Skyglow in Mexico City

I used to go for a walk every night. It was a pleasant habit—exercise, fresh air, quiet time alone to think. I made a point, whenever possible, of walking in an area away from the city lights, where the sky was dark enough that I could get a good look at the stars. I knew how to pick out some of the constellations, though I could never quite understand how anyone could see a goat or an archer in the patterns of stars. Seeing shapes in clouds is one thing, but mentally connecting the dots to form a complex picture didn’t really work for me. That’s not to say I didn’t see anything in the stars, though. As I looked at a particular star, I would think about the possibility of life in outer space, the chance that a planet circling that star may be home to people like me—or unfathomably different beings. I’d think about how Earth is just another one of those countless planets and the sun just another one of those countless stars. And picking my favorite star of the moment, I’d say to myself, “Someday I’ll find a way to go there.”

Looking at the stars and thinking about them in this way always had a calming effect on me. I felt as though it gave me a sense of proportion, that it put my own crises and ambitions in perspective. It didn’t make me feel insignificantly small; instead, it made me feel somehow privileged to be able to see and understand what may be out there, and to realize I’m a part of something so big.

The Stars at Night Aren’t Big or Bright

Nowadays I don’t notice the stars very often, and when I do, I don’t usually think about them as I once did. But every now and then, I’ll be on a trip to a remote place—an island, a desert, a rural getaway somewhere—and again the stars will catch my attention. Invariably I’ll wonder why I hadn’t noticed them in so long. Is it just that I’m older and busier? That may be part of it, but a bigger part is that the lights of the city often make it very hard to see the stars, always focusing my attention on the surface of my own planet. This is one consequence of the increasing problem of light pollution.

The term “pollution” is apt because excess or unwanted light can be an irritation or even a safety hazard. Like air pollution, light pollution is typically a by-product of machines and devices that were intended to make our lives easier, more convenient, and safer. Another similarity is that light pollution can be reduced greatly with careful attention to design. But because most people have become accustomed to light pollution as a fact of life, there is usually little incentive to worry about it when designing or purchasing lighting products.

It Was a Bright and Stormy Night

The most frequently discussed manifestation of light pollution is a phenomenon called skyglow—a layer of glowing air that obscures anything beyond it. Skyglow occurs because the atmosphere itself diffuses the light; the effect is strongest when lights point upward, and it’s exacerbated by moisture, pollution, and dust. If you ever look up into a clear night sky in the city and find that very few stars are visible, skyglow is the culprit. The effect is even more striking from a distance; if you’re outside the city in a darker area, you can often see skyglow as a glowing haze over the brightly lit area, even if the lights themselves are not visible.

There are other forms of light pollution as well. The term light trespass is used to describe light that shines onto someone else’s property. This can be a neighbor’s floodlight that shines into your backyard, for example, or a streetlight that shines into your window at night. Another type of light pollution is glare, a general term describing any kind of light that impairs or obscures one’s vision. Glare interferes with the eyes’ natural ability to adapt to lower light levels at night, and can pose a serious safety hazard—especially for drivers.

I Wear my Sunglasses at Night

Astronomers—both professional and amateur—have always found light pollution to be a serious problem. But stargazers are not the only ones affected. Biologists are increasingly concerned that light pollution is detrimental to wildlife—disrupting natural biological cycles, interfering with the hunting and feeding behaviors of nocturnal animals, and hindering the navigation of migrating birds. Humans may be directly affected as well: studies have suggested a connection between the use of electric lights at night and an increased risk of breast cancer. Even relatively small amounts of light reaching the eyes during sleep can throw off natural circadian rhythms, altering the body’s production of the sleep hormone melatonin and potentially leading to a variety of health problems.

Light pollution is a solvable problem. The basic principle is to use light at night only where and when it’s actually needed, and only in the amount needed. This may involve shielding light fixtures so that light is directed downward (and away from adjacent properties), putting lights on timers or motion-activated switches, or using lower-wattage bulbs. There’s also the radical notion of turning off outside lights at night. According to conventional wisdom, more light equals more safety, so presumably brighter places should have less crime than darker ones. But surprisingly, this is not necessarily the case. Several school districts, in an effort to save money on electricity, tried turning off outside lights on schools and playgrounds at night and found, counterintuitively, that vandalism rates plummeted. That’s not to say you should start walking down dark alleys at night, but then, I suppose even criminals need to be able to see what they’re doing.

Reducing light pollution is in some ways at odds with modern Western culture—especially when it comes to outdoor advertising and other commercial lighting. And no one is arguing that cities and towns would be safer or better places to live if the streets were completely dark. But even while we teach our children not to be afraid of the dark, we do our best to surround ourselves with light. Perhaps a bit more darkness wouldn’t be such a bad thing. It could turn out to be healthier and safer, not to mention providing some much-needed perspective.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on July 28, 2003, and again in a slightly revised form on July 19, 2004.

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