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Ella McSweeney: How energy-efficient LEDs are disrupting animal life and blinding us to the night sky



With an intense darkness around me, I stood in a field in Roscommon one night last weekend and looked upwards to appreciate what was on offer: a dazzling, celestial display of exceptional clarity. It was a spectacle of starlight.

Just a few hours earlier, I had walked through Dublin city to Heuston Station under the familiar hazy glow of artificial lights that radiated upwards, forming a veil across the sky which obscured the starry night beyond.

On the train, I checked a world light pollution map and read about “zenith sky brightness” ratio, which is the ratio of the brightness of the sky directly overhead (the “zenith”) to the illumination of the sky at some angle away from it. The smaller the ratio, the higher the light pollution. These areas on the map are coloured pink and red; unsurprisingly, the greater Dublin area (along with all our other major cities) stood out.

Since the first incandescent light bulb was invented in the 1870s, artificial light at night has extended the working day, heralding a new era in how humans have radically shaped the dark. For millennia, creatures – including humans – have synchronised their lives with the natural dark and light cycle. Artificial light hasn’t just dimmed the night sky from view; it has also knocked out circadian rhythms, disrupted and disorientated migratory journeys, and lit up species to predators. It negatively affects birds, mammals, insects, crustaceans, fish, plants and even microbes, and most of the planet’s most important wildlife areas are now affected by light pollution.

In 2016, scientists estimated that over 80 per cent of the world’s population lives under light-polluted skies. Over the past decade, scientists say the average night sky has become brighter each year by just under 10 per cent. The rate at which this happens is equivalent to doubling sky brightness every eight years.

A significant culprit is the use of bright, cold-white LED (light-emitting diode) lights. LEDs are energy- and cost-efficient, but white LEDs contain high proportions of short wavelength blue light, causing substantial biological impacts. It fools the brain into thinking it’s daytime, causing disrupted sleep patterns, which can lead to a variety of chronic health conditions.

In a study of light pollution last year, scientists said that Ireland is particularly vulnerable to blue light pollution due to our recent transition to LED lights. In Dublin city, for example, the council oversees 47,400 lights and approximately 25 per cent of them are LEDs, but this is due to rapidly increase under the council’s Public Lighting Upgrade Project.

Unlike many forms of pollution, light pollution is reasonably easy to fix. If you switch off the light, the pollution stops. If artificial light is required, then there are LED light alternatives which are less damaging; for example, the use of warmer tones, such as red, that minimise the negative impacts to life.

For nearly all of human history, the stars have blazed brightly in the night sky. It wasn’t long ago when you’d have seen the Milky Way over most of our cities

An example of what is possible is the story of the starlings under Lagan Bridge in Belfast city. After their murmuration at dusk, thousands of them descend under the darkness of the bridge to roost for the night, hidden away from predators such as peregrine falcons.

One evening in February 2021, ecologist Conor McKinney stood on the greenway path on the side of the bridge and waited for the starlings to arrive. He had last been there in 2019 when the birds had darkened the skies and filled the air with swishing sounds.

But that night, Conor spotted just a dozen or so starlings. As he watched the arches, hoping in vain for more birds to appear, he noticed something new: the bridge had been, he said, ‘lit up like Las Vegas’.

Beginning in 2019, to save money, Northern Ireland’s authorities began to switch from yellow sodium street lights to LED alternatives. On the Lagan Bridge, the lights inside the old street lanterns that bordered the bridge were replaced with bright white LEDs. Beside the bridge, a derelict green area called Ravenhill Rest was set to be transformed into a public space for people to sit and watch the murmurations. A new seating area with LED lanterns at each corner – decorated with starling images – had been proposed. Underneath and to the side of the bridge, white lights shone bright in the night.

In a bid to dim the bridge once again, Conor decided to talk to the authorities. The Lagan Weir authority, responsible for the lights on the side of and underneath the arches, decided to put a red filter on the lights. This colour is less disruptive to wildlife. They also installed ‘on/off’ switches so they were easily controlled. He asked officials at the Department of Infrastructure to put blackout shields on the riverside lanterns to prevent light from spilling over the bridge. Finally, he asked staff at the Department of Community, responsible for the Ravenhill Rest, to amend their design so that the lanterns were capped. They agreed.

So far this winter, starling numbers are up. And while correlation is not causation – without scientific research, it’s impossible to confirm a direct link between the disappearance of starlings and an increasingly glowing bridge – it is likely that the bridge is once again a haven for the birds, allowing them to roost for the night, safe from predators.

For nearly all of human history, the stars have blazed brightly in the night sky. It wasn’t long ago when you’d have seen the Milky Way over most of our cities. The good news is we can do our bit to protect the night. If you, or your local school or sports club, use outdoor lighting, consider minimising what is needed; direct lights downwards and shield them; and use only LEDs with amber/red tones. Where possible, embrace the night and switch off. The wildlife around you will benefit, and if you look up, you might be awestruck at what shines through.

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