01/
On a clear, dark night it’s possible to view somewhere in the region of 4,000 stars. The number of stars we can see at night depends largely on the amount of light we emit from the Earth’s surface.
Artificial light that’s excessive, obtrusive and ultimately wasteful is called light pollution, and it directly influences how bright our night skies appear.
With more than nine million streetlamps and 27 million offices, factories, warehouses and homes in the UK, the quantity of light we cast into the sky is vast. While some light escapes into space, the rest is scattered by molecules in the atmosphere making it difficult to see the stars against the night sky. What you see instead is ‘Skyglow’.
The approx. number of stars visible in a clear, dark sky from earth
4,000
Lighting up the UK
No. of Streetlights
9,000,000
No. of Homes
25,000,000
02/
Using images from overhead satellites, we looked into how bright our night skies appear from space, and how this has changed over the last 22 years.
We used images from two different satellites, the Operational Linescan System (OLS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) to calculate the brightness of the night sky.
Total brightness today
2,713 million Lumens
28%
Total brightness today
79 million Lumens
40%
Total brightness today
47 million Lumens
41%
Total brightness today
112 million Lumens
28%
Total brightness today
264 million Lumens
29%
Total brightness today
114 million Lumens
32%
Total brightness today
196 million Lumens
38%
Total brightness today
365 million Lumens
29%
Total brightness today
410 million Lumens
25%
Total brightness today
171 million Lumens
31%
Total brightness today
449 million Lumens
14%
What is the projected percentage change in brightness for the next two decades?
03/
You can see from the map that between 1992 and 2012 ‘Skyglow’ decreased by 28%. This is surprising since the UK population increased by 10%. One possible conclusion is that ‘Skyglow’ has reduced because we’re using better designed lighting that doesn’t create as much light pollution. Another possible cause is that overall we’re consuming less energy. However, the rise of energy efficient lighting may mean we’re still generating the same amount of brightness.
It’s important to remember that just because the average amount of ‘Skyglow’ has gone down across all regions, certain areas within regions may have actually increased in brightness. This would be offset by other areas getting darker. This could happen, for example, if there was a migration of people from one location to another.
A contributing factor to the decrease in light pollution, despite the population increase, could be the rise in multiple occupant housing. If people are relocating from rural to city locations, clustering in specific areas and living in more crowded conditions, this could cause light pollution to be higher, but confined to a smaller area. This would be countered by a much lower level of light pollution in areas outside of this concentration. Overall, this has the potential to lower the average level of light pollution.
04/
When we consider the damage of other types of pollution, ‘Skyglow’ may seem relatively harmless. However, the damage is far reaching, affecting plants, animals and humans in a number of ways.
“Lighting up the world carelessly leads to the waste of energy and money, along with significant costs to our quality of life. Our biology and ecology remain ill-equipped to handle night time brightness in extreme measures, and can suffer even in the presence of relatively small amounts. We encourage everyone, from property owners up to governments, to consider carefully the need for artificial light at night and to ensure that any light used is the proper amount, at the proper time, for only the task at hand. The need to light our activities can be balanced with preservation of the night through simple acts such as shielding light fixtures and lowering light intensities to appropriate levels.”
Dr. John Barentine from the International Dark-Sky Association (IDA)
WHAT DOES LIGHT AFFECT?
Brain wave patterns
Hormone Production
Cell Regulation
How much of our DNA is controlled by the circadian clock?
10-15%
DISCLAIMER |
Data was taken from two satellite types, the Suomi NPP (VIIRS) and the DMSP (OLS).
The OLS took images of night-time brightness between 1992 and 2012. Each year represents a composite of hundreds of images converted into one. Images from 2013 onwards are regionally separated projections of OLS data. The projected change is based on current trends of satellite observed lighting released by the NOAA, and does not take into account other future variables.
Regional classifications are based on the scope and surface area of UK TV regions. Percentage change in average regional brightness is calculated using pixel saturation data and total number of pixels per region. These percentages were based on data from the OLS only, from 1992-2012 and projected to 2015 and 2025. Brightness levels within a region may be higher or lower than the regional average.
Total brightness in lumens relates to high-resolution VIIRS data from 2014. It was calculated by converting average regional brightness in lux to total lumens per region using surface area data by TV region. Lux was calculated on the assumption that the visible light is at 555 nano-meter wavelength.
Data sources were taken from the National Geophysical Data Center (www.ngdc.noaa.gov). For additional sources, regional statistics and queries please contact [email protected]
THANKS |
Hillarys extend their thanks to contributors Jurij Stare of Dark Sky Slovenia, Dr. John Barentine from the International Dark-Sky Association, and Bob Mizon MBE FRAS, Coordinator of the British Astronomical Association Campaign for Dark Skies.
Hillary’s would also like to give a special mention to the work and direction of Christopher D. Elvidge of the Earth Observation Group at NOAA National Geophysical Data Center, Kevin Ward at NASA’s Earth Observatory and Emma Marrington from the Campaign to Protect Rural England (CPRE).
FOOTNOTES |
* Light bulb comparisons are calculated using an example 60 Watt bulb of 840 lumens.
** Figures according to Urban Lighting, Light Pollution and Society (2014).
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