Studying the Ecological Impact of LED Street Lights

Bright lights big city: do energy-efficient LED lights cause unexpected ecological damage?

PLoS Blogs, March 24, 2016. Image credit: InSapphoWeTrust

Planet earth runs on light energy.  Light energy from the sun powers photosynthetic processes in plants and different wavelengths of light cue these plants to flower, move their leaves, and grow taller.  These same cues influence animals as well.  Insects are attracted to narrow range UV lights, based on the evolved sensitivities to UV light in their eyes.  Some birds are adapted to only sing mating calls at nightbased on the light quality from a full moon.  High light levels can increase the mating behaviors of some frogs and changes in the quality of light can affect bird nesting behaviors.  With so much of the natural world dictated by fine-tuned associations with light quantity and quality, how does the constant light pollution of cities affect the behavior of these organisms?  Can different types of light pollution (street lights, billboards, or cars) affect ecological interactions in different ways?  And can we design cities to interfere less with these naturally evolved relationships?  Can different types of light pollution affect ecological interactions in different ways? Click To Tweet

Many cities worldwide have begun to shift towards LED light bulbs in streetlights due to improved color rendering (broader spectrum light quality) and increased energy efficiency over time.  In fact, the United States Department of Energy reports that residential LED’s can reduce energy use by 75% and last 25 times longer than traditional incandescent lighting.  In places like New York City, these changes are projected to result in up to $14 million annually (energy savings and maintenance) and are a huge step towards to city’s goal of reducing carbon emissions 30% by 2030.

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The authors studied bat behavior (bat calls and feeding behavior) before and after streetlight replacements with LED bulbs.  Bats are usually attracted to these streetlights due to some combination of (1) the high abundance of food (insects) attracted to these light environments and (2) the ability of some bats, such as vesper bats, to see the UV light emitted from some types of bulbs (e.g. metal halide).  The authors suggest that in this comparison between LPS and LED bulbs there is little change in light quantity in the UV range.  LPS emits light in a much narrower range, but the cool LED’s used in the studied municipalities do not emit in the UV range at all, and the neutral LED’s emit at a very low level.  This may mean that in our design of more sustainable cities, the switch to LED’s may be a reasonable choice for both energy efficiency and bat behavior.

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