Light Pollution – It’s Not Just Astrophotographers Who Hate It

10 minute read time

We’ve all heard the term “light pollution” at some point. But what is it, how do we measure it, and how can we cut down on it? Up until recently I’ve merely accepted light pollution as something (else) I have to deal with. But I was approached by a researcher asking to use my image of the Milky Way rising over the Thrupp and Brimscombe Valley in a paper they were doing to support an attempt to get areas of the Cotswolds AONB declared as a dark sky reserve. I’m lucky living in the Five Valleys around Stroud and Nailsworth, as the skies here are pretty decent, but this piqued my interest further about what constitutes light pollution, and I was actually horrified by some of the findings.

For us astrophotographers light pollution can be the bain of our lives. It’s hard enough dealing with clouds, wind, rain, equipment failures and a myriad other things that curtail our already limited time under the night sky. We also have to deal with streetlights, flood lights, headlights, and not to mention, at completely random intervals, the kitchen lights! The more recent onset of LED lighting has only exacerbated the issue as well. Blue LED lights can now be found everywhere; in the phone you’re probably holding, in home lighting, street lighting, car headlights to name but a few. And whilst these are used for their (relatively) lower energy usage and comparative cost effectiveness, they’re actually pretty harmful.

Yes, there’s ways of working around it, all of which are less than ideal, both during the image acquisition itself, with such things as light pollution and narrowband filters that block out large swathes of the bandwidths that those lights operate in, and also during the post processing stage when we’re trying our best to pull out those tantalising hidden details without increasing the effects of the light pollution as well.

But decent filters are expensive, and the rabbit hole of astrophotography already costs both kidneys, our liver and probably a limb or two as well. They’re also no substitute for getting out and into some dark skies.

These are a large part of the reasons you’ll find us astrophotographers and amateur astronomers seeking out places far away from cities and towns. But this assumes we have the means of transportation AND the time to get ourselves wherever we’re going. Then there’s the cost of fuel, carbon footprint, having to buy additional equipment to enable us to go portable out in the field. It all adds up.

In fairness I personally enjoy being under a decent dark sky away from everything. It’s calming and soothing to my nerves. At least until you hear a fox nearby. For anyone who’s never heard a fox in the dead of night, it’s akin to someone being murdered. At 2am, in a field miles from anyone and anywhere to say that it can be somewhat disconcerting would be a bit of an understatement. It’s like doing a 4th to 1st instead of 4th to 3rd gear change at 50mph unexpectedly. Kind of throws you off your stride a bit. Anyone who’s read Douglas Adams will know what I mean. But to get back to the light pollution issue…

What IS Light Pollution?

Essentially, light pollution is the inappropriate and excessive use of artificial light, and it comes under four main types:

Glare – blinding and causes visual discomfort.
Sky glow – brightening of the night sky over inhabited areas.
Light trespass – light falling where it is not intended or needed
Light clutter – bright, confusing and excessive grouping of light sources

Measuring Light Pollution

Being able to measure the amount of LP at a given location used to be something that was reserved for those with understanding of advanced mathematics (ie algebra) and those with specific equipment such as SQM (sky quality meter.) These days, thanks to advances in mobile phone camera technology, pretty much anyone can do it with a smartphone using the apps Loss of Night (free on Android and iOS) or Dark Sky Meter for iOS at £1.99. You can also use the app Clear Outside produced by First Light Optics, which will take your phone’s GPS position to give you an estimated sky class for your real time position.

As an astronomer we often use a system known as the Bortle scale. This is a scale that ranges from 1-9, with 1 being the best and 9 being the worse. Typically I image in either a class 4 at my home in Nailsworth, or class 5 at my children’s in Gloucester. Whilst this may not sound like much difference, it can be the difference between using a CLS (city light suppression) filter or not. And although these can be effective in blocking a lot of the city light, their effects mean that we often don’t capture the more natural star colours, something we need to address in post processing.

The differences in Bortle class. Image from Astrobackyard

The Effects of Light Pollution

Light pollution (or LP) does a lot more than hide our view of the stars that our ancestors both worshipped and studied. Being able to connect with the night sky has been an important part of both our ancient history and heritage, leading to quite profound realisations about our place in the cosmos. Without that ability to connect and study them, we might possibly still be under the misplaced perception that the Earth is the centre of everything. Of course we now know that to not be the case, but that’s only through our efforts and ability to study the night sky.

Not just that, our ancestors used the stars to gauge essential periods throughout the year, such as when to plant crops, when to harvest, when winter was coming, to name but a few. Farmers and some indigenous tribes still do this, but the encroachment of LP throughout the environment, and the proliferation of sky glow is making this more difficult as time goes on.

And LP has other effects that are much more immediately harmful, not just to homo sapiens, but other life on our planet as well. An article by National Geographic provides a quite vivid picture of the effects of LP on the environment.

When it comes to wildlife, LP has been observed to affect such things as migration patterns, habitat formation, wake-sleep habits etc. Guided by moonlight, sea turtles and some birds often become confused by light pollution, lose their way and then die. Insects, often a primary food source for birds and other animals, are attracted to our bright artificial lights, often being killed instantly.

In summary, LP is a GLOBAL issue. More than 80% of the world’s population, and 99% of Americans and Europeans live under the effects of sky glow. Artificial light can wreak havoc on the natural body rhythms of humans and other animals, interrupting sleep and upsetting circadian rhythms in nearly all organic life. It also has the effect of reducing melatonin, a natural hormone that’s produced when it’s dark and tells us it’s time to sleep. In fact a recent study has also linked reduced melatonin production with cancer. And that’s on top of the sleep deprivation, fatigue, headaches, stress, anxiety and a myriad of other health problems.

But all that light at night makes things safer…doesn’t it?

In actual fact there is a growing body of evidence that supports exactly the opposite! It might make us FEEL safer, but a 2015 study found that streetlights had negligible impact on accidents and crime, but DO cost a lot of money.

According to a 2012 report by the AMA “glare from nighttime lighting can create hazards ranging from visual discomfort to frank visual disability.”

These are only two studies as quoted by the International Dark Sky Association (IDA.) A quick online search will yield many more results. But the bottom line is that there is a growing body of evidence to support the idea that increased lighting at night is having exactly the opposite effects of the reasons given for it by many local authorities. The truth of the matter is that bad outdoor lighting in actual fact DECREASES safety by making victims and property easier to see. In fact the majority of crime occurs in broad daylight.

Outdoor lighting is supposed to enhance safety and security at night, but too much lighting actually has the opposite effect. Directed, aimed lighting where it is needed creates a balance between safety and starlight. The glare from bright and unshielded light decreases safety because it shines directly in our eyes and causes our pupils to constrict, blinding us and making it more difficult to adjust to low light situations.

The fact remains that street lighting both costs a great deal, and is very energy inefficient, in a day and age where our focus is, rightly, increasingly on the environment and our effects within it. That we CHOOSE to not address our environmental impact is non-sensical. An oddity my partner Amanda has observed is our almost unconscious distancing of ourselves from what we refer to as “the environment”, almost as if we’re not a part of it. In fact I myself have done the very same on occasion. WE are a part of the same environment that we affect.

Each and every species of plant and animal life on our planet is interlinked and interdependent in some way. And yet we just shrug our shoulders. We as a species have a huge effect on the world around us, with more and more species going into extinction year on year. And yet we have the ability to mitigate that. What we lack is the will to do so. I’ve taken the liberty of contacting my local county council on the subject, but if local authorities run true to form, I’m not expecting much beyond a generalised response.

As you can see it’s not just us astrophotographers and amateur astronomers who suffer with light pollution, it’s ALL OF US.

Thank you for reading, and clear skies all…assuming no light pollution


International Dark Sky Association

National Geographic Society


Loss of the Night Citizen Science Project


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