Excessive light at night -- especially blue-rich white light -- is bad for your health: it suppresses production of melatonin, leading to disrupted sleep cycles and elevated rates of serious diseases from diabetes to cancer.
Glare from poorly shielded lights shines sideways into private yards and houses, and can temporarily blinds road users. Glare makes visibility worse, not better, and can even provide dark shadows for intruders to hide.
Light should be directed down only, not out or up.
All animals -- including humans -- need darkness at night. 80% of mammals are nocturnal, and light pollution disrupts their feeding, mating, and migration. Millions of birds each year die when they become disoriented by bright city lights and crash into buildings or fly off course. Entire species such as the fireflies in this backyard in Northampton are threatened with extinction because of light pollution.
The naturally dark, star-studded sky is a priceless gift of Nature. The National Park Service considers dark skies a natural resource, like clean air and clean water, that must be preserved for everyone. Yet today, because of light pollution, most American children have never even seen the Milky Way, our galactic home.
Cities that control their light pollution can bring back the wonder and beauty of the stars for everyone to enjoy.
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