Mesmerised by Light

Mesmerised by Light

Every year in New York two beams of light reach into the sky from where the World Trade Center towers used to be. Each of the beams is powered by forty-four 7,000 watt xenon spotlights. The incredibly powerful lights are powered by biodiesel generators using cooking oil from local restaurants. Another concession the installation makes to the environment is that the lights are regularly turned off during the night to allow migrating birds trapped by the light to continue their journeys.

Simple solution

Migratory birds use the cover of darkness to travel and avoid predators. For reasons that are not fully understood they are mesmerised by the beams and circle endlessly in them. And it’s not just a few birds. Tens of thousands of them are attracted and, according to Dr Susan Elbin of the Audubon Society, “you can see the pillars of light sort of filling up with birds, almost like they’re pouring in from the top”. If the lights aren’t turned off some of the birds fly mindlessly within the pillars all night until they become completely exhausted and fall to the ground. Some are more likely to fly into buildings when the sun rises and releases them from the thrall of the lights. The solution is simple. The spotlights need to be turned off from time to time. The birds then disperse quickly and resume their migration. The whole process is monitored by volunteers for the Audubon Society (a prestigious US conservation organisation) who keep an eye on how many birds are trapped and tell the organisers when to switch off.

Special LEDs

The phenomenon of birds being attracted to lights has been observed from as far back as the nineteenth century with lighthouses often attracting thousands of wheeling seabirds. Another common problem is birds flying into lit skyscrapers. The easiest solution is to turn the lights off when they aren’t needed. But there is another way around the problem. On the island of Ameland off the coast of the Netherlands the LED streetlights are a peculiar blue-green colour. They have been specially designed so that they do not attract or disorient the migratory birds that fly over the island.

Blue-green future?

LED technology continues to become increasingly refined and tuned to its environment. A future in which the massively powerful xenon bulbs used in the Tribute in Light could be replaced with blue-green LEDs that don’t have to be turned off to let confused birds escape is possible. After all, the intense lights that originally caused the problem in lighthouses have given way to LED. But it’s probably easier to persist with switching on and off the older technology for such a brief commemoration than go to the huge trouble and expense of an experimental upgrade. After all, the birds get the chance to continue their migration either way.

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