Artificial light brightening the night sky around coastal cities causes light pollution that reaches a whopping 75% of the nearby seafloor.

You’re Glowing

With global population increases and subsequent city expansions, it makes sense that the glow cast from city light to the night sky is growing steadily. In today’s societies, more people are moving to the coast to settle in beachside regions. Coastal populations are on trend to double in size by the year 2060. Although living right on the doorstep of the ocean sounds wonderful and harmless, with the sheer number of people thinking the same thing, the reality is that our presence on the shore harms underwater environments.

With more people living along the shoreline, there are increased greenhouse gas and toxic chemical emissions. Further, our presence means that niche coastal habitats are disturbed, causing displacement and even extinction of some endemic species. But one of the biggest disruptions our presence there causes—as well as one of the most underestimated—is the amount of light we emit at night.


The term “skyglow” has been given to the effect our major cities and skyscrapers have on the evening sky with their ever-glowing light sources. Even though its presence is so obvious to the naked eye when looking up, the effects of it go by nearly undetected. A recent study born from a team of UK scientists was conducted in a busy Western Europe port that created artificial light sources on evenings when there was little to no moonlight to mimic the city’s skyglow. Even though it has been suspected for some time that such unnatural light sources can cause light pollution with potentially harmful effects on surrounding environments, it was not until this skyglow study that they have been quantifiably demonstrated and measured.

“We could see the light from the city being reflected across all the clouds all the way up…”

Moving ~3 km away from the illuminated city, the scientists used a combination of novel techniques and methods including mapping and radiative transfer modeling tools to measure light exposure both at and beneath the surface as well as the seafloor. Their results were staggering: between 70% and 76% of the seafloor space surrounding coastal cities was exposed to light pollution from city skyglow. Originally, they assumed that their hypothesis of city light being able to reach the seafloor was a bit ludicrous, but were proved wrong by the power of sheer reflection off of the night sky. One of the lead researchers, Dr. Thomas Davies, was quoted saying: “We could see the light from the city being reflected across all the clouds all the way up, right above us, right over [the] top of us and off into the distance…”, an extremely humbling moment to both him and his team.

Another worrisome finding was that a main factor behind the high exposure levels is the use of LED lights. With cities pushing to be more sustainable and serve as green spaces over recent years, many buildings and local infrastructure installments have switched to LEDs. Even though this switch is great in terms of energy usage, it has a trade-off cost with resultant light pollution in surrounding marine habitats. Because water acts as a filter, the surface and water column can only be penetrated by certain types of color waves. Blue and green wavelengths are the most suited to the shallow waters of the coastline; of which LEDs create in abundance.

After(glow) Effects

Constant light sources are not generally seen as a good thing. Think of how disrupted your sleep patterns get when you change time zones: how much would your lifestyle be altered if you had constant light around you with no curtains to shut it out? Now think about if you were vision impaired, and relied on subtle changes in light and shadows to carry out your life-cycle processes. Strangely—or not, depending on how you see it—we are not that different from animals in that artificial light can harm both human health as well as marine ecosystem health. Excess light from ships has even been recorded to disturb certain fish species and raise stress levels in coral reef systems.

Many marine creatures are heavily-reliant on lunar patterns for their life cycles, including timing for feeding. Some species use moonlight direction for navigation while others follow lunar patterns for reproduction cycles. Therefore, discovering that around three-quarters of the entire seabed in the study area was bathed in artificial light was shocking. Such a large amount could realistically devastate an ecosystem, rather than slightly harm it as was originally thought. Other potential issues for concern with coastal species are the loss of carefully-cultured night-time camouflage mechanisms that ultimately render useless under permanent light situations. If marine flora and fauna become too stressed from constantly-lit habitats, their ecosystems could be critically damaged. Because this finding is relatively new, the exact way that coastal species are influenced is not known. Further research and efforts are very much needed to determine how we can mitigate our damage.

Shedding Light on the Way Forward

The enormous uncertainty in this particular field of light pollution is the most pressing concern for right now. Resounding concern based on the results of the skyglow study is garnering positive feedback and necessary attention among today’s scientists, so there is hope that enough backing will be allocated to it in the near future. As is the case with anthropogenic influence and us waking up to just how much we affect our immediate and deep-seated environment around us, we do need to act fast. Long-term impacts could be devastating and irreversible for many endemic species of niche aquatic habitats. Hence, the sooner efforts are carried out to assist them with mitigating and/or adapting to our forced changes, the better. Head over to this page to see more details on the groundbreaking skyglow study and the researchers who designed it.

Many scientists who were not involved in this particular study have now weighed in, adding their voice to the platform, and designing their own projects to complement and add to this work. The easiest way for you and I to make a difference right now is to ask ourselves these four basic questions when deciding to use artificial light or not, put forward by Davies, the lead researcher on the skyglow study.

  1. Do I need it?
  2. How much of it do I need?
  3. When do I need it?
  4. What color can it be?

Even by simply going through the motions of asking ourselves these questions, we open up the discussion. Maybe the discussion is one-sided and just with ourselves for right now, but it most definitely will gain traction once our trends become visible.