Check out this PBS documentary about the growth of electric light and the effects of light pollution.

[full film here]

“In the film The City Dark, filmmaker Ian Cheney describes light pollution as light reflecting off moisture and dust in the air, creating a glow in the sky. The most common cause of light pollution is over-illumination — streetlights and outdoor security lights that spill outward, billboard and landscape lights directed upward and businesses like convenience stores and gas stations operating with excessive light output. Though light at night has brought indisputable benefits, its excessive and unregulated use has been problematic. According to the Institute for Local Self-Reliance, each night almost one third of the light used outdoors escapes into the night sky, where, rather than providing useful illumination, it causes glare, sky glow and other types of light pollution. According to estimates from the International Dark-Sky Association, each year in the United States more than $1 billion dollars are spent to generate this wasted light.”