turn those lights "down"

From Ben Harder in U.S. News & World Report...

The night is not what it was. Once, the Earth was cast perpetually half in shadow. Man and beast slept beneath inky skies, dotted with glittering stars. Then came fire, the candle, and the light bulb, gradually drawing back the curtain of darkness and giving us unprecedented control over our lives.

But a brighter world, it is becoming increasingly clear, has its drawbacks. A study released last month finding that breast cancer is nearly twice as common in brightly lit communities as in dark ones only added to a growing body of evidence that artificial light threatens not just stargazing but also public health, wildlife, and possibly even safety.

Those findings are all the more troubling considering that an estimated 30 percent of outdoor lighting—plus even some indoor lighting—is wasted. Ill-conceived, ineffective, and inefficient lighting costs the nation about $10.4 billion a year, according to Bob Gent of the International Dark-Sky Association, a nonprofit that aims to curtail light pollution, and it generates 38 million tons of carbon dioxide a year....

People who are working while others are stargazing may face the greatest risks. Hormonal disturbances triggered by nighttime exposure to white or bluish light can disrupt circadian rhythms and fuel the growth of tumors, experiments show. Two decades of research indicate that women who work night shifts have unusually high rates of breast cancer, and some data suggest a parallel effect on male workers' prostate cancer rates. Last December, a unit of the World Health Organization deemed shift work a probable human carcinogen.

The second sentence sounds like good research-- looking at the causal effects of disrupting circadian rhythms rather than the correlations between health and those who work night shifts. The difficulty with this sort of (common) research is distinguishing between the likelihood that those who are more likely to get cancer (e.g., because they are poor or live in an urban environment) are also likely to work night shifts or live in cities.

Light beamed into the sky is squandered, since it's not illuminating any target. Yet many fixtures—like old-fashioned spherical streetlamps—send plenty of photons upward and outward. "If you fly into a city at night and you can see the streetlights from the airplane," says Chad Moore, leader of the National Park Service's Night Sky Program, "that light is counterproductive."...