White light white heat

A GROUNDBREAKING study from Butterfly Conservation in 2021 highlighted the fact that street lighting reduced the abundance of moth caterpillars in grass verges by 33% and in hedgerows by 43% compared to a comparable unlit roadside habitat and that the use of LED street lighting had an even bigger impact with populations reduced by 52% in hedgerows and 43% on grass verges. The three year research project carried out by PhD student Douglas Boyes was the first real world study to show the negative impacts of light pollution on moth populations.

With the logistics industry’s tendency towards 24/7 operation and the near ubiquitous use of LED lighting both inside and outside facilities to reduce power consumption and costs, this seems to be a case of good intentions and unintended consequences.

I picked up the phone to Butterfly Conservation’s head of science Richard Fox looking to see if there was any way the impact of lighting, and using LED lighting in particular, could be easily mitigated without impacting operations.

“We are only just understanding the scale of the problem, there are tonnes of studies about why moths and night pollinators are attracted to artificial light but nothing linking its possible effects on moth life cycles for example stopping adults from feeding or releasing sex pheromones etc, but it is a big jump scientifically and logically to say that just because attracted to the lights that that it does bad things to them.

“It does leave them more exposed - entomologists even 100 years ago noted that bats and birds would hunt around street lights. The study we did set out to establish a link to real world lighting and insect populations and because it focused on the moth caterpillars and not the adult moth it showed there was a substantial negative impact on the population particularly by LED street lights.

“Regarding logistics sites and in particular illuminating concrete yards [where there are no hedges and verges] is not going to have a dramatic effect on bio diversity per se. I am more worried about the areas surrounding it the habitats created in association with these  sites which may then be lit or subject to lighting overspill not only reducing the potential benefits of BNG compared to if it was not lit but also attracting insects from non lit habitats outside the site where predation will be higher and matings fewer, in effect potentially creating an ecological sink.

“What can you do? Limit the light that reaches these habitats. If it doesn’t need to be lit, don’t light it and if it does need to be lit, does it need to be lit all the time? In parts of Europe, they are installing motion activated street lighting. Partial lighting or motion activated lighting on a site, which is them only lit when there is an activity and goes off when the activity ceases would be beneficial.

“Less lighting is the key and most obvious, but directing where a light shines and making sure lighting is directed only where it is needed and not anywhere else which is done with screens round the light fitting on street lights is both environmentally and economically beneficial.

“The next possible thing to do would be to alter the colour of the lighting. We know moths and others are more strongly attracted to light at the blue end rather than the red end of the spectrum. Don’t use broad spectrum white light, use those that are warmer tone. The warmer you make them the better. Technically, you can alter the frequency of light that LEDs produce. The transition may cost but it will be no more expensive to run operationally nor is it more expensive to install at the outset.

“A lot of LED lighting emits UV which humans cannot see but which is very attractive to night time pollinators. I would encourage anyone installing outdoor lighting to avoid UV LED light.”