In the Garden:
North America at night is awash in artificial light.
As we head toward the winter solstice, the days are getting not only colder, but significantly shorter as well. Here in Vermont, there are more than 6 1/2 fewer hours of daylight on dark December's shortest day of the year than at the midsummer solstice. So it's likely that we are keeping our outdoor lights on for more hours at this time of year, which got me to thinking about the effects of those lights on the natural environment.
Every year, the amount of artificial light put out into the environment increases, to such an extent that in many parts of the country (and other developed parts of the world), a true view of the night sky is a thing of the past. When the 1994 earthquake knocked out power in the Los Angeles area, emergency services received a spate of calls reporting a giant silvery cloud in the sky. It turned out to be nothing more than the Milky Way galaxy, visible once again when the "sky glow" from the city no longer dimmed its view.
When unneeded or unwanted light causes adverse effects, it is termed "light pollution." Scientists are just now beginning to understand the long-term harmful consequences it can have on plants, animals and even humans. The continual twilight from artificial lights can affect the mating habits, feeding patterns and navigational ability of a number of animal species. Besides disrupting the migration patterns of some birds, it leads to the death of millions each year as the result of collisions when birds are drawn to lighted buildings. But other nocturnal creatures also suffer negative effects, including frogs, bats, sea turtles, fish, moths and fireflies, whose females only flash their lights to attract mating partners at a certain level of darkness.
And it's not just animals that are at risk. Trees and shrubs can be affected by nocturnal lighting. The photoperiod, or hours of darkness a plant is exposed to, governs a number of developmental processes in plants, including dormancy, shoot growth and flowering. So, for example, artificial light may keep a plant growing actively when it should be preparing to shut down for the winter, making it more susceptible to winter injury.
Much light pollution is the result of badly designed light fixtures that send light up and sideways, where it's not needed, rather than downward where its illumination is actually useful. According to estimates by the International Dark-Sky Association (IDA), a non-profit organization whose mission is to preserve and protect the night-time environment through environmentally responsible outdoor lighting, about a third of all outdoor lighting is "wasted" by being directed upward and sideways. This not only causes light pollution, it amounts to an annual cost in the U.S of about $2.2 billion, and the resource use and pollution equivalent to burning 12.9 million barrels of oil or 3.6 million tons of coal.
So what can you do to help decrease the hazards associated with light pollution to your landscape plants and the environment in general? Of course, much of the problem is caused by municipal and commercial lighting, so you can encourage your community to adopt dark-sky friendly lighting ordinances. The IDA Web site at http://www.darksky.org has suggestions for local action, as well as guidelines and a sample model lighting ordinance.
But you can also help by taking light pollution into account in the design and use of your own landscape. Start by turning on outdoor lights only when you need them and turn them off when they are no longer needed. Using motion sensors and timers can be very helpful in this regard. Close your blinds or curtains at night so indoor light remains inside and turn off lights when you leave the room.
Choose properly designed light fixtures that are shielded to direct light where it's needed, and don't use more wattage than you need. Check for the "IDA Approved Dark-Sky Friendly Fixture" label when you are shopping for outdoor lighting. The IDA Web site includes lots of helpful information on minimizing light pollution and selecting well-designed light fixtures and includes a downloadable guide for homeowners on environmentally friendly residential lighting.
Then go out in the dark and look at the stars!
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