LED street lights affecting plant growth?

Fire · February 2021

Has anyone encountered any hard evidence that (blue toned) LED street lights (or lights generally) would affect plant growth or animal behaviour? Our area has just changed the design of street light to low energy bulbs. My main concern to have the shine angled downwards to reduce light pollution. Some hippy chick neighbours are worried that it will confuse the trees and squirrels.

Thanks.

🐿🐿🐿

Fire · February 2021

This quite detailed article suggests the jury might be out on how much damage 'rich blue LED' might do to fauna. Nothing mentioned about plants. It does suggest that new LED street lighting is much more directional than old sodium lights, so that even if the streets may seem brighter, less light is escaping upwards, which should bode well for dark skies. It says that blue-ended frequency LEDs are much more efficient than other, warmer tones, which is why local authories have gone for those.

Alex Summers at Cambridge University Botanic Gardens suggests LED street lights don't put out the right part of the spectrum to affect plants.

Richard James of the RSPB says "There's currently very little evidence that streetlights are having a significant negative impact on our wildlife," with the possible exception of moths. Insects are attracted to lights and bats feed on the insects, but I don't think this is different with LEDs.

BobTheGardener · February 2021

The fact is that street lights are an unnecessary waste of energy. Studies show that there is zero reduction in crime when streets are lit compared to being unlit at night, and that 'crime' argument is the one relentlessly put forward by the lighting industry and a few badly informed members of the public as well as some police forces who don't look at their own figures. All transport is mandated by law to use onboard lights at night and motorized vehicle lights are more than adequate for the task (if they aren't, you're due a ticket.)

I've lost count of the number of cars driving around town after dark with no lights on because they 'can see quite well' in areas lit by street lamps, forgetting that the main reason to put your lights on is to inform others of the presence of your vehicle on the road.

Dovefromabove · February 2021

We‘ve had that type of streetlight here for several years ... I can see no difference in the wildlife’s behaviour or plant growth. However the lights on the sideroads are all turned off around midnight and don’t come back on until 5am ... lights remain on along the bus route. We live this system. Dark nights are great 👍

Fire · February 2021

Slight tangential to the question, Bob, but my older neighbours feel very unsafe walking around where the street lights are more shaded by the street trees. As a woman walking back through London at night, I'm glad for lighting, though I love very dark nights.

There have been more light efficient designs around for many years now, directing most of the light down rather than up and out. I hope those are now being more widely adopted. From aeriel views of the Uk, europe and the world, it would seem not.

Where I live, street lights are a given. The question is more - of what sort?

BobTheGardener · February 2021

As an amateur astronomer, I am very happy that many new street lights are aimed downwards, although the problem is that there is no adequate law to enforce this is done by the installers, and that needs to be addressed. I obviously understand the 'fear' argument and that will probably win the day, even if some of it is based on 'fake news', so to speak. Indeed, some folk are simply frightened by the dark and that is really a very complex psychological/social issue, but not one which I think can be easily addressed, so best assume street lights are here to stay in some situations. However, I want them to be properly specified and, above all, properly fitted (and this must include masking those which shine into peoples bedroom windows at night, because that is definitely linked with some types of ill health.)

Astronomers developed special light pollution filters which were fairly good at blocking the yellow light from sodium street lamps because that consists mainly of a single frequency of light. Unfortunately, LEDS produce a wider spectrum and such filters are not effective, so while there is less light being shone into the sky by LED fittings, what pollution there is is actually a little worse for us. On balance, I'd sooner we waste less energy, so LEDs it is.

B3 · February 2021

The back garden is well away from the led lights out the front yet it never really gets dark - just monochrome.

Fire · February 2021

Other issues and preferences aside, can I ask what people think about the odds of LED street lights seriously affecting tree growth?

steephill · February 2021

Some research findings here - https://www.researchgate.net/figure/The-spectral-output-of-LPS-and-LED-street-lights-representative-of-the-lights-used-in_fig2_299395983

It looks like the comment from Alex Summers about light spectrum isn't quite correct, LED street lighting is broad spectrum and does cover some of the wavelengths for photosynthesis. Specialist LED grow lights used in horticulture will have a better spectrum for plant growth of course.

punkdoc · February 2021

I know that Sheffield university are doing some research into the effects LED street lights have on nocturnal animals. I am not aware of any results they may have had.

BobTheGardener · February 2021

Because the intensity is so much lower than the sun, I suspect it will have little affect on growth. However, I am aware that photosynthesis requires a period of darkness for the chemical cycle to complete, so if the amount of light at night is just strong enough to prevent or degrade the efficiency of that stage, it would likely affect (suppress) growth rate. That would require quite a lot of research to test, I would think. Hopefully someone, somewhere, is on the case. I'll see if I can find anything.

LED street lights affecting plant growth?

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