International Dark-Sky Association

The International Dark-Sky Association (IDA) is a United States-based non-profit organization incorporated in 1988 by founders David Crawford, a professional astronomer, and Tim Hunter, a physician/amateur astronomer. The mission of the IDA is "to preserve and protect the night time environment and our heritage of dark skies through quality outdoor lighting."Light pollution is the result of outdoor lighting that is not properly shielded, allowing light to be directed into the eyes and the night sky. Light that shines into the eyes is called glare and light shining into the night sky above the horizon causes skyglow. Lighting can also cause light trespass when it is directed into areas that it is not wanted, e.g., a neighbor's yard and windows. IDA was the first organization in the dark-sky movement, and is currently the largest.

IDA's principal approach is to raise awareness about the value of dark, star-filled night skies and encourage their protection and restoration through education about the problems and solutions, including outdoor lighting practices that create less light pollution. In 2011, the organization had about 5,000 members in 70 countries.

Among many concerns, IDA and related organizations are collating research on light at night's (LAN) effects on human health and ecology as a result of artificial light at night. The hypothesis is that humans have evolved over millennia exposed to roughly equal periods of light and dark. The disruption of this circadian rhythm can cause hormone imbalance in all living organisms. In the last century, artificial lighting has reduced the regular period of darkness and may negatively impact health. Light at night has been linked to increased incidence of hypertension, attention deficit disorder, obesity, diabetes and some forms of cancer.

...
Wikipedia