The increased sky glow which adversely affects the environment is called light pollution, for it originates mainly from excess light that does nothing to increase useful nighttime illumination. It is light that sprays horizontally and upward into the sky from poorly-designed lighting fixtures. It is light that glares into the eyes of motorists and home owners, compromising visibility, safety, and security. It is light that depresses property values by reducing the aesthetic quality of a neighborhood. In the United States and Canada over a billion dollars annually plus large amounts of energy are lost generating this wasted light.
Light pollution is a special threat to astronomy.
Many observations, including most of those of cosmological interest, can be made only from prime observing sites, remote from centres of population. Some older observatories, such as the David Dunlap in Ontario and Mount Wilson in California, are severely affect by light pollution from nearby urban centres. New observatories usually are located at remote sites, and amateur astronomers routinely drive large distances to escape the glare of towns and cities. The argument that all astronomy can be done from space is incorrect because it does not make sense to do in space, at much higher cost, what can be done from the ground. There are observations that can only be done from space, but more than three decades of space astronomy have greatly increased the need for ground-based observatories.