Regional Gardening Reports :: National Gardening Association

In the Garden:
Middle South
July, 2007
Regional Report

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Light pollution of the night sky above the Eastern U.S. is visible from space. (Photo courtesty of NOAA and the U.S. Air Force)

Let There Be Light, But Not Too Much

As we were watching fireflies the other evening I couldn't help but wonder how much brighter they'd be, and how many more we'd see, if it weren't for the nearby streetlight. Fireflies are one of those gifts of nature, like the impossibly bright plumage of cardinals and bluebirds or the incredible intricacy of a passionflower -- things that make one pause to wonder if maybe there is a guiding hand behind the evolutionary process. In the brightly lit world we live in, it would be easy to overlook the humble firefly, but to do so is to miss a miracle of nature.

Light Pollution
Air and water pollution make the headlines, but there's another kind of pollution that has an impact on us, and on the animals and plants around us: light pollution. Most of us live in cities or suburbs and have never experienced the blackness of a moonless night. When I moved from urban Boston to very rural Vermont I was awed -- and frankly a little frightened -- at just how dark it could be. So dark you couldn't see your hand in front of your face, or see where your next footstep would land. It was spooky, but exhilarating, too. It occurred to me, "It's supposed to be this way."

According to the International Dark-Sky Association, 80 percent of Americans live in areas where the night sky is so illuminated with artificial light that the effect is equal to or near that of a full moon. Only about one third of the population can see the Milky Way. About 120 million people live in areas so polluted by light that they can't see any stars at all.

Landscape Lights
Most homes have some type of outdoor lighting. A lamp post at the end of the front walk welcomes visitors; a flood light over the garage bathes the driveway in a rich glow. Walkway lights encourage sure footing from car to door; a porch light signals, "We're home." A dark house is an uninviting house.

Light has come to represent safety and security. A well-lit parking lot feels safer than a dark alleyway; a well-lit house is less likely to be burglarized. Are there ways to achieve the benefits of light while minimizing light pollution?

Types of Lighting
Landscape lights can be divided into three categories: safety, task, and accent. Safety lighting lets you see where you're going and discourages unwanted visitors. Task lighting illuminates areas where activity takes place. Accent lighting is decorative and illuminates areas of yard you want people to notice. Because landscape lighting can be a significant investment in both initial cost and electricity usage, it pays to understand the options.

Safety Lights
When it comes to light pollution, safety lights are the biggest culprits. Many homeowners leave bright floodlights on continuously from dawn to dusk. A better option is to add a motion detector, so the light comes on only when it senses movement. Most fixtures allow you to adjust the sensitivity so the light is not tripped by swaying branches or blowing leaves. Most also allow you to set how long the light remains lit -- usually from five to 20 minutes.

Avoid "light trespass." If you've ever been annoyed by a neighbor's floodlight or a street light shining into your window, you know what this refers to. Most municipalities regulate commercial lighting, and some include homeowner lighting, to minimize disturbance to neighbors. This wayward light isn't just an annoyance, it's also a waste of electricity. Choose lights with "cut-off" or glare shields and adjust them so the light is directed downward, where you want it.

Task Lights
Task lighting illuminates specific areas. For example, you might install lights on your deck to illuminate patio furniture or over your barbeque so you can see the steaks you're grilling. When installing task lighting, make sure it's convenient to turn on and off so you'll use it only when necessary.

Accent Lights
Accent lighting lets you show off a sculpture, water feature, or certain plants. A popular option is "uplighting" -- installing lights at the base of a tree or object and directing light upward. Although dramatic and attractive, it can also contribute to light pollution. If you choose to use uplighting, use the lowest wattage bulbs possible. Think moonlight. Don't strive to turn night into day.

Types of Bulbs
Shopping for landscape lights can be overwhelming, especially when it comes to choosing the light source. Here are some options:

Incandescent light bulbs are inexpensive but the least efficient. Only about 5 to 10 percent of the energy consumed is converted to visible light; the remaining is lost as heat. Halogen lights are a type of incandescent bulb. They have a much longer life than regular incandescents but are just as inefficient and operate at high temperatures, increasing the potential fire hazard.

Fluorescent lights are much more efficient at converting energy to light. Compact fluorescent lights use about one quarter the energy that incandescent bulbs use to put out the same amount of light. The initial cost is higher but they last much longer.

In high intensity discharge (HID) bulbs, light is produced by passing a current through a metal vapor. They take several seconds to reach full lighting potential. They include mercury vapor, metal halide, and high-pressure sodium. Because they are very long-lasting, they are often used for difficult-to-reach lights and in commercial settings.

Low-voltage landscape lighting runs on 12 volts; although the bulbs are incandescent, they are low wattage and therefore save energy over higher wattage bulbs. Low-voltage systems provide plenty of light for paths.

Light-emitting diodes (LEDs) are relatively new to landscape lighting but hold great promise. They offer up to 90 percent efficiency -- compare that to the 5 percent efficiency of incandescents. Although they're relatively expensive now, prices will likely drop as they gain in popularity. The light from LEDs often appears bluish. Because they can be used with 12-volt power, LEDs may begin to replace low-voltage incandescent bulbs.

Solar lights are the most energy efficient of all, since they run off the power of sunlight. Small solar panels charge batteries in the fixtures that power the lights during hours of darkness. Most have an integrated photocell that turns lights on at dusk and off at dawn. Most solar lights aren't very bright but by spacing them relatively closely they'll provide adequate light for a walkway.

The International Dark-Sky Association estimates that 10 billion dollars in unnecessary lighting shines up into the sky in the United States alone. Generating the electricity needed to run those lights requires vast resources and contributes to greenhouse gases. Imagine if individuals and municipalities included light pollution in their conservation efforts. Perhaps if we all used light more effectively and conservatively, our children would know that the Milky Way is much, much more than a candy bar.

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