“Light at night is now clearly a risk factor for breast cancer. (...) Breast tumors are awake during the day, and melatonin puts them to sleep at night.”
David Blask, researcher at the Cooperstown, New York-based Mary Imogene Bassett Research Institute.
To reduce the risks specialists recommend a good night of sleep with all light sources blocked, both from outside and inside. This means shades closed, TVs and monitors off, lamps, and everything else that's lit enough to be a substitute for daylight.
The light bill for all of this night town lights is huge. Estimates show 1.5 billion dollars of wasted energy worldwide and more than 10 million tons of carbon dioxide produced. In a world running mostly on oil and looking for alternative energy sources, this is completely unacceptable.
The Globe at Night project is a project that aims at measuring light pollution all over the planet, and it relies on common people to input their observations. It's as simple as going out for some minutes at night and looking for the Orion constellation, and comparing your observations to the examples given in the website to measure which magnitude stars can be seen from your location. Head over to their website and give your contribution.