Streetlights not the main cause of light pollution

Streetlights only responsible for 20% of light pollution. Source: unsplash (via Pxhere)
New study shows streetlights only responisble for 20% of light pollution, meaning more needs to be done by policy makers.

By Holly Giles | Deputy Editor 

The sight of a truly dark sky filled with stars is something that up to 80% of the population are no longer able to see due to light pollution. Light pollution is largest in cities where it “lights up the sky” so stars can no longer be seen. 

Many climate activists have blamed streetlights as a major cause of light pollution in cities. To test this, a team of researchers from Germany, the USA and Ireland teamed up with the american city of Tucson to look at the true effect of streetlights.

Tucson has 14,000 street lights which have a bright and dim setting. The dim setting is normally switched on at midnight to emit 60% of the normal light in a bid to reduce the city’s pollution. For the experiment the streetlights were kept at 100% for 5 nights and then reduced to 30% for the further 5 nights. By comparing the cloud images it was possible to see how much light was caused by street lights.

The team found only 20% of the light in satellite images comes from streetlights. This result is important with regards to sustainability and means policy makers need to do more than just police streetlight use. Co-author of the study, Dr John Barentine, explained: “these studies show that in a city with well-designed streetlights, most of the light emissions and light pollution come from other lights”. Barentine gave examples of bright shop windows, lit advertising signs, car parks and sports fields as other contributors to light pollution that are often overlooked. 

Reflecting on these multiple sources of light pollution, lead researcher Dr Christopher Kyba, told:

“This does make it more difficult to solve, because there are so many contributors. It means everyone has to get together to decide what lights need to be lit at night, and how brightly”.

Speaking specifically about the Tucson smart streetlights, Kyba continued:

“Instead of dimming lights to the same level each night, a city could instead dim to 45% on even days and 55% on odd days. City residents wouldn’t notice any difference, but that way we could measure how the contribution of different light types is changing over time”. 

This wasted light is not only important for our climate but also equates to about $3 billion per year being spent on nighttime lighting. This is doubly important as while that money could be used elsewhere, the electricity could be put to more beneficial use, for example to charge electric vehicles to reduce the need for fossil fuels in the day. As Dr Kyba explained

“It’s the kind of thing that can be done with a little bit of cleverness and the will to take action”.

It is hoped this research will show policy makers that rules on streetlights are not enough to counter light pollution given off in some of the world’s major cities. By cutting our light pollution we can save money and protect our world.


Science and Technology Holly Giles

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