How Light Pollution Affects Life in the Garden

Artificial light at night disrupts natural cycles, harming plants and animals. Use these tips to learn how you can reduce light pollution to help birds, bats, fireflies, and more.

Moths are also affected by light pollution. This explains why it’s helpful to regard moths as butterflies on night shift.

The Problem With Light Pollution

You’ve probably heard about recent initiatives in big cities to get office skyscraper lights turned off at night during key bird migration periods.

Many birds migrate at night, and when lights are glowing high up on these buildings—right along flight paths—birds can become disorientated, smashing right into the glass windows, and falling to their deaths. The number of bird fatalities from this type of light pollution is staggering.

Another example is fireflies (lightning bugs). Those flashes of light they emit are part of their mating rituals—but only in the dark of night, not with artificial lights present.

We see moths flying frantically around patio lights and that’s not a good sign either. They are not actually “attracted” per se but instead lose their orientation, unable to fly away.

And that’s just a few examples.

With half of all species active at night, this is a big problem—a problem that has been increasing for decades.

You’ve probably seen satellite images showing how much brighter the Earth is at night now compared to years past.

More of us are living in urban areas, and, in turn, urban areas are spreading out, and with that goes the spread of lights at night.

There are, of course, valid safety reasons to have outdoor lights at night. But a lot of lights are also just used for decoration or ambiance—and that’s where we can help.

You can jump to the practical tips here or keep reading for more details.

The Need For Both Day & Night

“It is estimated that half of all species on Earth start their “daily” activities at sundown.”

International Dark-Sky Association

Because LED lights require much less energy, it is now more affordable to increase lighting and leave them on for longer periods.

At first glance that might seem okay for our plants, animals, and trees. They convert light energy into chemical energy. That’s their fuel.

So, what’s the problem with a longer period for photosynthesis?

Plants have evolved under certain lighting conditions, including daily cycles of day and night, and night is an important part of that.

Also, predictable annual patterns of days getting longer in the spring and then shorter in the fall—in most parts of the world—play an important role as well.

Plants do use light for energy, but they also use light for information, and night lighting and unnatural light cycles can give them some bad information.

Along with photosynthesis (where sunlight is converted into carbohydrates for plant growth), plants also use light for phototropism—the way plants will move toward or away from light—and photoperiodism, which is how they respond to different lengths of day and night.

Artificial lights can mess all of this up.

Related

• A refresher on the role of light and photosynthesis for gardeners.
• Sunflowers and heliotropic movement (where they face light during early growth stages)

Examples of Light Disruptions

When artificial lights are present at night:

• Plants that bloom in the fall may never bloom or can bloom at the wrong time because they never experience the shortening of the days in the fall.
• Trees (think of trees right below streetlights) may keep leaves green that under natural conditions would change colors and fall.
  Shedding leaves is an important part of a tree’s survival preparations for the winter: lights can interfere with that.

And it’s not just the plants themselves.

Night lighting can also have an impact on pollinators and other insects and animals that feed on plants.

• Birds exposed to artificial lights can become distressed and lose sleep; they may wake earlier in the day and lay their eggs earlier in the season too far ahead of available food for their young. Artificial lights also interfere with their (nocturnal) ability to hunt at night.
• Bats can miss prime time for eating insects when lights artificially extend dusk.
• Sea Turtles cannot find their way to the ocean when artificial lights are present.

We’ve all discussed how lights can completely distract moths while they fly obsessively against them and eventually die. This explains more on why moths are an important part of nature.

Blue and white lights are particularly disruptive to sea life including fish, frogs, and turtles.

I’ve noticed something similar in my own garden. If an outdoor light is turned on at night, frogs and toads stop their mating calls and often do not resume for hours. It’s anecdotal but no less concerning. This has more tips on creating safe habitat for frogs.

The lists go on and on. With so many animal species active at night, there are thousands of examples. I’d suggest diving into the research if you want to learn more and join others who are working to reduce this problem.

So yes, the entire ecosystem can be affected by bright night-time lighting. The long-term consequences are not yet clear but it’s not looking good.

How to Help

While dimly glowing garden lights are likely not adding significantly to the problem (compared to the mass of other lights used at night), light pollution is an issue.

Do an audit of your outdoor space and see if you can reduce some lighting without foregoing safety.

Tips To Reduce Light Pollution

Outdoors

• If outdoor lights are purely cosmetic, keep them off.
• If you just need them at certain times, use timers or motion sensor lights.
• Choose low-impact lights.
  • Use “warm” light colors, not “blue” lights.
  • The color temperature of the bulbs should be below 3000 Kelvins.
  • Narrow-spectrum amber LEDs are a good option.
  • IDA dark sky certified light fixtures shine down, not up.
• If light bulb cannot be changed, install light shields (red gel filters) to reduce the impact.

Indoors

• Keep curtains or blinds closed when lights are on indoors at night.

Community

• Participate in Lights Out initiatives where whole communities block out night light to clear the way for bird migrations.
• Find out whether your town or city has a lighting code (or needs one). The International Dark Sky Association has lots of helpful tips and resources.

Resources

Listen

Book

• Fireflies, Glow-worms, and Lightning Bugs: Identification and Natural History by Lynn Frierson Faust

Read More

1. Putting animals in their best light: Some shades of LED lamps threaten wildlife
   A research team identifies harmful effects to wildlife as LED lights proliferate. Some hues, including blues and whites, imperil creatures while other wavelengths are more benign. They devised an interactive web-based tool to help people make wildlife-friendly choices in outdoor lighting.
2. Light pollution shown to affect plant growth, food webs
   Artificial nighttime light from sources such as streetlamps affects the growth and flowering of plants and even the number of insects that depend on those plants for food, a study confirms.
3. Ecological effects of artificial light at night on wild plants
   In many cases, artificial light in the night‐time environment is sufficiently bright to induce a physiological response in plants, affecting their phenology, growth form and resource allocation. The physiology, behaviour and ecology of herbivores and pollinators are also likely to be impacted by artificial light.
4. Insects and Street Lights
   Artificial lighting is ubiquitous in the developed world – but the effects of nighttime illumination on wildlife are not yet fully understood. While we know that artificial light changes the behavior of some animals we’re still a long way from knowing whether those changes can damage wildlife populations.
5. Fireflies need dark nights for their summer light shows – here’s how you can help
6. While Fireflies Await a Night That Never comes | A study found that while some fireflies shrugged off light pollution, members of other species failed to mate even when males and females could find each other | New York Times
7. Why are insects drawn to light? | New York Times
8. International Dark-Sky Association | Helpful information to support this cause.

~Melissa the Empress of Dirt ♛