Light pollution

Have you watched our night sky the last couple of years and noticed the change in the amount of stars? Yes you are right, the stars are disappearing. For three billion years, life on Earth existed in a rhythm of light and dark that was created exclusively by illumination of the sun, moon and stars. But the entire conversion of the night-time environment started nearly as soon Thomas Edison developed his first lightbulb.

Nowadays, artificial lights overpower the darkness and our cities glow at night, interrupting the natural day—night pattern and shifting the delicate balance of our environment. Less than 100 years ago, everyone could look up and see a spectacular starry night sky. Now, we are even happy if we can see a couple of stars. But what is the cause of the vanishing of the night sky as we used to know? Light pollution, also known as Skyglow, is the answer. This is one of the numerous ways that our Planet is artificial polluted, but additionally one of the ways that we don’t realize as much.

“Twinkle, twinkle, little star,

How I wonder where you are.

Looking up is no solution;

The sky's so full of light pollution.”

— David H. Levy

Light pollution is the over-illumination of cities and night skies by artificial lighting. Several types of light pollution exist, including glare, which is a disruptive light that shines horizontally. Light trespass, the unwanted shining of light onto nearby areas. And skyglow, a halo over inhabited areas caused by the scattering of light in the atmosphere by water, dust, and gas molecules that appears over cities at night an keeps citizens from seeing stars (Gaston et al., 2017).

A study published by Falchi et al., (2016) documenting light pollution across the globe showed that more than 80% of the worlds population is living under light polluted skies. Europe and The United States have the highest percentage, with 99% of the residents experiencing skyglow at night.

In 1800, only two percent of the worlds population lived in cities. In 1950, this percentage had risen to thirty percent and in 2007 more than half of the global population lived in cities. Today, there is a discernible acceleration of this urbanisation, with the number of city dwellers growing by a half million each week. This means that in 2030, sixty percent of the world population will live in urban regions. 

This accelerated growth of urban populations imposes higher requirements on the infrastructure around and in cities such as artificial light. 

Light pollution impacts health of humans and animals, especially nocturnal wildlife, and disrupts ecosystems. But first we have to know, what is light exactly and why do we need light, before we are able to dive into the more detailed impacts of light. 

Light can be contained in a few ways. Before the electrical age, light consisted of fire. Oil and wax were primarily used as a light source. When Thomas Edison invented the light bulb through electricity, the possibilities of using light became limitless. From this point forward, light usage only intensified, as more ways of using electrical light were discovered.

We have lit up streets, parking lots, buildings and every populated space we can mostly to make the night “more save”. However, no study has ever shown that more light leads to less crime. A research conducted by Steinbach et al., (2015) over the effect of reduced street lighting on road casualties and crime in England and Wales. They found little evidence that streetlights prevent accidents or crime. The researchers examined at the information on road traffic accidents and criminality in 62 local authorities in England and Wales and found that lighting had no effect. No matter whether authorities had turned them off entirely, dimmed them, turned them off at certain hours, or replaced by low-power LED lamps.

Quite the opposite, bad outdoor lighting causes glare which can decrease safety. Morrow et al., (2000) showed a correlation between brightly lit alleys and increased crime. And according to Blask & Brainard (2012) can glare from light-time lighting create hazards ranging from discomfort to frank visual disability.

So brighter at night does not mean that it is safer. Outdoor lighting is meant to enhance safety and security during the night, but too much lighting can actually have the opposite effect.

Physiological responses to artificial light exposure result not just in the health the conditions specified above, but then also in large‐scale ecological changes (Navara & Nelson, 2007). For a long period, humans and other creatures evolved with their circadian rhythms of night and day. Changes in the natural light rhythm evoke a multitude of physiological and behavioural changes within animals (Van’t Hof & Stokkan, 1999).  

Though, timing can be everything in biology. Whether it is gene expression, metabolic or physiological processes, organismal activities, resource acquisition, or reproduction, getting the timing right can often be crucial to fitness and survival. Natural light cycles are the most powerful and predictable environment fluctuations that organisms typically experience (Gaston et al., 2014).

They have thus also become the most important environmental cues for biological timings. These include daily events (e.g., enzyme activity, photosynthetic activity, flower opening, singing, foraging, movements, sleep and recovery), which are often regulated by circadian rhythms, and seasonal events (e.g., growth, hibernation, molt, reproduction and migration), which often use change in daylength or photoperiod. (Gaston et al., 2017)

In many cases, anthropogenic influences on the natural rhythms result from changes to the environmental cues that organisms use for determining the timing of events. Thus, the influence of direct interference of artificial lighting along with natural light cycles is of fundamental importance to comprehending the biological effects of anthropogenic pressures. (Gaston et al., 2017)

Biological impacts on artificial night-time lighting have long been documented, the last decade has also seen an explosion of examples of the profound effects on health and well-being of organisms from field studies. (Gaston et al., 2013). 

These impacts have been especially recognized through direct measurement in the field (e.g., Kempenaers et al., 2010, Davies et al., 2012), through experimental introduction of street lights into formerly darkened sites (e.g., Hölker et al. 2015, Spoelstra et al., 2015), as well as by imitating of street lights emissions during other experiments (e.g., Bennie et al., 2015, Sanders et al., 2015). Impacts have been found on a wide diversity of organisms, including microbes, plants, mollusks, insects, fish, amphibians, reptiles, birds, and mammals (Gaston et al., 2013).

One “case” stood out. 

Phototaxis, as described by Bendix in 1960, is the movement of an organism in response to a light stimulus. Phototaxis can be positive and negative. A negative phototaxis means an animal is attracted to the dark, or a lack of light. A positive phototaxis is when an animal is attracted to a light source (Bendix, 1960). This is what happens when the lights shine into the sky on September 11th in Manhattan. Birds are positively phototactic and thus attracted to the giant lights in the sky. 

It has long been known that migrating birds can somehow visually perceive the magnetic field of the Earth to help them navigate during migration. Two researches recently found evidence of how birds can see the magnetic field. A Swedish research by Pinzon-Rodriguez et al (2018) found that the cryptochrome 4 protein (CRY4) in the eyes of zebra finches is the key to how birds can see the magnetic field. A German research by Günther et al (2018) showed the same result in robins earlier in 2018. The CRY4 protein is especially sensitive to blue light. It was found that the production of this CRY4 protein is significantly higher in migratory birds during the migration season than during non-migratory seasons (Günther, 2018). 

Most migrating birds migrate at night, using visual cues and magnetic orientation to help them go in the right direction (Maclaren, 2018). Birds are thought to have specialised receptors in their eyes capable of picking up certain wavelengths of light that will guide them through the darkness. This happens through the aforementioned proteins in the eye (Günther, 2018). When artificial light comes into play, shining their often white-yellow light into the dark, these blue-green wavelengths are distorted. These distorted wavelengths disorient the birds and causes them to rely fully on visual cues.

The problem is, the lights are often so bright that they massively attract these birds, which causes collisions with structures (van Doren, 2017).

Artificial light at night also influences habitat selection in migrating birds. When looking for a stop, migrating birds are more likely to rest in a well-lit area than in a dark area (Maclaren, 2018). This has implications for the fitness of the birds, as the most well-lit areas aren’t necessarily the most suitable for the birds (Maclaren, 2018). Often there’s little food availability, which is crucial to a good proceeding of migration. If the birds don’t eat as well as they should, many won’t survive the journey at all (Maclaren 2018).

A research by Poot et al in 2008 offered a possible solution to the problems that arise with artificial light at night. As mostly blue light is used by birds to navigate the magnetic field of the Earth, white and yellow lights can be changed to green lights. The difference in frequency of the electromagnetic waves are less disturbing for the birds, who will not get disoriented then. It sounds like the perfect solution, but the research also stated that it is so yet to be researched what the impact of the change of light could mean for other nocturnal animals like bats.

Spoelstra et al concluded in 2017 that white and green light should be avoided in areas with bats. The results of this research show a significant decrease of activity of the bat species myotis and plycotus when green lights are used, while there is no decrease of activity when red lights are used. Thus, the conclusion was: don’t use green or white lights but use red lights instead.

This conclusion conflicts with the advice for light colour for migratory birds, making it an interesting topic for research in the coming years.

As the story told before about the “Tribute in light” at 9/11 whereby pollution does not mean getting rid of all artificial light. The story was an example and inspiring way how humans and wildlife can co-exist in a world of artificial light. Projects as “Licht op Natuur” in The Netherlands and organisations as The International Dark Sky Association (IDSA) work with the public, city planners, legislators, lighting manufacturers, parks and protected areas to find and implement solutions.

There are five main groups of mitigation measures for the impacts of artificial nighttime lighting according to the IDSA and Gaston et al 2012:

• (a) maintaining and creating dark areas—identifying and protecting areas that remain dark and removing artificial lighting sources to create new ones;

• (b) reducing light trespass—improving the design and use of light sources so as to direct artificial light where it is actually required and to prevent it from being directed elsewhere;

• (c) dimming—reducing the intensity of artificial lighting emissions to optimize the balance between what is required for human activities and erosion of the natural nighttime environment;

• (d) part-night lighting—switching off lighting sources from late at night until the early hours of the morning (during which time they are often of little benefit to people); and

• (e) changing spectra—reducing the biological impacts of artificial nighttime lighting by using spectra that provide sufficient human benefit while minimizing other biological impacts (in particular, avoidance of emissions in the blue part of the spectrum is recommended owing to their stronger influence on circadian rhythms and on levels of skyglow).

Light pollution is not “all light at night” but it is “light out of place”. That is a message the IDSA wants to make especially clear.