14 Streetlights

Introduction to Light Pollution

When most of us step out on a clear, moonless night and look up, we see… few stars. Many people in industrial or “advanced” countries have never seen the Milky Way, our own home galaxy. And in some large cities, one is fortunate to see the Moon, bright planets, and the brighter stars. Yet, this has not always been the case.

For many centuries, people from around the planet looked up in fascination at the night sky. They passed along stories about the groupings of stars they saw; only the Moon was bright enough to cause fainter stars and the Milky Way to not be visible. And, since the Moon went through its phases, night time darkness would return. So, natural light pollution does occur. You can really see the effects of a bright moon while trying to locate some of the faint constellations or watch a meteor shower. The sky is simply “washed out” by moonlight.

The Earth’s moon is shown.
The bright light of the full moon [ “Hazy Moon With Clouds” by Lynn Greyling is in the Public Domain, CC0]


Streetlights first appeared about 300 years ago as oil lamps. These oil lamps, often mounted on wooden poles or cast-iron fixtures by the early 18 th century, continued in use until the early 19 th century, when gas lamps came into use. By the 20 thcentury, electric lighting was in use. Today outdoor lighting is used for a number of reasons:

  • Streetlights; roadway lighting
  • Security
  • Buildings
  • Advertising
  • Ornamental and Decorative (1)
Dots of light across the globe are shown where larger cities are located.
The Earth at Night — a worldwide, cloud-free mosaic showing the extent of lighting. The image was taken during 2016 by the Suomi National Polar-orbiting Partnership satellite. [ “BlackMarble20161km” by NASA Earth Observatory images by Joshua Stevens in the Public Domain ]


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