San Jose LED Streetlamps

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

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.

In , Martin Brown wrote in part:

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 ( snipped-for-privacy@misty.com)

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? ;-)

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

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

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.

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

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

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

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)

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.

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.

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

?? "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...

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

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).

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.

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

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 :-).

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.

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.

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

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

Is there still a LPS lamp production line anywhere in the world? Its been so long since I've seen active LPS in the North Eastern US..

Steve

It's not quite that bad. The above LEDs (IIRC) (cree XPG) quote 80% lumen maintainance at 70000 hours at 70C.

For any reasonable sized streetlamp, operating at night in ambients of under 30C, this is not hugely challenging - though it does require some thoguht.

US always was a mercury vapour country. UK and Belgium still have about

50% installed base of LPS with HPS making inroads into city centres. They date from the 60's when the yellow light fog penetration was a benefit and a second wave of them installed in the mid 70's for energy efficiency during the oil shocks and 3 day week power cuts era.

Someone must still be making them. Still a stock item at RS although their price is not the best.

Mercury street lighting is rare here although is used in my village.

Regards, Martin Brown

It depends. They are currently just fine for spotlamp replacements. A 50W halogen will put out ~700lm. You can do this with either:

5 LEDs at ~1.1W, for a total power input of around 6.2W (with a 90% efficient ballast), or two LEDs at ~11W input. Guess which is going to come to market first.

Only 'normal' 5mm LEDs have defined patterns. The above LEDs I mentioned come in a 3.5mm*3.5mm square package, with the light emitted into most of a hemisphere from a source about 2*2mm. The optics totally defines the problem.

Presumably. However, comparing apples and oranges may not always be unfair. If you have no buisness case for upgrading your existing low efficiency ballasts, and there is no grant money for efficient ballasts, but there is grant money for LEDs, then comparing the existing ballasts with the LEDs is not completely unfair. (assuming the large ballast losses quoted are representative of the existing stock)

[snip]

Will/Do those devices include power-factor correction? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
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