Sodium street lights being phased out...What does this mean?

[the lemming]

Like many places up and down the country, my town is replacing its sodium streetlights with LED lights. Any ideas how this will affect or change the light pollution at night?

More importantly will the changes improve night time viewing in towns such as mine?

[The Sailor]

I have a mix directly in front of my observatory, the sodium has been shielded for me but the LED is a different creature altogether. I do have LP filters but just for sodium, not sure how the LED are interfering with the seeing at the present time, have not had enough time with the weather, it's a wait and see for me I'm afraid.

Meant to say that here the street lights go out at midnight and I can see a difference in the sky when this happens.

Jim

[gkec]

Like many places up and down the country, my town is replacing its sodium streetlights with LED lights. Any ideas how this will affect or change the light pollution at night?

More importantly will the changes improve night time viewing in towns such as mine?

Looking at the spectra I reckon worse as the spectrum is spread out more. But I could be wrong. You will need new pollution filters.

[gkec]

Sodium spectrum for comparison.

[Anweniel]

I noticed some of the more recent LED street lamps are down lit (at least in my locality), I think councils are feeling some of the pressure from LP campaigns which would hopefully be a good thing as the sodium lamps near me have no shielding whatsoever and so emit as much light to the rear, sides and upwards cumulatively as they do downwards. The sodium lamp at the end of my back garden severely limits my astronomy. Hopefully any positives would outweigh the negatives but as always its a bit of a waiting game :/

[Merlin66]

IMHO there are no benefits to amateur astronomy from the newer white light LED lamps.

I'm translating a paper at the moment which discusses the issue.

The broadband emission of the LED cannot effectively be "filtered" out and will therefore cause more background in all imaging.....

[gkec]

IMHO there are no benefits to amateur astronomy from the newer white light LED lamps.

I'm translating a paper at the moment which discusses the issue.

The broadband emission of the LED cannot effectively be "filtered" out and will therefore cause more background in all imaging.....

I thought that might be the conclusion.

[RikM]

I think if you live in the country close to a town that changes from sodium to LED you will be better off because of the better shielding. If you actually live in the town, it will probably be worse because the LED lights are brighter and can't be filtered out. You will likely be worse off for imaging than visual.

[The Sailor]

Just took a photo from the observatory security camera of the lights at the end of my garden, the righthand light is shielded sodium and the left is LED:

Jim

[Lee M]

We've had a couple replaced near us recently. I would have thought it would be an improvement as they seem so much better directed*. One's on a slight bend and I don't see the lamp as I drive towards it, just the pool of light on the road. If it was still a standard sodium lamp I'd see the lamp head long before any illuminated patch of road.

However there will be some reflection upwards and it certainly looks like it might not be so easily dealt with.

One of those unintended consequeces situations I guess.

* From Jim's photo it looks like not all designs or installations may be as good.

[Pig]

The light output from LED's does not spread like that of a standard sodium lamp , The LED's light output has to be directed in order to be effective,

This will mean that they will need more LED's per streetlamp and the beam will have to be directed toward the target area, So if sheilded and directed properly from the onset they will be much better then the current sodium/other lamps.

The danger is if the light is not directed Im not sure what the effect will have on light pollution - They are very very bright and very very cheap to run thus they will have the potential to pop up everywhere (the return on investment cost savings are massive so they may get over sold ) .

Lets just hope our local councils do not get suckered by the producers and only buy the amount needed.

[Pig]

Looking at the spectra I reckon worse as the spectrum is spread out more. But I could be wrong. You will need new pollution filters.

You may have the solution here !!! RGB LED's combined together produces white light

[floppygoose]

The light output from LED's does not spread like that of a standard sodium lamp , The LED's light output has to be directed in order to be effective,

This will mean that they will need more LED's per streetlamp and the beam will have to be directed toward the target area, So if sheilded and directed properly from the onset they will be much better then the current sodium/other lamps.

The danger is if the light is not directed Im not sure what the effect will have on light pollution - They are very very bright and very very cheap to run thus they will have the potential to pop up everywhere (the return on investment cost savings are massive so they may get over sold ) .

Lets just hope our local councils do not get suckered by the producers and only buy the amount needed.

I agree with this, although I think our only saving grace is that the changes being made to street lighting by local authorities is to save money, so will probably want to buy as few as they can get away with.

Phil

[Monty]

They also dim as they get old, at least this has happended to the ones where I used to live. After twelve months you do notice a difference and they can of course be dimmed.

I wonder how long before someone has a driving accident when entering a brightly lit junction from a dark road?

[Caelus]

Some of these new LED street lights have appeared in villages near me, particularly in Woodhall Spa. About a quarter or half mile stretch near the golf course has had them installed and the difference both in colour and light pollution with the old sodium monstrosities is quite remarkable. I can only judge from the perspective of someone drives through the village, but the light they produce is a "proper" white and shines in clearly defined pools of light in which you can discern actual colours rather than shades of orange.

Most notably there seems to be almost no "spill" of light from them and outside the area of illumation it is quite dark. The stretch of road is lined with mature trees with overhanging branches and there is literally no upwards illumination under the new lights but very apparent omnidirectional illumation from the old sodium ones.

[DaveS]

I really don't see why they couldn't fit yellow LEDs, as these would be more efficiant, and directional. They could also be filtered with current LP filters.

[DaveS]

Sodium spectrum for comparison.

That's from a HP sodium lamp, showing classic self-absorbtion from the resonance lines. To me the ideal would be a LP sodium with a relativly broad-band filter letting only the D lines through, then LP could be eliminated with a simple notch filter.

It's lees about the lanp and more about the fitting it's in. Even a Sodium lamp can be made directional in a well designed fitting. Trouble is, a well designed, directional fitting might cost a few pennies more than the cheap bits of tim the councils insist on fittin up.

[The Sailor]

Trouble is, a well designed, directional fitting might cost a few pennies more than the cheap bits of tim the councils insist on fittin up.

The cheap bit of trim which actually looks like lawn edging the council put up on the offending light at the bottom of my garden has been in place almost a year now and has withstood whatever the weather has thrown at it, kudos to the council for doing a great job and keeping the costs down

Jim

[badgerchap]

We've had them installed on the road that passes in front of my viewing area, and I must say I have noticed quite a marked decrease in LP as they ar downlighters. Doesn't stop the glare of passing cars though! GRRRR!

[DaveS]

How we need really BLACK roads to stop the light coming down being reflected straight back up again.