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Light Pollution

Light Pollution is the bane of the astronomer but also has far reaching effects beyond upsetting the astronomical fraternity! So what is light pollution? Well, if you are out in the coutryside or at sea and you look back over a town or city you will see a glow (usually orange from the street lights) over the area - this is actually referred to a Sky Glow. If you are in the city then there is so much light being shed skywards that all the faint stars disappear, only the Moon and the brightest planets and stars remain visible. Here's a video from which highlights the problem and not just to astronomers...

Light Pollution is also defined as Light Trespass i.e. light shining on other properties or Glare - that is light shining directly into your eyes .

The lights are on all over the world! The picture above (courtesy of NASA) shows the artificial lights shining into the night sky from all over the inhabited world!

Effects of Light Pollution

So does this matter to anyone but astronomers? Well it does seem rather sad that whole generations of city dwellers have grown up without the experience of just looking up and seeing the Milky Way but it goes way beyond that!

In our carbon emitting energy conscious world the amount of energy we are wasting lighting up the sky is phenomenal!

As for wildlife, light pollution can cause migrating birds to collide with lighted buildings; cause a false dawn which disrupt birdís behaviour; cause moth deaths as they are attracted to the light (possibly a factor in the recent decline in urban moth populations) and disrupt tree and plant habits that are controlled by day length (e.g. leaf fall and flowering) in cities.

Reduction of Light Pollution

It's quite simple really. Instead of letting all the light escape upwards where no one needs it - which also creates pools of light and deep shadows down here where we need it - design lights that stop spillage from the top and sides and then point the lights downwards where we DO want the light and that eliminates much of the shadows as well! The added bonus is that because the light is being concentrated where it is needed the wattage needed per light is much less, thereby saving energy!

Abacus Lighting who manufacture energy efficient well designed lights use this picture (below) to show the effect of good lighting

You can see that the illumination on the ground is very bright and even but the sky above is dark - no sky glow! Traditional flood lighting in the situation would have caused sky glow and glare, shadows underneath and used far more power.

So what else can we do? Well before going to the expense and effort of installing lighting there are a few simple questions that can help with the process:
  1. Is lighting necessary at all?
  2. Could safety or security be achieved by other measures, such as segregation or screening of an area?
  3. Do the lights have to be on all night? For example, over advertising hoardings, the interior or exterior of buildings or empty car parks.
If lighting is the best option then only the right amount of light for the task should be installed. Lighting will then only become a problem if it is poorly designed or incorrectly installed.

So in summary:
Use lights only when and where necessary, shield or recess light bulbs to prevent spillage and glare, aim fixtures downward so there is no upward spill of light or light trespass, use low wattage energy efficient light bulbs, and finally turn off lights when they are not needed .


International Dark Sky Association working to preserve and protect the nighttime environment and our heritage of dark skies through quality outdoor lighting.

Save the Night in Europe information on the problem of light pollution in the European Union and on its possible solutions.

The Campaign for Dark Skies the British Astronomical Association"s Campaign for Dark Skies

Sydney Outdoor Lighting Improvement Society has successfully been tackling light pollution since 1998

If you run a campaign to improve our night skies and would like us to link to you then please Contact us

With all the concern about our so called our "carbon" emmissions surely now is a great time to turn off our lights and reclaim our night sky?

On average, 30% of the light from a streetlight shines upwards and outwards.

The light wasted by the UK's 9 million streetlights costs £110 million a year in electricity bills more..