Night-time satellite images of the Earth show a sea of light that stretches across populated areas around the globe. The electric light-bulb has come to represent economic prosperity and the advance of modern technology. But too much light can have a negative effect on the health of both humans and animals -- and scientists are warning of the dangers of light pollution. 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.