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You know, if light were a drug, you might say that humans have become addicted. People have used artificial light to make the world a much brighter place. But brighter may not always be better, as NPR's John Hamilton reports.

JOHN HAMILTON: The thing about most places after dark is - they're not dark. I'm walking down a street in Washington, D.C. and there's light everywhere - headlights and stoplights and store lights. Even some Christmas lights. Is as if the entire society had decided to vanquish night.

Mr. ROGER EKIRCH (Virginia Technical University): Darkness oftentimes is viewed as a hindrance, perhaps as a nuisance

HAMILTON: Roger Ekirch is a historian at Virginia Tech in Blacksburg. He also the author of a history book about night. Ekirch says humans have spent hundreds of years, seemingly intent on turning night into day.

Mr. EKIRCH: The Russian government, barely a decade ago, tried to launch a giant space mirror which would have reflected the sun's rays, transforming night - in some portions of Russia - into twilight.

HAMILTON: And there's an Italian village in the Alps that actually does get extra light from a huge mirror on a nearby mountainside. Ekirch says all this lighting is taking away something that used to be an important part of human life: the privacy, anonymity, and freedom of truly dark nights.

Mr. EKIRCH: Milton wrote, 'tis daylight that makes sin. In other words, one was able to engage in all sorts of activity after dark that ordinarily would be preserved and would not be permitted during the day.

HAMILTON: And it wasn't just sex. Ekirch says that for many Southern slaves, night was the only time they could socialize or travel unsupervised.

Our brighter world also affects sleep patterns. Ekirch says the standard of eight continuous hours is a modern invention. He says before artificial light, Western Europeans slept in stages.

Mr. EKIRCH: The average person slept for three or four hours, awoke for an hour or more of quiet wakefulness, and then returned for a second round of sleep.

HAMILTON: That wakeful period provided a time to think, or pray, or ponder dreams while they were still vivid.

Artificial light also can affect hormones. For example, it can suppress the production of melatonin, which seems to affect both sleep and the immune system. Bob Gent is with the International Dark Sky Association, a group that's trying reduce light pollution.

Mr. BOB GENT (International Dark Sky Association): There's all kinds of research going on now about the impact of melatonin suppression. What is it doing to the human immune system? Can this be one of the reasons why people living in bright cities, at night, you know, have a higher incidence of breast cancer, etc.

HAMILTON: But Gent says that perhaps the most important thing about darkness is what it allows us see. He remembers growing up in Phoenix in the 1950s, before the city had so many lights.

Mr. GENT: You could go in the backyard, look up and just be overwhelmed by the beauty of the night sky. And as a boy I was asking questions like, how many stars are there? How far away are they? What are they made of? Can we visit them?

HAMILTON: Today, Gent lives in the southeast corner of Arizona, in a town called Sierra Vista. He and his wife built their house in a spot that's so dark at night, you can still see the Milky Way.

Jon Hamilton, NPR News.

INSKEEP: And you can see a NASA image showing just how bright the Earth is at night by going to our Web site at NPR.org.

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INSKEEP: It's MORNING EDITION from NPR News.

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