Night-time satellite images show a sea of light that stretches across populated areas of the Earth. But too much light can have a negative effect on the health of both humans and animals
At night, city lights kill large numbers of insects, confuse migrating birds, and rob many people of a good night's sleep. Humans have developed their day / night cycle over millions of years -- a cycle that dictates that people work during the day, and relax in the evening. Now, researchers are working on next-generation lighting systems that are more sustainable and work more efficiently.