Light Pollution

     From CNET...for a third of humanity, it's obscured by fog of light, caused by the artificial illumination used at night in towns and cities. And for Americans, it's even worse: Around 80 percent of the country can't see the Milky Way at night. "We've got whole generations of people in the United States who have never seen the Milky Way," said Chris Elvidge, a scientist with NOAA's National Centers for Environmental, who co-authored an update of a global atlas of light published in the journal Science Advances. "It's a big part of our connection to the cosmos -- and it's been lost." They discovered that it's most prevalent in Singapore, Italy and South Korea, while Canada and Australia are the darkest (although it's worth noting that most of Australia's population is concentrated around its edges). You can play with an interactive map to find out how heavily your home is light polluted HERE.
     Less than 100 years ago everyone could look up and see the Milky Way, but now increased and widespread use of artificial light is impairing our view of the sky, adversely affecting the environment, causing safety issues and affecting energy consumption and even health. The inappropriate or excessive use of artificial light can have serious environmental consequences for humans, wildlife, and the climate. Types of pollution:

Glare – excessive brightness that causes visual discomfort 
Skyglow – brightening of the night sky over inhabited areas Light trespass – light falling where it is not intended or needed 
Clutter – bright, confusing and excessive groupings of light sources 

   Light pollution is a side effect of our civilization. Sources include building, both exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. Much outdoor night lighting is inefficient, too bright, poorly targeted, improperly shielded and, in many cases, unnecessary. Both the light and the electricity is wasted by spilling it into the sky, rather than focusing it on what is intended to be illuminated. Artificial lights overpower the darkness causing cities glow at night which disrupts the natural day-night pattern and shifting the balance of the environment. 
     The negative effects of the loss is very real. It leads to:

Increased energy consumption
Disrupting the ecosystem and wildlife
Harms human health
It has an effect crime and safety

    There is evidence that artificial light can alter physiology, including hormonal balance, as well as behavior, orientation, organism fitness, food web interactions, and biotope connectivity. The artificial disturbance of the natural day/night cycle may, as a result, have serious psycho-physiological and even medical consequences for humans, along with ecological and evolutionary implications for animals, plants, and even entire terrestrial, freshwater, and marine ecosystems.
    Street lighting has been blamed for up to 50 percent of the urban sky glow due to 95 percent of the light directed down toward the pavement being reflected upward at reflectance rates ranging from 6 percent for asphalt to 25 percent for concrete. Urban sky glow has been reported to be increasing around 30 percent annually in some American cities
     Long-term exposure to artificial lights can prevent trees from adjusting to seasonal changes, which has an impact on wildlife that depend on trees for food or shelter.  Artificial lights also have a devastating impact on birds. There are over 200 bird species that follow nocturnal migratory patterns across North America, but the sky is lined with communication towers and skyscrapers. Lights confuse the birds and cause them to crash into buildings. Seriously! It's estimated that the New York City skyline kills 10,000 birds per year and one billion die from collisions across North America alone. 
     Even turtles are impacted by artificial lights. Some sea turtle hatchlings born at night follow the moon’s reflection on the water to find the ocean, but now big cities along coastlines confuse them and they head inland by mistake. 
     How bad is light pollution, really? Los Angeles experienced a full blackout in 1994 and people reported a strange, silvery cloud over the city; they were seeing the Milky Way for the first time. 

5 Appalling Facts about Light Pollution