Skyglow is the halo-like artificial illumination of the night sky above towns and cities. It’s also the name of a major new study into light pollution in the UK by Hillarys. Using satellite images taken between 1992 and 2014, Skyglow shows how the UK’s night-time skies have changed. The research charts a 28% decrease in light pollution*, with falls in every region – and projects this data into the future. You can see the interactive satellite imagery and full study on the Skyglow project page. Or keep reading to find out the story behind the story.
We knew what to expect with Skyglow. From the start, we expected to find that light pollution in the UK is rising.
Our expectations stood to reason. The population has grown 10% since 1992 and infrastructure must have developed to meet its needs, so light pollution should have increased too. Except – it hasn’t.
Skyglow discovered something way more interesting: night skies are darker across the country.
Why we chose to investigate Skyglow
Hillarys is a gold sponsor the International Year of Light and Light-based Technologies (IYL 2015). With our sponsorship, we wanted to look at how light affects our lives in both small and big ways, from our smartphones to photosynthesis to looking at the night sky.
The idea of investigating the night sky had our attention. We started to think about how our use of artificial lighting is causing light pollution and affecting the brightness of the night.
Day by day, our research uncovered more and more about the consequences light pollution has for our lives. We spoke to Dr. Bob Mizon MBE FRAS, who told us many people – and even well-equipped astronomers – struggle to see star-filled skies because of light pollution.
Our investigations turned to the energy issue. Despite some improvements in lighting design and efficiency, we found in the EU more than half the energy used for outdoor lighting is wasted.
Dr. John Barentine explained such careless lighting has an economic cost – and a cost to our quality of life. He said our biology and ecology are ill-equipped to handle night-time brightness in extreme measures and can suffer even in the presence of relatively small amounts of light. We found this kind of exposure to night-time light can disrupt our brainwave patterns, hormone production and cell regulation.
We decided to conduct our own research into light pollution.
What is the Skyglow project?
Skyglow came out of this initial research. We had pondered light pollution and whether it would have changed over the years. To us, at this point in the process, we were confident of finding a change and probably an increase.
Our ideas developed. Soon we were investigating ways of researching light pollution – one potential method stood out immediately.
Skyglow would take statistical data from night-time satellite images and chart historical trends in light pollution. Our method would allow us to put a value on how much artificial light escapes into the atmosphere nationwide and to break our findings down to a regional level.
In addition, we would look at the effects light pollution has on us and the wider environment. And we would use digital design to raise awareness of our findings and the issue online.
How we created Skyglow
With the help of Jurij Stare from Dark Skies Slovenia, we settled on using images from the Defence Meteorological Satellite Programme (DMSP). For each year, we created a single composite image from hundreds of satellite photographs, which allowed us to take account of day-to-day variations.
The DMSP records analogue images, so we converted these into a greyscale digital format. On each image, different shades of grey showed the varying intensity of artificial light escaping into the atmosphere – or the amount of light pollution being created.
So to create the data needed to compare light pollution over time, we awarded each shade of grey a value from 0 to 63 (0 being the darkest and 63 being the brightest). From here, we could work pixel by pixel and show light pollution increases and decreases as percentages.
The next step was to change the map from a WGS84 coordinate system (the kind used on Google Earth 3D) to a spherical Mercator (the standard map projection, found on Google Maps).
Last but not least, we applied a colour ramp, turning the greyscale images into a coloured and easy-to-understand format.
What Skyglow found
Our work shows that light pollution in the UK is down 28% since 1992*.
The findings took us by surprise. Sure, we knew that the way energy is consumed and lighting technology has changed over the years, but the UK population has grown over the same period. And it would make sense if the rising population had caused a growth in infrastructure, which would have a knock-on effect for light pollution.
We needed a further opinion. So we turned again to Dr. John Barentine and Bob Mizon MBE FRAS, and also to Professor Martin Morgan Taylor. These established experts verified our research and helped us better understand the causes of our findings.
For example, the experts explained that while there are more streetlights, many modern designs feature guards that direct light towards the ground. This helps prevent light escaping into the atmosphere and causing Skyglow.
Region by region, the UK was experiencing a decrease in light pollution. Here are just a few of the statistics we discovered.
- North Scotland down 40%
- The West Country down 41%
- Northern Ireland down 32%
- Yorkshire down 29%
- London down 14%
If the trend continues at the current rate, our data projects a further 21% decrease in light pollution between 2015 and 2025.
See how UK light pollution has changed – and use Skyglow
Skyglow didn’t end with the results. In many ways, this was the beginning.
The next step was to present our findings in a way that would help us raise awareness of the issue.
You can see our work at www.hillarys.co.uk/skyglow/ and use the interactive maps we created to show how UK light pollution has changed. You’ll also find out more about the project. We hope you enjoy Skyglow.
Note from the editor
1 – After the publication of the post, we have some comments from scientists pointing out that the study could be biased because the satellite data used might be no sensitive to LED lighting and to study skyglow measure consider surface light is not sufficient. For more information, see http://www.mdpi.com/2072-4292/7/1/1.