Light Pollution - Q & A

Q. What is light pollution?
Q. What causes light pollution?
Q. What does light pollution affect?
Q. Is astronomy alone affected?
Q. Does it affect other living things?
Q. Does it affect the environment?
Q. Do security lights prevent crime?
Q. Does lighting make night safer?
Q. Can light pollution be controlled?
Conclusion
About this article

Q. What is light pollution?
A. Simply put, light pollution is light that is allowed to go where it is unwanted. Light pollution is often referred to as "skyglow" and "light trespass". A common misconception is that the only thing that humans have created which is visible from space is the Great Wall of China: It is in fact the light we send upwards from our planet at night. Satellite images of Earth show a tremendous variety of features, but one might think that images showing parts of Earth during the hours of darkness would be unrecognisable. The sad fact is that they are often very easily recognisable because of artificial light.

Q. What causes light pollution?
A. Unnecessary, or excessive, or badly designed, or badly installed exterior lights that permit light to go upwards. Older street lights are a major cause of urban skyglow. In some instances, lighting schemes for streets, precincts and commercial premises are simply 'over the top' and indiscriminate to no overall gain and are simply wasteful. Illuminated signs and buildings contribute further as does uncontrolled and badly designed and installed domestic lighting. The recent trend for so-called "security" lighting has further accelerated the amount of wasteful and intrusive light.

Q. What does light pollution affect?
A. It affects every one of us, not just astronomers. Light pollution is a nuisance, it despoils the night time environment and places an unnecessary strain on precious natural resources. Light pollution makes the night sky unduly bright and can prevent stars from being seen. Astronomy from an urban site can be made impossible by the encroachment of light pollution. The night sky is a precious national and educational resource and is undoubtedly of great special scientific interest.

It is estimated that at least 50% and possibly as much as 90% of the UK population is affected by light pollution. To truly appreciate the night sky one may have to travel many miles from a built-up area to see a truly dark night sky. Most major astronomical observatories are now located in dark, sparsely populated areas and in some cases have been forced to move to other countries because of increasing light pollution from built-up areas. All this means that many people have difficulty with or are prevented from enjoying one of nature's greatest free spectacles - the sky at night!

Q. Is astronomy alone affected?
A. No. Excessive or bad lighting affects all living things. All exterior lights, in particular domestic floodlights, are a common source of nuisance if they shine into a neighbouring property. This type of nuisance currently has no legal controls. Light pollution affects people and their interests but it also affects animals and on a broader scale the environment. Therefore, light pollution should be of concern to everyone.

Q. Does it affect other living things?
A. Yes. It is estimated that every night, somewhere in the UK, 10 000 Robins serenade a false dawn caused by artificial light. The number of other songbirds that are affected may be innumerable. Generally, if you hear birds singing at night it is because of artificial lighting. Studies of migratory birds have shown that they may be stimulated into premature migration because of artificial lights. Deciduous trees that are subjected to artificial light have been shown to retain their leaves in winter on the side that is lit at night. These are just a few examples of how lights can affect living things.

Q. Does it affect the environment?
A. Yes, wasted light means wasted energy. A conservative estimate indicates that 53 million (early 1990's figures) is wasted annually in the UK and that the true figure may be much more than that. This is taking into account street lights only and not other form of lighting. A recent study in the United States indicated that over $2 thousand million of electricity is wasted annually because it is allowed to go upwards.

About 25% of all global greenhouse gas emission is caused by domestic energy consumption. A study and project in the United States is under way and has already shown that if "green lighting" was installed in the US, $16 thousand million could be saved every year. This amounts to 12% of all US carbon/sulphur/nitrogen dioxide emissions.

Q. Do security lights prevent crime?
A. There is no evidence that "security lights" deter criminals. A majority of studies in the US show no significant link between crime rates and extra lighting. Studies in the UK have had similar results. Most studies of this kind indicate that the fear of crime is reduced but the actual crime rate is not. It is worth noting that about 60% of break-ins take place in daylight, don't forget that criminal have to see as well! Several projects and studies in US schools, colleges, and universities have shown that vandalism actually decreases when lights are switched off at night.

Poorly designed and installed lights are ineffective and can be dangerous in some cases. For example, an excessively bright or poorly aimed light may dazzle onlookers who might otherwise report a crime in progress. Lighting up a secluded area may act as a courtesy light for a would-be criminal and may even tempt criminals by making the area more visible. Insurance companies may offer discounts for high security locks but they do not offer discounts for the installation of so-called security lights.

Q. Does lighting make night safer?
A. Yes, in some cases it does. Some lighting is useful for road safety, on the street for pedestrians, so that we can see in our homes. But this does not mean that we should light everything, everywhere, this is just wasteful. There are some studies that show that lighting can effect a small decrease in accidents at known black-spots. It may be that lighting can decrease accidents at certain places, but excessive, poorly aimed lighting and the glare that it causes may be counterproductive and expensive.

Q. Can light pollution be controlled?
A. Yes it can, but only by education and legislation can the trend towards more and unnecessary lighting be halted and reversed. For example, the UK Highways Agency has stated that future A and M Road schemes will be lit by "sky-friendly" fixtures. New and replacement street lights now feature "full cut-off" that prevents almost all light from escaping above the horizontal. Unfortunately, there are no legal controls applicable to domestic lighting at the moment. Regulation can halt this trend. Education can alert people to the scale of the problems of light pollution.

Conclusion.
All this may suggest that astronomers want all lights switched off - this is not true! We want to see the promotion and installation of good lighting. Lighting that is not too bright, does not blot out the night sky and waste energy. Lighting that is sensible, economical, properly installed and regulated. We would like to see the night time environment and Earth's resources preserved for future generations. The light from stars and the universe can take millions of years to reach us - only for it to be lost on the very last moment of its journey!

About this article. . .
This article was written by Derek Haselden with the assistance of Bob Mizon (Wessex AS), Co-ordinator of the Campaign for Dark Skies (CfDS). Much of this article came from Campaign for Dark Skies and the International Dark Skies Association material.