As more of us live in cities, the question of light pollution is becoming increasingly topical and important to address. There seem to be three main causes, and also two key solutions which we could take to lessen the problem. The main cause is almost certainly the use of lighting for advertising in public spaces. For example, if we look at cities such as Tokyo or Moscow, almost all available surfaces are fitted with some form of light, often for announcements or commercial use. This huge expansion in illuminated advertising is partly a result of competitive pressures, and also due to the power of such advertising, with flashing lights, video and pictures. A secondary cause is the large number or street lamps and security lights used in cities, which are intended to reduce accidents and crime by removing shadow areas at night. Finally, high levels of night-time traffic also produce light pollution, as drivers use headlamps which shine into windows and gardens after dark. Turni...