LED streetlights reduce insect populations by half

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Over the last decade, there has been a transition in the UK’s streetlights.

Councils have replaced mercury and sodium streetlights with white LEDs, arguing that they use half as much energy and are easier to control. Durham County Council began this work in 2013 by upgrading over 55,000 streetlights across the county in a move that the council claimed would save over £24 million in a 25-year period.

Given the current climate crisis, it sounds like the type of policy that would go ahead unopposed; who could say no to reducing energy consumption?

But nothing is ever that perfect. The rollout of LEDs has been problematic from the beginning, with Public Health England warning in 2018 that the new streetlights, which release higher levels of blue light, might disrupt our sleep patterns and cause damage to our retinas.

The new streetlights, which release higher levels of blue light, might disrupt our sleep patterns

Councils were asked to think beyond immediate financial benefit and consider the social costs of installing these new lights. However, the transition continued unabated.

Light pollution harms wildlife. Animals depend on the daily rhythm of light for essential behaviours (eating, sleeping, reproduction, etc.). Introducing artificial lighting confuses these behaviours. Birds, for example, can end up migrating too early or too late because of the changing light conditions in their habitat, and bright lights can attract insects.

So it is unsurprising to learn that LEDs are having a negative ecological impact. Research published by Boyes et al. last August makes clear the exact severity of this impact, with insect populations reduced by up to a half.

Acting as the basis of most food chains and playing an essential role in controlling soil ecosystems, the impacts of their loss could be significant, with consequences further up the food chain. Caterpillars, for example, are a key food source for hedgehogs and songbirds, and later become as important pollinators as moths.

Funded by the National Environment Research Council, the scientists behind this latest study claim it to be the first investigation into the impact of white LED lights on insects. The researchers focused on moth caterpillars for this study because of their abundance and low mobility.

Populations of moth caterpillars were 52% lower than in nearby, unlit areas

Studying hedgerows located under LED streetlights, populations of moth caterpillars were 52% lower than in nearby, unlit areas.

In contrast, populations under sodium lighting were 41% lower. The researchers considered moth caterpillars to represent other nocturnal insects, implying that the effect of LED lights goes beyond one species.

The obvious question is whether this rollout of LED lights should continue. Although they are having a greater impact on local wildlife, it’s also important to remember their greater energy efficiency in the context of climate change, and the enhanced public safety that the brighter LEDs can provide.

However, there is a solution. LEDs are far easier to customise than mercury or sodium. It is possible to dim them or apply filters that block the blue light, which is the most harmful both to insect populations and to our sleep patterns.

Placement is also important. Boyes et al. argue that certain key habitats ought to be left alone, and that streetlights in general ought to be used with consideration of the surrounding environment.

Given the seemingly eternal paralysis around the climate, it’s refreshing to have an environmental issue with a seemingly easily achievable fix. Compromise is key with environmental issues, and the suggestions given by the researchers are certainly worth considering.

With this study and hopefully future ones like it, local governments can have an array of information to make the best decisions about the future of street lighting.

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