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Highlands Astronomical Society

'Security' Lighting


by Andy Ferguson

For a mere £5 or so, you too can purchase a lamp whose power output (500 watts) is half that of the brightest lighthouse in the U.K. They must be really effective as I can’t remember the last time I saw a ship parked in a garden.

Click for larger imageUnfortunately, due to their cheapness, these lights are being bought by more and more people for domestic use and are being installed incorrectly, without proper adjustment and with little awareness of their effects. By design, these are actually floodlights and the shallow bowl results in a light spread of well over 100 degrees so, if the lamp is tilted from the horizontal, the light travels well beyond the bounds of your own property and usually into the sky as well. It seems that even the simple manufacturer's instructions included with these products is too much for some people to read.

Almost invariably, these lamps have several things in common at each domestic location:

They face away from the house to which they are fitted. This ensures Click for larger imagemaximum annoyance of neighbours/passers-by and doesn’t disturb the owner by their own light shining through their curtains when they’re trying to get to sleep. It also ensures that anyone looking in the direction of the light cannot see beyond it, due to the glare. This is a boon for burglars who can work in the shadows you can’t see into because you’re blinded. Think of driving at night when you haven’t seen another car for some time and then a car comes round the bend on full beams. What can you see, apart from the lights? Nothing. Nada. Zip. Car headlamps are only 55 watts each, not 500. For an excellent demonstration of the effects of floodlights at differing angles, have a look here.

You may think that your light will attract attention if it comes on during the night. Not so! The Infra Red Detector (P.I.R.) fitted to these lamps is almost never set correctly to detect humans but responds beautifully to cats, dogs, hedgehogs, marauding hamsters, etc., with the result that the light comes on so often that it becomes ignored as a nuisance. Do you still react when you hear a car alarm go off? When was the last time a cat or dog was charged with breaking and entering?

Click for larger image of the view from my drivewayThe duration and/or dusk sensors are usually also incorrectly set, meaning lights come on in broad daylight and stay on for an excessive time. Many of these lights are used as glorified porch lights – why do you need 500 watts when 60 or 100 would do? Would you leave half a bar of the electric fire on for no reason? Electricity normally requires the use of fossil fuels in its generation, so you’re also damaging the environment. If you want to get rid of money, dump the light and donate to charity.

Astronomers are particularly affected as excess light leaking into the sky prevents them from seeing all but the brightest objects, especially from towns. Illumination of the night sky should be left to the rightful owners – the Moon and stars. When did you last see the majesty of the Milky Way from town? Fortunately legislation has been proposed to limit these lights but, if you have a problem with one at the moment, you can complain to the Environmental Department of the Council for action to be taken against light trespass. If you really must have an external light, please use a sensible wattage (no more than 120W), use proper settings and make sure you only light your own property. Keep the skies dark and your local astronomer will be more than happy to let you see what you’ve been missing!

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