts?

...and how much of that is TAXPAYER money???

Martin Brown
Guest

Fri Mar 12, 2010 12:20 pm

Robert Baer wrote:

Quote:

Martin Brown wrote:
This is continuing from a discussion from an astronomy forum where the
"massive" energy savings of 80% were claimed by San Jose for changing
from astronomer friendly low pressure sodium SOX lights to white LEDs.
Citing the following article in the Mr Roadshow column of the Mercury
News. But the numbers just do not add up. Anyone care to comment?

http://www.mercurynews.com/mr-roadshow/ci_14521828

I can't see any obvious reason why European experience of these lights
does not apply in the USA.

Low pressure sodium gives something like 160 lumens/watt and almost
200 l/W with optimised solid state ballast. They are mandated near
world class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

?? "Low pressure sodium (lamps) are almost monochromatic narrowband
emitters" ??

YES. Almost 95% of their visible light output is in the yellow D-lines.
The next strongest line in the visible is less than 0.5% of the total.

Someone has drawn the spectra of the elements and various light sources
with a linear scale spectral graph. You can just about see the third
brightest visible line if you know where to look (569nm).

http://ioannis.virtualcomposer2000.com/spectroscope/elements.html#sodium

There is a 10% line output in the near IR around 820nm but modern tubes
filter it with an InO window to improve thermal efficiency.

Quote:

Hmmm..a number of nice yellow bands, a number of red bands, a number
of green bands, not to mention a few lonely ones here and there.
Yup...monochromatic...

In power terms almost everything goes into the 2 sodium D-lines at 589nm
and 589.6nm. There are some faint spectral lines but they are negligible
(and unlike mercury they don't sit on any astrophysically important
wavelengths). Low pressure sodium light is pure enough to demonstrate
interference effects in lab experiments requiring monochromatic light.

By any reasonable definition it is monochromatic light.

Regards,
Martin Brown

Paul Keinanen
Guest

Fri Mar 12, 2010 12:27 pm

On Thu, 11 Mar 2010 14:10:50 -0600, usenet_at_mauve.plus.com (Ian
Stirling) wrote:

Quote:

Best power LEDs are more like 140lm/W.
This is however not at their max output.
For example the Cree XP-G range can do 140lm/W at 1W, though about
80lm/W at 5W.

At least Cree seems to specifies the characteristics at 25 C junction
temperature. In the real world, this is a valid assumption only during
a few seconds at turn on. The output drops by 20-30 % for higher
junction temperatures.

It seems to be very hard to get any reliable MTBF figures, but
assuming that the MTFB is halved for each 10 C increase in
temperature, which is typical for semiconductors, you really have to
operate the device well below the maximum junction temperature.

For long life, you will have to operate the device below 100 C
junction temperature. From the heatsink design point of view, this
resembles the problems when building audio power amplifiers using
germanium transistors a few decades ago Smile

.

In order to obtain the claimed efficiency and long life, you really
have to operate a "5 W" device at 1 W, thus in order to get the
expected illumination, you have to use 5 times the number of devices,
thus making it even less economically attractive.

When reading specifications for power LEDs, you must be very careful
to check the actual condition in which the claims are valid. While the
marketing claims for some ordinary semiconductor part might be a bit
excessive, the marketing claims are much worse in the power LED
industry.

By the way, San Jose and other similar places close to the equator are
nasty places for LED street lights due to the long warm nights, making
it hard to dissipate the heat into the environment. While at higher
latitudes, street lights might be needed for 18-24 hours during the
winter, transferring the heat into subzero ambient temperature is much
easier. During the summer, only a few hours (if any) is needed and
even then, the heat is easily dumped into a moderate temperature air.

Martin Brown
Guest

Fri Mar 12, 2010 1:07 pm

Don Klipstein wrote:

Quote:

In <aL8mn.38370$_v6.26671_at_newsfe08.iad>, Martin Brown wrote in part:

Low pressure sodium gives something like 160 lumens/watt and almost 200
l/W with optimised solid state ballast. They are mandated near world
class observatories (in this case Lick) because they are almost
monochromatic narrowband emitters and can be easily filtered out.

Best power LEDs are close to 100 lumens/watt now.

I looked up the PE&G report advocating this change and found that they
reckon to power a 55W SOX tube requires 92.5W so I guess they used a
half dead antidiluvian magnetic choke ballast as their baseline. I
reckon a typical modern ballast would be more like 10W at most and could
be easily half that.

SNIP from here to edit for space

I do agree that the advantage of the LEDs is overstated as is often the
case. However, the low pressure sodium is not quite 160 lumens/watt, but
145 in new condition. As the lamp ages, light output is largely constant,
and its power consumption increases slightly.

I think it also depends a bit on the lamp size and ballast. Some of the
newest HF ballasts are claiming 200lm/W but at reduced operating power
and as a result longer tube life.

Quote:

One significant disadvantage of sodium lighting is low scotopic/photopic
ratio. At streetlighting illumination levels of a few to several lux,
human vision is usually mesopic, which means both photopic and scotopic
vision are significantly functioning.

Low pressure sodium has an s/p ratio of .23, high pressure sodium has
s/p ratio usually around .62-.65, and higher luminous efficacy white LEDs
have s/p ratio usually 1.7-2.1. At streetlighting illumination levels,
light sources with higher s/p ratio can effectively provide a given degree
of illumination with less illumination according to the usual photometric
units such as lumens, candela and lux.

Agreed. I suspect they will be landed with a pig inn a poke.

Quote:

However, I seriously agree with doubting the figure for 80% energy
consumption reduction, even with higher s/p ratio light and improved
ability to direct where the light goes.

However, in the area where light pollution would affect the observatory
(mentioned somewhere in what I snipped out), I would keep the low pressure
sodium.

- Don Klipstein (don_at_misty.com)

Lick seem to be under the impression that they will be protected by
somewhat exotic amber LEDs with 6nm fwhm output late at night. I'd be
interested in finding sample of these super amber high power LEDs as the
best I can see are typically ~20nm fwhm centred on 590nm.

Ideal would be 585nm fwhm <10nm as a crude solid state demo sodium light
(and much less fragile to carry around).

Regards,
Martin Brown