Lately, I’ve been thinking about when I first became aware of light pollution—or, more specifically, why I can’t recall hearing much about it on TV, radio, or through other media as I was growing up. I do remember the occasional documentary, like those showing baby turtles hatching on distant beaches. I’m sure you know the ones I’m talking about. The narrator would describe how artificial lights from nearby resorts could confuse the hatchlings, drawing them away from the ocean’s natural light—which they instinctively follow—toward the dangers of a busy beachside town. The imagery of the baby turtles really stuck with me back then (maybe it did for you, too), but light pollution seemed like a very distant problem, one I had little control over. I’m not even convinced the term “light pollution” was used; if it was, the messaging wasn’t strong enough to make it feel like a pressing issue.
So, before 2020, it’s fair to say that I hadn’t thought much about light pollution at all. Like many others, except perhaps astronomers or conservationists, I was more exposed—through media adverts, articles, and nature programs—to other, more commonly discussed terms and problems, like global warming, climate change, or, more recently, biodiversity loss.
However, nowadays, it feels like hardly a day goes by without these issues being front and center in news articles. At times, I have to admit, it feels like a very bleak picture is being painted for the future. It’s easy to feel helpless. I sometimes wonder if raising the profile of less familiar environmental terms (like light pollution) might add to the sense of apathy, disengagement, or anxiety people may feel about the global environmental crisis.
But there is cause for hope, and actions are being taken to mitigate the impact of human activities on the environment, particularly with regard to light pollution. In fact, a growing number of incredible dark sky advocates from around the world are working to make a difference.
In this post, I’ll be discussing what light pollution is, the impact it can have on all living things, how it is being measured, and what is being done about it. I’ll also talk about how everyone, including you and me, can take action through simple adjustments in the way we use light. With many things in life, it’s always about striking the right balance, and I hope that’s the message you take from reading this today.
What is Light Pollution and why has it become a problem?
Before I answer this question, it is important to note that not all light is harmful, and, of course, we do need it for essential day-to-day activities. The problem often lies more in how lighting is used rather than the fact that it is used at all.
Population growth over the coming decades is expected to be one of the most significant drivers of habitat and biodiversity loss (IPBES, 2019; Fenoglio et al., 2021; Simkin et al., 2022; Theodorou, 2022) and is closely linked to factors such as urbanisation and urban expansion. As urban areas grow, natural habitats are lost and replaced by human infrastructure—streets and residential areas, outdoor spaces, and facilities, including retail, industrial, transportation, and illuminated signs. Consequently, these developments lead to a corresponding increase in the demand for lighting and an upsurge in Artificial Light At Night (ALAN).
Light pollution occurs when ALAN is used inappropriately or excessively (Cupertino et al., 2023) or when light emissions are misdirected (Kocifaj, Wallner, & Barentine, 2023). Some sources of ALAN include:
- Glare—from overly bright lighting;
- Clutter—from excessively used and densely packed lighting;
- Light trespass—caused by the intrusion of light into adjacent properties (such as when a nearby streetlight casts light into your home, even with curtains or blinds);
and perhaps most notably,
- Skyglow—the upward scattering of light that brightens the night sky above populated areas. You may have seen this if you have ever looked from a darker place towards a larger town or city. A dome of light will be clearly visible and allows you to instantly identify the magnitude of the problem.
Recent research suggests that around 80% of the world is now impacted by light pollution, and the night sky became brighter by 9.6% per year between 2011 and 2022 (Kyba et al., 2023). The challenge we face is how best to balance the benefits of ALAN against its potential negative consequences (Barentine, 2022).
Is it really all that bad?
In short, yes, light pollution can, in some cases, have a huge impact—although in many instances, it is completely preventable.
There is evidence that artificial light at night (ALAN) causes significant and detrimental effects on biodiversity, impacting migratory birds, bats, moths, glowworms, amphibians, trees, fungi, and plant life. ALAN also affects human physical health as well as mental health too (Barnes & Passmore, 2024; Burns et al., 2023).
Additionally, ALAN leads to substantial energy loss when used needlessly or inefficiently (Meier et al., 2015; Falchi et al., 2019), accounting for around 20% of global electricity consumption (Challéat et al., 2021). It may also contribute significantly to carbon dioxide emissions and global climate change (Gaston & Sánchez, 2022). The degradation of natural dark skies due to ALAN is likely to impact our cultural and historical heritage as well (Dalgleish & Bjelajac, 2022; Falchi et al., 2023).
Needless to say, light pollution poses a substantial threat to our natural environment and may represent one of the most significant yet under-reported contributors to the ongoing environmental crisis.
In the video below BettyMaya Foott (a Dark Sky Advocate) provides more detail about the impact of light pollution in her TEDx talk. It is definitely worth watching if you have time!
How is light pollution measured?
Light pollution is measured using several methods to help us understand its impact on the night sky. One common approach involves handheld devices called Sky Quality Meters (SQMs), which measure how bright the night sky is at a specific location. Lower readings indicate higher light pollution. All-sky photometers are another tool that takes wide-angle images of the entire sky, providing detailed maps of light brightness over large areas.
Satellites also play a crucial role in monitoring light pollution. The VIIRS (Visible Infrared Imaging Radiometer Suite) sensor on the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite measures the brightness of artificial light from the Earth’s surface at night. This data helps track light pollution patterns globally and observe changes over time.
In addition to these tools, the Bortle Dark-Sky Scale is used to qualitatively assess the darkness of the night sky based on visual observations. The scale ranges from 1, indicating pristine dark skies, to 9, representing the brightest urban skies. It helps astronomers and stargazers gauge the level of light pollution and its impact on their ability to see celestial objects.
There are citizen science projects too, like “Globe at Night“, that invite volunteers (anyone!) to report how many stars they can see (with their eyes), contributing valuable data on sky brightness. As you might be able to tell from the image above, the brighter the environment is the more this whitewashes the sky, reducing the number of stars we see. In many cities and towns across the world its likely that only a handful of stars will be visible, but in the places where it is naturally the darkest, there can be anywhere between 2,500 to 5,000 stars visible. I often wonder what it must have been like for people living before the invention of the light bulb. Everyone before this time would have been able to experience true natural darkness and the main source of light at night would have been the moon and stars. Sadly, many of us, will never know what that is like or visit some of the darker places and experience the wonders of the night.
Nevertheless, these methods provide a comprehensive view of light pollution, aiding communities and policymakers in taking steps to mitigate its effects on wildlife, human health, and our enjoyment of the natural night sky.
Want to know how light-polluted it is where you live? If you go to Light Pollution Map and enter your postcode/zipcode you can see the extent of light pollution in your local area.
How can I help and what else is being done to fix this problem?
Without a doubt, you should check out the Dark Sky Association’s webpages here – https://darksky.org/ – as everyone, no matter where they are in the world, can make a difference.
Below, I will explain who the Dark Sky Association are and outline the various ways you can help protect natural darkness.
The Dark Sky Association is a nonprofit organization dedicated to protecting our night skies from light pollution. Established in 1988, the association works to reduce the negative impacts of artificial light by promoting better lighting practices. Their goal is to make outdoor lighting more efficient and less disruptive to the natural night environment.
The association also educates the public about the importance of preserving dark skies through various resources and events. They have programs to recognise and certify places like parks and communities that make significant efforts to reduce light pollution. By supporting research, collaborating with experts, and engaging with local communities, The Dark Sky Association helps to maintain the beauty of the night sky, protect wildlife, and improve our overall quality of life.
But if you want to know how you can make a difference simply and easily, often at no cost, then you should check out their Five Principles of Outdoor Lighting and their Guides and how-tos section on their webpage.
Some closing reflections
I hope that you have found this information helpful about the complexities of light pollution and its far-reaching effects. By understanding how light pollution is measured and recognising its impact on both the environment and human health, we can better appreciate the importance of addressing this issue. The Dark Sky Association offer a useful path forward, demonstrating that positive change is possible through informed action. I encourage you to explore these resources and consider how you might contribute to preserving the beauty of the night sky. Every small action counts, and together, we can make a significant difference.
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