What is Light Pollution and Why Should You Care?

If one is lucky enough to live in a rural location you can look up on a clear night and see the Andromeda Galaxy which is 2.5 million lightyears away. That isn’t true for those that live in, or close to a town, village or city. From the heart of a city, one would be lucky to pick out the brightest of the stars in the night sky. This is due to light pollution. The most common type we are used to is the sky glow seen above cities and towns. This is caused by light scattering into the sky where it isn’t needed. Any light that is causing a nuisance can be considered light pollution. For example, a streetlight shining into your bedroom window or a neighbor’s security lighting illuminating your garden.

Clockwise from top left. Heavy light pollution, little light pollution and no light pollution. Credit: Paul Smith

This week, 5th April to 12th April 2021 is International Dark Sky Week. International Dark Sky Week is organised annually by the International Dark Sky Association to raise awareness of the effects of light pollution. We’ve all heard of pollution. Whether that be littering the environment, sound pollution or water pollution, but light pollution is often overlooked. It is often only astronomers, both professional and amateur that are concerned by it but light pollution is something we all should be concerned about.

The obvious impact is on the night sky but it isn’t the only one. Human health, climate change, wildlife, crime and safety are all affected by light pollution. Not to mention the money that is spent on lighting that is unnecessary and inappropriate.

Culture and Heritage

Much of human heritage and culture is based on the night sky. There is evidence of the pyramids in Egypt and tombs such as Newgrange being aligned to stars and other celestial bodies. Many scientists and artists were inspired by the night sky.

Human Health

Research from Harvard Medical School and the American Medical Association Council on Science and Public Health has found the light pollution effects human health. Humans have evolved to adhere to a circadian rhythm. This is an internal biological clock which is controlled by the day/night cycle of the Earth. The rise of artificial lighting has disrupted that pattern and research shows that this leads to lower levels of a hormone called melatonin. Other research has also linked various health issues to being exposed to light at night.

Climate Change

One of the biggest challenges facing the human race is climate change and light pollution is contributing to it. The department of energy in the US estimated in 2011 that 15 million tons of CO2 are produced every year to generate the electricity to power outdoor residential light. They also estimated that 35% of the streetlight was wasted as it wasn’t shining on the street where it was intended. This equates to a cost of about $3 billion dollars a year.


Just like humans, animals and wildlife rely on the cycles of day and night for many different functions from hunting to reproduction. Artificial lighting plays havoc with this, particularly as animals don’t know the difference between natural and artificial light. Have you ever heard a bird signing in the middle of the night in a city? Among the effects on wildlife are birds that have been observed wandering off migration routes due to light from cities. Another effect is insects, being attracted to artificial light sources where they would normally be food for other wildlife.

Crime and Safety

The purpose of most street lighting is to make the area safer and prevent crime but there is very little evidence to support that it does. In fact, a study in the Journal of Epidemiology and Community Health found that streetlighting had no effect in reducing crime or accidents. In Chicago, a report by the Illinois Criminal Justice Information Authority found a correlation between lit up alleyways and crime. Another concern is that badly aimed lighting may make it more difficult to see. The glare from a badly aimed light causes the pupil to contact and decreases contrast. Look at the picture bellow. Both lights are the same but the light that is aimed down is much more effective than the light aimed sideways.

Badly Aimed Security light

The solution to all of this is not to simply turn the lights off. Artificial lighting can be used while minimising the negative effects. We must of course first look at the lights that aren’t needed. For example lights on remote farm buildings may not be needed when nobody is there. They could also be put on sensors to reduce the amount of time they are on. When it comes to lighting around homes, we should ensure it is aimed properly so that it isn’t shining into the sky or into a neighboring garden. Why would you want to pay for electricity to light the sky or someone else’s garden?

Five principals of outdoor lighting Credit: Dark Sky Assosiation

Not all light fittings are created the same. Lights that are most effective and reduce light pollution are fittings that are fully shielded. This means that all of the light falls only where it is intended.

Light fittings Credit: Dark Sky Association

Industry also need to pay attention to this. Lights from factories etc. should be fully shielded and aimed correctly. There is also a role for government and local authorities to play in this. Planning guidelines should include outdoor lighting and there should be policies and laws around installing lighting outside. Local authorities should lead by example. Streetlighting and lighting on public buildings should follow best practice and this is starting to become more common with newly installed streetlights now fully shielded. More needs to be done though and we should all be pressing our local politicians to make it happen.

For millennia, humans have gazed up at the night sky, told stories, and wondered at what is beyond. The majority of people now live in areas where they will never see the sky and that won’t change unless we all do our part.

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