End of the Night
From amoeba to human, nearly all living things run on an internal clock, a circadian rhythm that regulates our respective business over a 24-hour period. It's nature's way of optimizing the day: when best to spawn, lay, hatch, bloom, croak, sing like a robin, or (if you're a copepod) migrate up to feed on algae in the watery light. The clock mandates rest, too; there's a time to close, to be silent, to sink into the murky depths and hide. Day, and night, are inscribed in us.
But what if night stops coming, if daylight lasts all day? Stargazers already are seeing it. The illumination from streetlights and other artificial night lighting is now so persistently bright that 10 percent of the world's population, and 40 percent of Americans, no longer view a night sky that the human eye perceives as fully dark. It's a scientific loss for astronomers and a psychic one for the rest of us.
More and more, ecologists are finding that this false light also takes a toll on the natural world. Every year, night-migrating birds collide with bright buildings by the millions. Field studies have shown that artificial light changes the spawning times of certain species of coral and fish whose reproductive cycle depends on a lunar clock. It washes out the mating signals flashed by fireflies. One scientist found that a group of tree frogs halted their mating calls whenever the nearby football stadium held a night game and caused the sky to glow.
Insects are perhaps the hardest hit. The clouds of bugs that flock to streetlights may be a boon to bats, but the effect is likely temporary. A study in Germany found that the lights around new gas stations attracted swarms of insects for the first two years, after which their numbers fell precipitously because all the bugs nearby, and any eggs they would have laid, had been effectively sucked out of existence. "Lights have a remarkable vacuum effect," says Christopher Kyba, a physicist at the Free University in Berlin. Insects are critical to ecosystems -- tasty morsels in the food web and often, as with moths, key pollinators of plants -- so ecologists are left to wonder about the long-term impact of the phenomenon on flora and fauna.
Kyba is an active participant in Verlust der Nacht ("loss of the night"), an ongoing endeavor by several institutes in Germany to explore the impacts of what's becoming known as ecological light pollution. But as Kyba and his colleagues recently discovered, the underlying problem -- the manifestation of the light itself -- is more complex than anticipated. For months, using devices called sky quality meters, they measured the brightness of the night sky over Berlin and nearby rural areas. The results were dramatic: in the city, clouds made the sky 10 times brighter than it would have been on a clear night, and five miles outside the city it was nearly three times brighter. "Some people might say, 'Well, everyone knows it gets brighter under cloudy conditions,' " Kyba says. "But now we know how much." And the scale of the amplifier effect suggests that ecologists need to start taking it into account, given that many animals take their cues from moonlight or its absence. Until now, efforts to reduce light pollution have been led by astronomers, who have illustrated the problem with satellite photos of night-blazing cities. But satellite data may tell only part of the story. "For ecologists around the world, cloudy nights are more important than the clear ones," he says.
One can't do much about clouds, of course, so solutions to light pollution typically aim at the lighting. "There's a lot of room for improvement in the technology," Kyba says. For instance, replacing high-pressure mercury bulbs in rural road lights with high-pressure sodium bulbs can reduce their appeal to moths by 50 percent to 75 percent. Low-pressure sodium bulbs would draw even fewer insects, but they're monochromatic, which could disorient salamanders that rely on color cues to find their home ponds or frogs that consider coloration when selecting a mate. Newer LED streetlights can be dimmed to as little as 20 percent of their maximum brightness. But the spectrum of LED lamps is different from that of the lamps we're using, Kyba says, "so it's an open question whether that's better or worse for animals."
But bulbs are the least of it. The place to start, Kyba says, is "to encourage maximizing useful light and minimizing light that no one uses." Step one: make sure that most outdoor lights are shielded so they don't radiate directly into the sky. "Globe lights, while admittedly pretty, are probably among the worst offenders," he says. Architectural and advertising lights could be flicked off after a certain hour.
What's called for is darkness: less of the light we disregard anyway, except, increasingly, to rue it. We're bright people -- too bright; surely we can figure this one out.