Light Pollution and Dark Skies - Causes and SolutionsLight pollution is any source of artificial light that shines outside the area it is intended to illuminate and is a growing problem.
This article is part of a series of articles. Please use the links below to navigate between the articles.
- A Beginner's Guide To Observing The Night Sky - Stargazing!
- Tips for Improving Your Dark Eye Adaptation in Low Light Conditions
- Light Pollution and Dark Skies - Causes and Solutions
- How to Use Star Charts, Planispheres and Star Hopping
- Top Tips for Binocular Astronomy to See The Night Sky
- The Ultimate Guide to Moon Watching and Observing the Moon
- Tips for Buying Your First Telescope - What Type? How Big?
- What to Expect From Your First Night With Your First Telescope
- Sky Orientation through a Telescope
- Polar Alignment of an Equatorial Telescope Mount
- Everything You Wanted To Know About Telescope Eyepieces
- Which Astronomy Filters To Use For Astrophotography and Observation
- How to Photograph Constellations and Starry Nights
In the words of Sir Patrick Moore: "Light pollution is increasing. Unless something is done, future generations may never see the stars."
What is Light Pollution?
Both the British Astronomical Association and the Campaign for the Protection of Rural England (CPRE) define light pollution as any origin of artificial light that shines outside the area it is intended to illuminate. This includes light that is directed above the horizon into the night sky, creating skyglow, or which creates a danger or nuisance by glare. Skyglow is the light that catches particles in the atmosphere, creating an orange halo of light above a town or city at night and blocking out the stars. Figures from the CPRE show an average increase in skyglow of 24 per cent between 1993 and 2000 for the UK with street lighting and floodlighting generally to blame.
While it is possible to see magnitude +6 stars from dark sites, city dwellers are restricted to magnitude +3 at best. The light that has taken many millions of years to reach us from space is blocked in the last milliseconds of its journey due to light pollution. Naked-eye objects are reduced to binocular objects, and the beauty of the Milky Way is rendered invisible from city skies. Powerful 500-watt floodlights, often misleadingly named "security lights", are a common cause of light pollution, as are sodium street lights a cause of light pollution.
Types of Light Pollution
Light pollution can come from any type of light, but the main forms are shown below.
Uplighters are usually used to illuminate historic buildings or landmarks. Low-powered lights may cause minimal light pollution however most are overpowered and represent a considerable source of light pollution.
Recreational floodlighting, such as that used on playing fields, is often very powerful to provide adequate lighting for participants and spectators and causes significant light pollution. Thankfully these lights are not on all night or every day.
Floodlighting used as a security light is usually overpowered and badly aimed. Glare caused by poor positioning can actually aid intruders rather than deter them.
Car park floodlights are usually overpowered and poorly directed with most of the light reflected into the sky.
Effects of Light Pollution on the Nights Sky
In the photograph above you can see how different types of light create glowing skies as the light is reflected on the clouds. When the skies are clear, the light is still reflected from particles in the atmosphere which limit the amount of light we can gather in telescopes and cameras. The orange glow is from traditional sodium street lighting, whilst the whiter glows are from high-pressure sodium, tungsten or newer LED lighting.
The Bortle Scale for Light Pollution
If you're a fan of stargazing, you may have heard of the Bortle Scale. This tool is used to measure the darkness of the night sky, which can help you find the best spots for observing the stars. The Bortle Scale is a nine-level system that measures the brightness of the night sky. Level 1 represents the darkest skies, with minimal light pollution, while level 9 represents the brightest skies, with heavy light pollution. By using the Bortle Scale, you can find areas with darker skies, which will allow you to see more stars and other celestial objects. It's important to note that the Bortle Scale is not perfect and can vary depending on factors such as weather and time of year, but it's still a useful tool for stargazers.
Using the Bortle Scale to find dark sky locations for stargazing not only enhances your viewing experience but also contributes to reducing light pollution. Light pollution not only affects stargazing but also has negative impacts on wildlife, human health, and energy consumption. By choosing to stargaze in areas with low light pollution, you are helping to preserve the natural beauty of the night sky for future generations.
Use online tools such as the Light Pollution Map (shown above) to find out where you score on the Bortle Scale and to find dark skies nearby.
To find dark sky locations for stargazing, start by looking for areas with low light pollution. Use the Bortle Scale to identify areas with a rating of 3 or lower, which will have the darkest skies. Look for locations away from cities and towns, such as national parks, forests, or rural areas. You can also use online resources, such as Dark Sky Finder or the International Dark-Sky Association, to find recommended stargazing locations near you. Remember to always check weather conditions and plan your trip accordingly for the best stargazing experience.
Light Pollution Filters for Astronomy
For astronomical imaging, there is a series of astrophotography filters available which help reduce the effects of light pollution. They work by blocking the very narrow bandwidth that streetlights emit. Unfortunately, they also slightly reduce all light entering the telescope or camera so you'll need longer exposures as a result.
Light Pollution Filter is my most used filter. This filter is fantastic for reducing sky glow caused by street lighting and greatly increases the length of exposure before the photograph is washed out. Compare the "before and after" images below of the Great Orion Nebula with and without a light pollution filter.
The filters have a strange mirror finish, in some lights it is silver and mirror-like, while in other lights it is blue/purple/red "flip" and translucent. Looking through the filter by eye and everything takes on a green hue.
The comparison samples below were both taken with a Canon 350d, Skywatcher StarTravel 102 @ Prime, 30s @ ISO1600.
You can also use photo editing tools such as Lightroom or Photoshop to correct orange tints and gradients.
Light Pollution and your Environmental Health
If you're a victim of nuisance lighting and light pollution you can now report the matter to your local environmental health office which is part of your local council. The officer, after trying mediation, will then have to decide, based on the new guidelines, whether the lighting could be a nuisance. If it is then the officer will ask for the nuisance to be reduced or removed, for example by angling the offending light downwards. If the perpetrator fails to do this, the officer may take the matter to court and the perpetrator may be ordered to abate the nuisance and possibly fined. Unlike the old law, all of this will be without financial cost to the victim.
If this does not have a satisfactory outcome, section 82 of the Environmental Protection Act 1990 provides a victim with the right to a private action in a magistrates court if they feel their environmental health officer has failed to act. The magistrates will need all the relevant facts, including the local authority's view, so this kind of private action is not a failsafe.
Court action should not be regarded as an initial step. Instead, if you are a victim you should first try to discuss the nuisance with your neighbour. A negative or abusive reply from them provides further evidence for use in court. If you are assigned an environmental health officer, he or she will expect you to try mediation before court action. Although the statute is silent on street lighting, it is not expressly exempt, but it is unlikely that the provisions will apply.
Light Pollution and the Clean Neighbourhoods and Environment Act 2005
Early in 2006, the first UK law expressly aimed at tackling the problem of light pollution came into effect. The Clean Neighbourhoods and Environment Act 2005 makes "exterior light emitted from premises to be prejudicial to health or a nuisance" a criminal offence. It adds exterior lighting as a potential nuisance given the Environmental Protection Act l990, along with already recognised nuisances like noise and odours.
Under the new law, the state takes on the burden of the action and prosecutes the perpetrator. This is preferable in some ways but comes at a cost. To be a criminal statutory nuisance, the offence must be damaging to people's health or interfere with a person's legitimate use and enjoyment of the land and be more than just an irritant. It must also come from legally definable "premises" to invoke the criminal law.
What's Included and Excluded in the Law
| Included | Excluded |
|---|---|
| CONSUMER LIGHTING This is covered and includes 500-watt "security" lights. Skybeams may also be covered, but the local authority must be convinced that your property is adversely affected. | STREET LIGHTING Street lighting is not expressly excluded, but it is likely to conform to the legal definition of premises, and so will probably escape liability. Many cities are replacing their streetlights with better designs that minimise light pollution by emitting no light above the horizontal. But the new brighter lights are often on longer poles and may shine into windows, or across gardens, creating a glare nuisance. This is a gain on one hand and a loss on the other. |
| PREMISES The sorts of premises from which light will be covered include houses, blocks of flats, shops, supermarkets, shopping centres, office blocks, pubs and car parks (public as well as private). | EXEMPTED PREMISES There are several exempted premises under section 102(4) of the Act: airports, harbours, railway or tramway premises, bus depots, public service vehicle operating centres, goods vehicle operating centres, lighthouses and prisons are all outside the legislation. The reason for the exemption is that these premises need lighting for operational and safety reasons. |
| SPORTS GROUNDS Other business premises and sports grounds are included in the Act, but have the defence of "best practicable means", This means that, legally, there is no nuisance if all reasonable steps have been taken to minimise the nuisance, but the purpose of the light trumps the remaining nuisance. The attitude of both local authorities and the courts in interpreting what may constitute a nuisance or "best practicable means" is fundamental to the success of the new law. |
How to take Action against Light Pollution
Step 1
Talk to your neighbour; many may be converted if they're invited over to observe and see first-hand the nuisance they're causing. In one case, a neighbour was found to repeatedly put their lights on to 'help' an astronomer see what he was doing! Also, consider mediation rather than court action, which could lead to a feud.
Step 2
Use the new law and complain to your local authority's environmental health office. Think carefully about your complaint and give clear reasons why your health - or enjoyment of your property - is being adversely affected; for example, the light may stop you from sleeping, or it may shine across your observatory.
Step 3
If your local authority will not act, you can bring a statutory nuisance case to a magistrates' court yourself under section 82 of the Environmental Protection Act 1990. The magistrates will ask why your local authority did not act and may be swayed by this.
Step 4
If all else fails, use private nuisance in common law. You will have to prove on the balance of probabilities that the light is a nuisance. One defence is the "hypersensitive complainant", where your neighbour alleges you are being unreasonably sensitive in looking at the stars.
Step 5
Often, the solution to light nuisance is to angle the light downwards, but if all other means have failed, see www.courtservice.gov.uk for details about suing. You could even consider taking out an ASBO, as this can be granted to individuals as well as local authorities.
