How Light Pollution Affects Life in the Garden

While we do not know the long-term effects, it is clear that light pollution is disruptive to the life cycles of plants and animals. Whether it’s animals like fireflies, birds, moths, or bats, or plants and trees, living things need both times of darkness and light.

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How Artificial Lights Affect Plants and Animals

I first started thinking about this topic after reading about how fireflies, glow-worms, and lightning bugs light up (for various survival purposes) and how artificial lights can interfere with this.

And that got me wondering about the effects on other insects, birds, amphibians, mammals and plants.

So, how do artificial lights affect life in the garden?

For many decades we have seen increasing levels of light at night.

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.

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

There are, of course, valid safety reasons to have outdoor lights at night but, as you read this, consider whether you’ve got decorative lights on at night that could be decreased or kept off entirely to help decrease the light pollution interfering with nature.

I’ve listed tips for reducing light pollution at home here.

Increased Light Exposure

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.

This has more information on the role of light and photosynthesis in your garden.

Sunflowers have heliotropic movement as described here.

Examples of Light Disruptions

With outdoor artificial lighting 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 street lights) 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 on other insects and animals that feed off the 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.
• Bats can miss prime time for eating insects when lights artificially extend dusk.

We’ve all seen how lights can completely distract moths while they fly obsessively against them and eventually die.

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

I know that if I turn on a light in my garden at night and the frogs and toads stop their mating calls and may not resume for hours.

The lists go on and on. I’d suggest diving into the research if you want more examples. There are countless examples and it’s really alarming.

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.

Let Darkness Be

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 to be aware of.

And, if you need some encouragement, keep in mind that slugs are attracted to lights at night and those patio lights may be encouraging them. I’m partly kidding but you get the idea—both light and darkness have profound effects on living things.

It’s worth doing a light audit of your garden at night. I’ve listed some tips below to help.

Resources

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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 night time light from sources such as street lamps 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 night time 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

~Melissa the Empress of Dirt ♛