Light Pollution

What is Light Pollution?

Simply put, light pollution is wasted light. This may be a 'security' floodlight shining in a bedroom window. Or it may be a streetlight spilling light into the sky dimming out the stars.

It can be classified into three forms:

• Sky glow is the orange glow that can be seen in the night sky above cities and towns. Any light shining over the horizon contributes to this glow and the effects can be seen many miles from the polluting lights. Streetlights are the main cause of sky glow.

• Glare is light shining into the eye preventing a person from seeing the illuminated area properly. For example, an over-powerful 'security' floodlight at the wrong angle.

• Light Trespass or Light Nuisance is where a light is not only illuminating its target area, but also lighting another area where it is not wanted. This is most commonly found with security floodlights shining over a wide area.

Light Pollution Pattern And Effects
(c) Institute of Lighting Engineers

Why should I care about light pollution?

Better lighting saves money. Whether it is a badly designed streetlight, or a security floodlight in your home, money is being wasted. Using a correctly fitted exterior light with an appropriate wattage can reduce the running costs of the light by 70%. By fitting a sensor so that the light is only on when needed, the savings are even more.

Changing your exterior lights to more efficient designs will pay for itself. With electricity prices in Ireland rising can you afford to ignore light pollution?

Better lighting aids visibility and so may help reduce crime.

Better lighting helps the environment. Wasted light is wasted energy and that energy is produced mainly by the burning of fossil fuels: using more efficient lighting results in less energy being needed and less carbon dioxide being released into the atmosphere.

Bad lighting causes negative effects on wildlife. Birds in your garden will be affected by bad security lighting, or even worse, by 'decorative' floodlighting illuminating trees from the base. The effects of this can be seen by birds feeding and singing after dark; their natural cycles are disturbed by strong artificial lighting.

Better lighting lets us appreciate the night sky. From our cities we can at most only see a few hundred stars. In rural areas thousands of stars are visible and our home galaxy, the Milky Way, is a glorious sight meandering across the sky. The 'Leviathan of Parsonstown' telescope in Birr, Co. Offaly, was once the largest telescope in the world. Observations through the telescope changed the way we see the world and the names that the Earl of Rosse gave objects he saw are still in use today. It would be tragic to lose our astronomical heritage because our children can no longer see the stars.


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