What Is Light Pollution and Why Is It an Issue?

Updated on November 5, 2018
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Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.


I am sure most of us are already painfully aware of the lack of stars in our night sky. Sure, you may see plenty of them now but not as many as you would if away from the urban life and out in the countryside. And the fact that most Americans have never seen the Milky Way, something that humans have witnessed for millennia, is profoundly sad for the simple reason of its intrinsic beauty. Many factors have contributed to these missing nighttime features from our skies but none is as troublesome as light pollution. While much can be done to combat it, educating people about proactive steps in solving this is challenging. The best place to start is to go over why it is a problem and from there address adequate and feasible means of action.

The Rise of Light

As the rise of the cities spread across the world after World War II, light was needed as productivity and luxury grew. Rather than put in a ton of incandescent bulbs and replace them frequently, mercury vapor lights were used starting in the 1960’s as a cheaper but less efficient method of providing illumination. Eventually, sodium vapor replaced mercury vapor. Those orange lights you see on the street lampposts are sodium vapor-based and are 50% more efficient than mercury. That is, they require half as much electricity to provide the same brightness, thus saving energy and therefore money. And, as we shall soon see, they are better for astronomers (43).

Comparing the clear vs. polluted sky.
Comparing the clear vs. polluted sky. | Source

Action Begins

While it is true that outdoor lighting has its purposes, it is sad to say that up to 40% of street light is wasted by being projected upward because of design flaws. Not only is it a waste of energy but also money that we the people pay as taxes. And the amount of damage it causes the astronomical community is devastating. It makes ground-based a.k.a. affordable astronomy less and less achievable. So why hasn’t more been done about this? For one, a lack of attention has plagued light pollution activists. They simply cannot compete with other major news and interests groups, especially when the solution is not easy and requires a change in lifestyle. They know, however, that if people in charge are made to care about it (especially when a savings in a budget is possible) then something will be done. At any rate, change has to start somewhere (42, 44).

In 1972 Tuscon, Arizona became the first documented town to try to do something about the light pollution it faced. After all, Kitt Peak Observatory is located there and if too much pollution enters the sky then they are done as far as being a useful tool to astronomy. The town made streetlight panels to direct the light downward mandatory, thanks to the efforts of engineers who worked with the local astronomers (42).

In 1972, Merle Walker of the Lick Observatory in California conducted an investigation into light pollution. Ironically, the location of Lick was chosen because of light pollution considerations. It was initially to be located at Mt. Wilson but in the 1930’s the growth of cities caused Mt. Palomar to be a more attractive option because of how remote it was. However, the simple nature of population and industrial growth caused Walker to look into light pollution and spread public awareness. Sandra Faher joined Walker in 1979. Also an astronomer at Lick, she too felt that light pollution was going to be a real issue soon. But she had a simple solution: change the lights (43).

LED light in foreground with an HPS light in the background.
LED light in foreground with an HPS light in the background. | Source


Believe it or not but sodium vapor lights come in two flavors: high pressure (HPS) and low pressure (LPS). Both of these have different signatures in an electromagnetic spectrum and thus are important to distinguish. HPS are more in the red portion of the spectrum than LPS (making dimmer objects difficult to see) and are harder to filter out while LPS have a narrow wavelength and thus make them easier to remove. Anything that is easily removed from the spectrum to maintain data is desired, so it seems like LPS is the best choice, right? (44)

Some studies seem to go back and forth between the two for technical and sometimes incorrect reasons but most agree that LPS is less harmful than mercury. Faher pointed out that HPS would cause an increase of noise in the red band of the spectrum by 35% compared to mercury. She did find that LPS’s 2 emission lines would be an improvement over mercury’s 6, making it easier to remove from data (44).

Shedding More Light

Faher was very detailed in her findings and discovered some more interesting facts. 35% of the light pollution at the time of her study was caused solely by streetlights and not buildings, and having downward shields to direct the streetlight did not help Lick Observatory, though it is unclear why. She did feel that LPS was the best choice for streetlight based on prior work but for her viewpoint it was primarily because of the minimal spectrum interference (44).

Shielded vs. non-shielded.
Shielded vs. non-shielded. | Source

1978 saw San Jose publish a report on Sodium Vapor Luminaire Conversion. It detailed many interesting facets of the potential conversion, one of which was how LPS was 20% cheaper to install than HPS. Over the lifetime of a LPS light, the maintenance as well as operating costs was less than HPS. Also, after 9 years of use, the savings of LPS from HPS add up to the initial costs of installing the LPS in the first place versus the installation of the HPS. The conversion would save San Jose about $1 million (or over $3.5 million, once inflation is taken into account) and would not degrade the quality of light the city had (45).

The Stand Today

The light on HPS vs. LPS was eventually settled with LPS being generally accepted today. Sadly, light pollution continues to be a problem to this day. Studies have shown how light which is directed above the horizon (i.e. wasted) amounts to between $1 and $2 billion lost a year in the US due to electric costs. And yes, how much above the horizon it leaves impacts astronomers even more. This is because a light ray which goes straight up enters space fast and covers less sky but a light ray more in line with the horizon passes through more sky and obstructs more data. On top of that, the reduced angle allows the light to be 90% absorbed by the air as opposed to the 20-30%, which occurs when the light goes straight up. And surprisingly, local light impacts observatories more than major cities which are a few miles away (Upgren).

Old vs. new.
Old vs. new. | Source

And the battle grows more complicated. As it turns out, the rise of LEDs has added a new wrinkle: their cheapness, efficiency (white LEDs can last 100 times as long as incandescent bulbs and 10 times as long as fluorescent bulbs), and low maintenance has made them commonplace but their output blocks lots of light astronomers are interested in. And the best part? The push for LED was initially in response to the HPS/LPS debacle, but blue LED light kills off the 450 nano-meter portion of the spectrum, something CCD cameras utilize. Some places are trying to make LEDs more green/red based while others are trying to add a filter to take out more blue light. Another attempt at resolving this is utilizing lower-temperature LEDs, which are less blue in color (Betz, Skibba).

But all is not lost. San Francisco installed many lamp hoods that direct the lights down and now saves about $3 million a year. The cutoffs also improve nighttime viewing conditions, meaning that motorists are safer and thus another reason to justify the covers for the non-astronomers out there. Many highways in California reduced the lighting along the highways and increased the use of reflectors, further diminishing the light pollution. And in 1988 the International Dark Sky Association (IDA) was formed by David Crawford (Kitt Peak Observatory) and Tim Hunter. Over the years they have found sites across the nation that allow for great nighttime viewing conditions and have also created new ones. The IDA continues the fight for better light – control, that is (Upgren, Owen).

Works Cited

Betz, Eric. "A New Fight for the Night." Discover Nov. 2015: 59-60. Print.

Brunk, Berry. “Bright Lights Ahead.” Astronomy Apr. 1982: 42-5. Print.

Owen, David. “The Dark Side.” NewYorker.com. The New Yorker, 20 Aug. 2007. Web. 15 Sept. 2015.

Skibba, Ramin. "Astronomers Encourage Cities to Shield Outdoor Lighting." insidescience.com. AIP, 30 Jan. 2017. Web. 05 Nov. 2018.

Upgren, Arthur R. “Everything You Ever Wanted to Know About Light Pollution.” SkyandTelescope.com. F+W Media, 17 Jul. 2006. Web. 14 Sept. 2015.

© 2016 Leonard Kelley


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