Q. What is light pollution?
A. Simply put, light pollution is light that is allowed to go where it is not wanted. Light pollution is often referred to as "skyglow" and "light trespass". A common misconception and frequently quoted urban myth 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 all too easy to recognise because of the artificial light that is poorly used and allowed to 'leak' upwards. Major cities, towns, motorways, roads and many other man-made features are all clearly visible from space nowadays due to wasted light. And the problem appears to be getting worse.

Q. What causes light pollution?
A. Any exterior light source that permits light to go upwards or where it is not needed:

Unnecessary - Lights that have no useful purpose or are lit when not needed.
Excessive - Lights that are too numerous or simply too bright.
Badly designed - Lights that are not properly shielded or have no shielding at all.
Badly installed - Lights that are poorly directed or situated.
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.


Q. What does light pollution affect?
A. It affects each and every one of us, not just astronomers. Light pollution is a nuisance, it is wasteful and despoils the night time environment and places an unnecessary strain on the planet's 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 near 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.

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. There are also growing medical concerns as to the health effects of too much light at night, after all, humans are not naturally nocturnal creatures. 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 has been observed and that in night, birds serenade a false dawn caused by artificial light. The number of other songbirds that are affected may be innumerable. There has been studies by RSPB (Royal Society for the Protection of Birds) and they suggest that the decline in numbers of many birds in recent decades may be due to the proliferation of night-time lighting. Generally, if you can hear birds singing at night it is because of artificial lighting - it is not normal or natural. Studies of migratory birds have shown that they may be stimulated into premature migration because of artificial lights. Lights can confuse creatures, especially birds, and cause them to blunder into buildings. 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. Moths and other insects appear to be confused by bright exterior lights. Many creatures are nocturnal by nature and excessive night-time lighting will almost certainly affect them in some way. These are just a few examples of how lights can affect living things.

Q. Do security lights prevent crime?
A. This is one of the most contentious and emotive aspects of light pollution and is worth exploring in greater detail. There is no evidence that "security lights" deter criminals. It seems to be perceived wisdom and belief that a light will deter or prevent a crime. But 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. A recent study in the UK of lighting and crime proclaimed that additional street lights caused a large reduction in crime statistics. However, independent analysis of that study's findings found that the data collection and overall analysis was flawed, invalidating the study's conclusions. It is worth noting that the study was in fact funded by a lighting manufacturer.
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 over half of all break-ins take place in daylight, don't forget that criminals 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 see and 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. For example, in UK a Dorset secondary school was never broken into for about 20 years since its inception, being set back from the road behind trees and unlit. Soon after sodium lights were installed all around the building, it was broken into, not once but several times in the next few years. As if to emphasise how little effect security lighting has, insurance companies offer discounts for high security locks and professionally installed alarms but they don't offer discounts for the installation of so-called security lights.

As mentioned further up this page, a single 500 watt lamp left on all night creates 1.25 tonnes of Carbon Dioxide annually at the power station burning fossil fuels to keep it alight. If, for example, the cost of
the electricity is just two pence per kilowatt hour, and the light is lit, on average, for 8 hours a day,
all year, a 500 watt lamp costs nearly £30 per year to light.

Q. Does lighting make night safer?
A. Yes, in some cases it can. 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 road lighting can effect a small decrease in accidents at known black-spots. Lighting may decrease accidents at certain places, but excessive, poorly aimed lighting and the glare that it causes can be counterproductive and expensive.

In some cases lighting can actually be dangerous. In France it is not unusual to find that some streetlights are switched off around midnight, an economy that could be used elsewhere. Clearly there is much to be considered with regards the use of light.

Q. What does light pollution cost?
A. It is extremely difficult to state just how much light pollution costs. While it is simple to say what may be lost or affected in some way, many of the things affected by light pollution are simply impossible to put a price tag on.

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. There is an international trend nowadays for road lighting to be better directed.

A country that has taken a lead in controlling light pollution is Czechoslovakia. The Czech government recently passed legislation which prohibits the use of indiscriminate lighting with fines of up to £1000
for non-compliance. Perhaps this will trigger similar moves elsewhere; one certainly hopes so for the sake of all those affected by excessive lighting.

Q. Can you make a difference?
Yes, you can make a difference to light pollution. Doubtless you will be aware of environmental issues like greenhouse gases, global warming, dwindling resources and so forth. Chances are you already take steps to reduce the impact you have on the environment - recycling, using public transport, insulation - there are many ways you can make a difference. Why not go one bit further and reduce the impact that lights have on the environment. Using low-energy bulbs, fitting lower wattage lamps, switching lights off when they are not needed.
If you do have exterior lighting consider whether you really need it. Again, it is necessary to repeat that there is no proof that lights prevent crime. If you must have exterior lighting consider what brightness it should be. Many exterior domestic lighting situations seldom require more than a few tens of watts power at most. Can the wattage of the lamp be reduced? Do you really need a 500 watt lamp when, say, 50 watts would be enough? Consider the following:

Can the light be aimed so that it shines down where it is needed?
Can it be aimed so that light does not encroach onto a neighbours’ property?
Can it be aimed so that it does not dazzle people?
Can the light be shielded to prevent light escaping to where it is not wanted?
If your own exterior lighting complies with all reasonable considerations, what about others? If your neighbour has lighting that affects you, have you considered raising the issue with them? They may be
unaware that they are causing a problem. If a neighbour has lights that you consider a nuisance you can do something about it by raising the issue with your local Authorities.

There are many ways that exterior lights can be made to have a markedly reduced impact on the environment. And it is a win-win situation. Less light means less light pollution. Reduced power consumption means less fuel consumption. Reductions in consumption mean lower bills. Everyone wins in the short and long term!