What is Skyglow?

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’.

DEFINITION | SKYGLOW : The brightness of the night sky in a built-up area as a result of light pollution.

The approx. number of stars visible in a clear, dark sky from earth


Lighting up the UK

light bulb

No. of Streetlights

building icon

No. of Homes


Mapping Light from Space

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.

Slide the scroll bar across to see how the UK’s brightness has changed from 1992 to 2012, and see our calculated projections for brightness up to the year 2025.


Use the brightness key below to compare the brightness of different regions. This will tell you the percentage change in average brightness of the UK from 1992-2012. You’ll also see the total brightness of each region as of 2014 in lumens.*

DEFINITION | LUMEN : A lumen is a measurement of total visible light from a source. The larger the number of lumens, the brighter it appears.

Brightness by Location | 2014

  • The UK
  • North Scotland
  • The West Country
  • Wales
  • Central Scotland
  • Northern Ireland
  • Anglia
  • Yorkshire
  • The Midlands
  • South East
  • London

The UK

Total brightness today
2,713 million Lumens

= The same as 3,229,996 light bulbs

light bulb

down overall by


Brightness by Location | 2014

  • The UK
  • Down by 28%
  • Total brightness today = 2,713 million Lumens
  • Equal to the brightness of 3,229,996 light bulbs
  • North Scotland
  • Down by 40%
  • Total brightness today = 79 million Lumens
  • Equal to 93,906 light bulbs
  • The West Country
  • Down by 41%
  • Total brightness today = 47 million Lumens
  • Equal to the brightness of 55,752 light bulbs
  • Wales
  • Down by 28%
  • Total brightness today = 112 million Lumens
  • Equal to the brightness of 133,184 light bulbs
  • Central Scotland
  • Down by 29%
  • Total brightness today = 264 million Lumens
  • Equivalent to 314,697 light bulbs
  • Northern Ireland
  • Down by 32%
  • Total brightness today = 114 million Lumens
  • The same as 135,710 light bulbs
  • Anglia
  • Down by 38%
  • Total brightness today = 196 million Lumens
  • Equivalent to 233,213 light bulbs
  • Yorkshire
  • Down by 29%
  • Total brightness today = 365 million Lumens
  • Equal to 434,231 light bulbs
  • The Midlands
  • Down by 25%
  • Total brightness today = 410 million Lumens
  • Equal to 487,573 light bulbs
  • South East
  • Down by 31%
  • Total brightness today = 171 million Lumens
  • Equal to 203,286 light bulbs
  • London
  • Down by 14%
  • Total brightness today = 449 million Lumens
  • Equal to 534,353 light bulbs

What is the projected percentage change in brightness for the next two decades?

UK Projected
change: down by

UK Projected
change: down by


What the Skyglow Map Shows

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.


How Skyglow Affects You?

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)


brain waves icon

Brain wave patterns


Hormone Production


Cell Regulation

How much of our DNA is controlled by the circadian clock?




YOUR VIEW OF SPACE | Of the estimated 70 thousand million million million stars in the universe, we’re lucky enough to view even a few thousand from Earth. In urban areas that number falls to just a few hundred stars - and possibly much fewer in major cities.

“Since the 1950s, a tide of wasted light has veiled the starry sky. Light travelling, even at low angles, above the horizontal scatters from dust and aerosols in the atmosphere and colours the night sky out to great distances. Most of us, not just astronomers, enjoy seeing a star-filled night sky, but even if you don't, skyglow is an obvious symptom of the waste of money and energy. There are signs that, with the new generation of strictly downward directed lights on our roads, the night sky is returning to some areas. As long as lighting is not too bright for the task (as are some of the new blue-rich LEDs), the trend will continue. But unregulated sports and area floodlights still pollute locally, and until proper regulation is in force, they will probably proliferate.”

Bob Mizon MBE FRAS, Coordinator at the British Astronomical Association Campaign for Dark Skies.

YOUR CARBON FOOTPRINT | Over half the energy we use for outdoor lighting in the EU is wasted because we’re using more power than we need. This could be due to inefficient lighting, people not turning off lights when unneeded, or poorly designed lights that lead us to use additional lighting. People living in the EU use, on average, 117 kWh per person for outdoor lighting each year. Of this, 90 kWh is used for public lighting, and 27 kWh for private lighting. Since we only need around 50 kWh for both public and private outdoor lighting, more than half the energy we use – 67 kWh – is essentially wasted. Each kWh we use creates 0.5 kilograms (kg) of carbon dioxide (CO2) and costs us around €0.11 (7 pence). This means we each waste 33.5 kg of CO2 on outdoor lighting, which costs us €7.40 per year. Multiply this by the number of people in the EU and our total carbon contribution from wasted energy amounts to 23.5 billion kg, costing us €5.2 billion (£3.8 billion) a year **.

YOUR BIOLOGY | By flooding the night skies with artificial light we’re also putting our wellbeing at risk. Since most living things run on a 24 hour day/night cycle known as the circadian clock, too much nighttime light can prove harmful to us on a molecular level. This cycle controls 10 to 15 per cent of our genes, which means brainwave patterns, hormone production and cell regulation can all be disrupted by interfering with its pattern.

WILDLIFE SURVIVAL | Life on Earth has evolved to suit its natural surroundings. It has developed to fit with and benefit from the day/night cycle of light and shade. Daylight regulates chemical reactions in plants and animals that they need to survive. Meanwhile, darkness allows nocturnal animals to safely carry out important tasks like hunting or scavenging, feeding and mating. As well as disrupting biological patterns, too much light can also cause confusion, particularly in migrating birds, which use the stars to guide their way.

Hilarys Logo
Hillarys supports Dark Skies Awareness, part of the 2015 International Year of Light.

share this
facebook twitter google stumbleupon reddit

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]

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).

* Light bulb comparisons are calculated using an example 60 Watt bulb of 840 lumens.
** Figures according to Urban Lighting, Light Pollution and Society (2014).