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Dark Sky Movement

The dark-sky movement is a campaign to reduce light pollution. The advantages of reducing light pollution include an increased number of stars visible at night, reducing the effects of electric lighting on the environment, improving the well-being, health and safety of people and wildlife, and cutting down on energy usage. Earth Hour and National Dark-Sky Week are two examples of such efforts.


The movement started with professional and amateur astronomers alarmed that nocturnal skyglow from urban areas was blotting out the sight of stars. For example, the world-famous Palomar Observatory in California is threatened by sky-glow from the nearby city of Escondido and local businesses. For similar reasons, astronomers in Arizona helped push the governor there to veto a bill in 2012 which would have lifted a ban on illuminated billboards.


Nocturnal animals can be harmed by light pollution because they are biologically evolved to be dependent on an environment with a certain number of hours of uninterrupted daytime and nighttime. The over-illumination of the night sky is affecting these organisms (especially birds). Light pollution has also been found to affect human circadian rhythms.


The dark-sky movement encourages the use of full-cutoff fixtures that cast little or no light upward in public areas and generally to encourage communities to adopt lighting regulations.

Dark Sky Lighting

Dark-sky lighting is a concept important to the dark-sky movement, as it minimizes light pollution. The concept was started in the 1950s by the city of Flagstaff, Arizona. Flagstaff is a city of over 70,000 people, but because of its effectively controlled lighting, the skies are dark enough to see the Milky Way, and the light dome over the city viewed from some distance has been measured as less than 10% as bright as that over a similarly-sized city (Cheyenne, Wyoming) that has not sought to protect its night skies. Lights should be shielded on the top and sides so light doesn't go up to the sky and only used when needed (use motion detectors and only the wattage necessary). To minimize the visual brightness of skyglow and reduce glare and most other biological impacts, amber-colored lighting is critical (such as formerly high- and low-pressure sodium, or now amber LED). The International Dark-Sky Association certifies fixtures as dark sky friendly, and these will have the IDA Fixture Seal of Approval.

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