The earth at night as viewed from a space, in a composite image from NASA.
The world is not as dark as it used to be. Streetlights, parking lot security lights, office building lights, and neon signs shine all through the night. Light pollution can come directly from light bulbs, or it can bounce off of dust and water droplets in the air, creating a bright haze called skyglow. This 24-7 illumination can be seen from space, and it has negative effects on humans and wildlife. But there are ways to dim the lights and reduce their effects—and save energy in the process.
Astronomers have long aware of the problems associated with nighttime illumination—it makes stars disappear. Big telescopes are built away from big cities for this reason, although bright lights have a way of encroaching. QUEST blogger Ben Burress talks about light pollution and astronomy here and here.
Non-astronomers are affected by nighttime lighting, too; exposure to light at night affects our circadian rhythm, the 24-hour cycle deep inside our bodies. Seeing light at night can cause sleep disorders. And long-term exposure to light at night has been linked to breast cancer, because light inhibits the production of melatonin, which slows the growth of cancer cells.
Exposure to light affects animals, too. Anyone who has sat next to a porch light on a summer evening knows that moths are drawn to light—along with a multitude of other insects. Outdoor lights disturb insects’ nighttime navigation, and affect their feeding and mating. Lizards are often found feeding on the tasty insect snacks that gather around lights. Often, these lizards are not normally nocturnal—staying up at night gives them access to a “night-light niche” and an abundant food source. It also creates the opportunity for interactions between animals that would never meet in the dark conditions of previous centuries. Some lizards get a double benefit, basking in the warmth given off by artificial lights (incandescent lights are really inefficient; most of the energy they use goes to producing heat, not light).
Night lights make birds sing at odd hours, and mess with their mating and migration schedules. During migration, birds are drawn to the light from tall buildings and towers, resulting in deadly collisions.
Sea turtles are perhaps the most famous example of animals affected by light. Hatchlings swim towards the light—historically the horizon above the ocean. But now that beaches are backed by well-lit condos and hotels, baby turtles crawl further onshore instead of out to sea. There is evidence that sea turtles are drawn to light with short wavelengths, and using bulbs with longer wavelengths or using filters that cut out short light wavelengths reduces the number of baby turtles crawling in the wrong direction.
Simple fixes, like different bulbs or shades that focus light on the ground, can do a lot to re-darken the night sky, as does turning off unnecessary lighting. Dimmer, more efficient bulbs that provide enough light for human needs—but not too much—are a step in the right direction, and can save on energy costs. Dark sky conservation and stricter lighting ordinances will help.
I was surprised by the negative health effects of exposure to nighttime lighting—something to keep in mind as I work late into the night, basking like a lizard in the glow of my computer screen.