This night methinks is but the daylight sick

The growth of cities these days is not to be measured simply on the ground: their wasted light spills out across the night sky like a fluorescent stain. Setting out from Spiddal the other night to travel home through the Connemara mountains, I was shocked by the pall of orange light reaching out from Galway. But that's nothing, I'm told: you can stand in the dark in the middle of Clare and see the Burren hills silhouetted against Galway's skyglow, and then swing round to find Limerick burning bright some 50 km away to the south. On a satellite photograph of Ireland at night, the great white blurs of Belfast and Dublin find answering flares in the west from Derry down to Bantry.

On an island where the coming of light has so often meant "progress", it can be hard to press the case against light as pollution. Yet that is what it has become, and not just for astronomers. The loss of the night sky in its full starlit brilliance is a theft of half of our environment - the inspirational dome of humankind.

I count it a great privilege to stand in the garden, head back, and look across millions of years of the universe. Many city people have forgotten what a truly starry sky looks like, and literally cry out in wonder when, in remote countryside, they are suddenly gobsmacked by the heavens arching above them. How many children grow up knowing space and infinity, the distant, misty galaxies, only from computer simulations or television or planetariums?

Yet, even in the countryside, true darkness is vanishing fast. A handful of brutal outlaws have ended the innocence of the Irish night forever, and made darkness a thing of fear for thousands of people who live off the beaten track. Dazzling, 500-watt security lights now blaze at the gables of farmhouses and retirement bungalows on every minor road. Street lighting, too, is taking on the function of a reassuring night-light. In Co Tipperary last month, a woman living five kilometres from the nearest village, a lover of night and nature, was appalled to find a lone orange sodium street-light suddenly blazing from an ESB pole across the road. Her elderly neighbour, it seemed, had requested it from the county council, whose roads section was happy to arrange it for a modest payment of £200. Anyone, it seemed, could ask the same, and the star-gazer's protest to the roads engineer was met with the reproach of selfishness for "denying a pensioner on her own a bit of light". The problem, manifestly, is going to grow, as vastly overpowered, unshielded lights proliferate through the countryside, utterly changing its night-time character as well as adding to the general diffusion of waste light into the sky.

Ireland will forfeit the intervals of mystery and imagination, of rural chiaroscuro, that separate the country from the town. Twilight and daybreak, moonlight and its shadows will be bleached from our encounters with nature. Such experiential values, however whimsical they may seem at an engineering level, deserve to be part of our quality of life.

The crusade against light pollution, now under way in several western countries, points to the wasted energy and poor design inherent in skyglow. In Britain, the Campaign for Dark Skies (at www.dark-skies.freeserve.co.uk/) was set up 10 years ago by members of the British Astronomical Association. Its network of almost 100 volunteer local officers works to persuade local councils and organisation s of the benefits of well-directed lighting at appropriate intensities.

Lighting engineers have been responding well, having little stake as a rule in wasting 30 per cent (and often much more) of a lamp's output on the stars, and lobbying of government ministers has helped to produce a national shift in policy. Full-cut-off or sky-friendly lighting is now standard in new and refitted road-lighting and manufacturers are competing to refine new, downwardly-focused designs which make better use of fewer watts.

In Ireland, technical advice from the Campaign for Dark Skies was considered in an evaluation of lighting costs at the time of the Rainbow Coalition, but there is still no policy on light pollution.

In some small towns, however, local authorities have shown considerable sensibility in lighting levels. The warm illumination of reproduction-Victorian street-lamps in the Mayo tourist centres of Westport and Louisburgh, for example, is a welcome move - a theme park reinvention, but who cares?

Even small villages, for whom a row of sodium street-lamps has been a token of political attention, may ultimately tire of their relentlessly lurid glow. In one or two English villages (of the up-market kind, presumably) the inhabitants have rejected the full lighting scheme proposed by the county council, preferring to fork out for their own Victorian lamps, or even agreeing to keep their 40 watt porch lights burning as an adequate level of street-lighting.

In the countryside and on city fringes the problem, increasingly, is private security lights of factory-yard wattage, left blazing as the equivalent of a snarling rottweiler. The Campaign for Dark Skies recommends the well-aligned security light, of a perfectly-adequate 150 watts, triggered by infra-red sensors (and thus, alas, not infrequently, by a wandering sheep or fox), but it just doesn't have the same deterrent appeal.

On this Christmas Eve, as candles glimmer bravely in the townland windows, we shall see them as a poignant celebration - not least of the gift of darkness.

Edited by Michael Viney, who welcomes observations sent to him at Thallabawn, Carrowniskey PO, Westport, Co Mayo. Email: viney@anu.ie (E-mails should include a postal address.)