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How Does Light Pollution Hamper Our Ability to See the Night Sky?

Light pollution is a growing problem around the world, as the population increases and nighttime activity in urban centers intensifies. Light pollution radically alters the view of the night skies. In the wilderness at night, millions of stars are visible and the Milky Way can be clearly seen. But in the biggest cities, just a handful of stars are bright enough to outshine man-made light pollution.

Poorly Designed Lighting
- Outdoor lighting is necessary for safety and convenience, but many of the fixtures in use today are poorly designed. They do not direct all of the light downward where it's needed but allow as much as 30 percent of it to escape upward into the night sky, where it can have harmful effects.
Sky Glow
- Light escaping upward into the atmosphere bounces off air molecules, moisture and dust and is reflected back to your eyes. This is the phenomenon known as sky glow, which is most pronounced in urban centers. This interference from other light in the atmosphere cuts down on your eyes' ability to perceive stars. The stars are in effect "washed out."
Physical Effects
- Misdirected or overly bright lights also have a physical effect on your eyes. Your pupils contract to cut down on the amount of light let into your eyes. This affects your ability to pick out more faint light from the stars, because your eyes are not "dark-adapted."
Astronomy
- Professional stargazers--astronomers--find their work increasingly hampered by light pollution. It goes beyond having their view of the stars obscured. One of the ways astronomers conduct their research is to split apart the different types of light, visible and invisible, being emitted by distant objects such as other galaxies. They record this data on a spectrogram to learn more about the chemicals that make up the stars. However, some types of outdoor lighting, such as mercury vapor lamps, emit light that also gets recorded on the spectrogram, making the data very hard to read.
Other Negative Effects
- Poorly designed lighting that allows energy to escape upward where it's not needed is a waste of resources. Street lighting is more expensive than it should be and wastes a lot of electricity. In addition, light pollution harms nocturnal animals, cutting down on their habitat areas. According to the American Association for Cancer Research, new work being done into the effects of night lighting on humans suggests that a lack of darkness affects peoples' hormone balance, leading to problems as diverse as weight gain and breast cancer.
Solutions
- Several worldwide campaigns call on both homeowners and municipal authorities to replace inefficient and poorly designed outdoor lighting with "dark sky approved" fixtures. These fixtures direct all of their light downward onto the streetscape so that sky glow is drastically cut.

Astronomy