UK replacing sodium street lights with LEDs, "to save electricity"?

[Artlav]

I've been looking at some news from UK lately, where they apparently try to save money on street lighting.
http://www.bristolpost.co.uk/Burglars-afraid-dark-Crime-falls-Bristol-street/story-13952633-detail/story.html

Some places turn off lights for the most of the night, which despite the fears of increase in crime rate seem to turn out ok.
But what caught my attention are the other places.

To quote:

A similar programme has begun in North Somerset, while in Bristol the council is taking a different tack by replacing light bulbs with state-of- the-art LED ones which are brighter and use less electricity.

We do feel there are savings to be made from converting all of our street lighting to more energy-efficient white light. This is why we are currently replacing around 34,000 sodium lights with new white lights.

There is also peculiar explanation on Bristol's official site:
http://www.bristol.gov.uk/page/white-light-replacement-programme

White light provides better colour rendering than standard yellow/orange type streetlights so the eye is able to see objects more easily. This means the actual amount of energy required to provide a suitable level of visibility can be reduced by around 40%.

How is that supposed to work?
I was under impression that the sodium lights were the most energy efficient lights there are, with LEDs quite a bit behind.
And the efficiency in question  is measured in lumens per watt, which are defined in terms of human eye sensitivity, making the last argument peculiar.

Am i missing something?

[cjo20]

I think the argument is that because white light lets you see if more than just slightly different shades of orange, there needs to be less white light hitting a surface than sodium-lamp light for the brain to extract the same amount of information from the scene, so they can be run at a lower power

[electronics man]

These new led lights are far too bright there have been many complaints that people are being kept awake at night due to the street lights shining into there bedrooms.

[IanB]

Also, astronomers will hate them. The orange sodium light is monochromatic so there is some ability to filter it out. White light is broad spectrum, so the opportunities to filter it are greatly reduced.

[ajb]

The human eye has a sort of bell shaped response curve to the visible spectrum, with a peak somewhere between 510 and 560nm, depending on the adaptation of the eye to ambient conditions (photopic, scotopic, or mesopic vision, depending on if the eye is adapted to bright, dark, or intermediate conditions).  In darker conditions, the eye responds most strongly to wavelengths in the 510-530nm area.  Sodium lamps have most of their output in the longer wavelengths, with a sharp peak around 590nm and a big lump in the ~600-620nm range.  Since the eye's response drops off fairly sharply to either side of the peak, these wavelengths appear to be relatively dim, watt for watt*, relative to wavelengths near the peak response point. 

With LEDs, you can better tailor the phosphors to have more of your output concentrated in the wavelengths to which the eye is more sensitive, and thus for the same or less wattage, you get a brighter light.

Furthermore, with white light you get better color rendering, which means better contrast, which means watt-for-watt* you get better visual acuity.

*radiometric watts, meaning actual watts of light emitted; obviously for total energy efficiency you have to account for the conversion efficiency of the light source.

[rollatorwieltje]

LEDs may also have a better lamp life time. I intentionally wrote "may", as it's all depends on the driver and LED arrangement. Most LED lights I've seen are garbage. Some sort of "constant current" driver dumping into several parallel strings of LEDs. Maybe that works when you match the LEDs, but most of the time it will fail about as fast as a typical halogen bulb.
At least you can advertise your building as being energy efficient, as it's fitted with "the latest high efficiency LED technology".

[rdl]

If they ever install one of those awful, way too bright, glaring, overly blue LED streetlights in front of where I live, I will shoot it out at least once. Or at least complain loudly.

[SL4P]

I'd be questioning the usefulness of white LEDs in 'foggy' old England.

They'll see NOTHING with bright white lighting, whereas they'll see a lot more with the contrasting effect of the pure spectrum of the yellow sodium lamps.

But this may just be another example of younger engineers not understanding why the 'older' engineers did a specific thing.

[NiHaoMike]

The efficiency can be improved many fold if they add some motion sensors. LEDs are very well suited for dimming, while sodium lamps are not.

[Bored@Work]

Oh come on, all you lot want is to have your good old gas lighting back. Complete with the lamplighter guy walking around, igniting them at sunset and turning them off at sunrise, and checking the whole night if they still burn.

Or even better fatwood. Worked since prehistoric times, why replace it with some modern fad?

I mean serious, why do you lot touch modern stuff like electronics at all? It is all the work of the devil, you know. Back to your caves, guys. Back to your caves.

[peter.mitchell]

Oh come on, all you lot want is to have your good old gas lighting back. Complete with the lamplighter guy walking around, igniting them at sunset and turning them off at sunrise, and checking the whole night if they still burn.

Or even better fatwood. Worked since prehistoric times, why replace it with some modern fad?

I mean serious, why do you lot touch modern stuff like electronics at all? It is all the work of the devil, you know. Back to your caves, guys. Back to your caves.

Yeah, jeez, may as well walk around with a burning stick just to make em happy.

[vk6zgo]

I'd be questioning the usefulness of white LEDs in 'foggy' old England.

They'll see NOTHING with bright white lighting, whereas they'll see a lot more with the contrasting effect of the pure spectrum of the yellow sodium lamps.

But this may just be another example of younger engineers not understanding why the 'older' engineers did a specific thing.

Also LED's weren't available when sodium vapor lamps were originally selected.

What contrast?--All those colours with a bit of yellow appear as yellow,white appears as yellow,shades of grey are yellow.

Sodium lights were selected because they cost less to run than colour corrected mercury vapour lights,which when they are in good condition,offer the best type of lighting.

Sodiums,on the other hand, are about the worst possible form of street lighting.
Unless an object has some orange/yellow component in its colour,it is effectively invisible.

Young Engineers?---Most older Australians spent the first half of their lifetime with either incandescent or Colour-corrected Mercury vapour street lighting--the mass replacement of these with sodium lamps mainly occurred in the 1980s.

The Brits used them many years before that--when I was in the UK in 1971,I nearly got run over by an "invisible"taxi at a crosswalk.
The Taxi was dark blue,with only its parking lights on,so that's why I didn't see him,but he didn't see me either.
(For many years,you could drive on "parkers" in the UK in built up areas---the law had just changed,but it took a while for people to catch on).

It was also great fun,walking all over Southampton,looking for a pink Cortina hire car.
It was where I thought it was,but it looked like a Yellow Cortina.

[IanB]

Young Engineers?---Most older Australians spent the first half of their lifetime with either incandescent or Colour-corrected Mercury vapour street lighting--the mass replacement of these with sodium lamps mainly occurred in the 1980s.

The Brits used them many years before that--when I was in the UK in 1971...

Yes, they were phased in around that time I guess. The street where I grew up in the 60's was lit by fixtures with 100 W incandescent bulbs in them. I found this out by asking for some of the old bulbs when a maintenance crew was going round replacing time expired bulbs for fresh ones.

I also remember places with (non-colour corrected) mercury vapour street lighting around the same time. It was a weird contrast seeing "green" street lights compared to the more familiar yellow ones. I didn't like the mercury lamps though. They seemed very cold and unwelcoming.

[Zero999]

These new led lights are far too bright there have been many complaints that people are being kept awake at night due to the street lights shining into there bedrooms.

It's not just the brightness which wakes you up but the shorter wavelengths which disrupt sleep more than the longer wavelengths.

This is a valid complaint. I think warm white should be used in residential areas, as this would be less of a problem.

The efficiency can be improved many fold if they add some motion sensors. LEDs are very well suited for dimming, while sodium lamps are not.

Yes, I've wondered why they don't do that. On main roads, the sensors could also turn on the lamps several hundred meters ahead, when a car passes.

[Codemonkey]

They'll see NOTHING with bright white lighting, whereas they'll see a lot more with the contrasting effect of the pure spectrum of the yellow sodium lamps.

Complete rubbish. I live not far away from a road that's just had sodium lamps replaced with nice modern LED lights. The road is considerably better lit now. Driving down the road as they were replacing the lamps (2/3 LED, then the remaining 1/3 section still sodium lit), it was obvious that the LED lit section was much better on the eyes than the sodium, probably due to the broader spectrum of light making it easier to distinguish things, and also the light pollution was much reduced due to the design of the luminaire itself.

[G7PSK]

Don't forget that this decision to fit LED's instead of sodium lamps has been made by a City council, therefore the saving could be very small or non existent. They talk about CO2 savings and other green agenda but they will have used half a forest of trees in coming to this conclusion and the cost of making the switch not the lamp cost just the contractor cost will in all likelihood be more than several years cost of running the sodium lamps.
Now if they went around lighting all the pot hole in the roads or better still filling them in. But they always seem able to find the money for some grand scheme but never have any money for maintenance.   

[SeanB]

Sodium lamps and mercury lamps can have a multi decade lifetime if well designed and made. This was solved in the 1950's for mercury lamps, where they made lamps that would last for 15 years in street lighting use, and which could run for more than 30 years, albeit with decreased light output, in many cases. Simple control gear as well, which would also last the 30 years with no degradation even after multiple storms and many close strikes with lightning.

Of course then the manufacturers "optimised" the design so that they only lasted 10 years, then 5 years. Same with the ballasts, "optimised" for smaller cores that ran a lot hotter and thus would burn out in about 20 years. All done to reduce manufacturing cost and maximise profit.

The mercury lamps as well are very easy to recycle, you just need the metro to have a drum that the lamps are crushed into  which is then sent when full to have the glass, mercury, brass, tungsten, lead and nickel recovered and remade into new lamps. All simple processes and all easy to do. Sodium lamps are slightly more difficult as they are made with 2 or more glass types and with quartz tube as well, but they can still be recycled as well. Compare to LED lamps with every element in the periodic table in there in small amounts and difficult to separate out from the product easily, with most being a lot more toxic than mercury and lead.

[Marco]

These new led lights are far too bright there have been many complaints that people are being kept awake at night due to the street lights shining into there bedrooms.

Can't they just turn them down and save even more energy?

[Richard Crowley]

I guess the weather there is so lousy, there are no astronomical observatories in the region to complain about the light pollution.
http://en.wikipedia.org/wiki/Sodium-vapor_lamp#Light_pollution_considerations

[con-f-use]

I would expect LEDs are easier on infrastructure requirements, maintenance and availability/production costs.
 

I don't really get why people are that obsessed with making lighting more efficient. The share in total electricity consumption is small (about 13% in your average first world country). Industrial machinery etc. and a ton of other stuff is a more rewarding target for optimization. The effort is better spend elsewhere first.

Also, astronomers will hate them. The orange sodium light is monochromatic so there is some ability to filter it out. White light is broad spectrum, so the opportunities to filter it are greatly reduced.

But it would be much less intense and absorption works better. On top of that scientific telescopes are build where there is no light smog anyway and Britain is not interesting to astronomers (bad weather, bad geographic location, bad altitude). Even as an astro physicist, I wouldn't say we are near that important for the argument even to be brought up jokingly.

[steve30]

Some of our main roads have had new LED lights installed. The better colour rendering definitely makes it easier to see things.

Now, as far as sodium goes, does anyone still make Low Pressure Sodium lamps any more? They don't seem to be widely available. Many of our low pressure sodium fixtures are very old, and in some cases, they have come and replaced entire sets of lamp posts. Our street had a mixture of old low pressure sodium, old high pressure sodium and new high pressure sodium lamps, so they recently came and modernised it by fitting all new high pressure sodiums. I think there probably is a good case for 'modernisation'.

What worries me is fluorescent lights. Over the last few years, our council has replaced many residential street lights with fluorescent ones. I'd imagine they aren't any better than sodium.

[con-f-use]

Another big problem is the wildlife being irritated by street lights. Especially insects. At first it might sound good and you see the occasional bat or bird finding easy hunting grounds around street lights. But actually a lot of insects die and don't reproduce leading to less food. Other animals get disrupted in their usual daily pattern and can't adapt. A biologist told me LEDs are better way better for insects.

[G7PSK]

I guess the weather there is so lousy, there are no astronomical observatories in the region to complain about the light pollution.
http://en.wikipedia.org/wiki/Sodium-vapor_lamp#Light_pollution_considerations

There are a few radio observatory's in the UK as well as optical ones, there could be a concern with led street lighting causing Rf pollution, The RSGB has recent raised concerns about led lights and Rf pollution and is conducting a study. There are also concerns about Rf pollution from solar cells as well or the inverters and control gear associated with them.

[Mr Smiley]

They'll see NOTHING with bright white lighting, whereas they'll see a lot more with the contrasting effect of the pure spectrum of the yellow sodium lamps.

Complete rubbish. I live not far away from a road that's just had sodium lamps replaced with nice modern LED lights. The road is considerably better lit now. Driving down the road as they were replacing the lamps (2/3 LED, then the remaining 1/3 section still sodium lit), it was obvious that the LED lit section was much better on the eyes than the sodium, probably due to the broader spectrum of light making it easier to distinguish things, and also the light pollution was much reduced due to the design of the luminaire itself.

SL4P was referring to the good old UK foggy days, where mist and fog from surrounding areas badly effected visibility day or night.

Clearly stating that the pure spectrum of sodium lights would provide a longer reaching illumination of the surrounding area than a led light source. 

 

[BennyBoy]

They have them installed where I am(Oakland, Cal) They are not all that bright, there's a bright sort of spot on the road(say 10 meters DIA), but overall there's less light. It also shows in my security cameras to have less light.