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Let there be light — but be mindful of the wildlife

  • Artificial lights affect biological processes, such as plant photosynthesis, animals’ orientation and migrations, and human circadian rhythms. As communities replace older lights with energy-efficient light-emitting diode (LED) lamps, they must weigh the needs of people with damage to local wildlife.
  • Researchers have developed an tool that categorizes LED lamps by their output, energy efficiency and predicted impacts on wildlife, people and the darkness of the night sky.
  • The researchers predict that filtered yellow-green and amber LEDs should have lower effects on wildlife than high-pressure sodium lamps, and that blue-toned light will affect wildlife — including birds, insects, fish, and sea turtles — more than orange- and yellow-toned light.
  • Their results are presented on an updatable website to guide lighting designers and local government officials in installing lighting technologies that are both energy-efficient and less likely to harm wildlife.

Lighten up

We’ve all seen insects fly toward light. Moths, for example, use moonlight to stay upright, fly straight, and remain oriented at night.

Other groups of animals, including various species of birds and fish, also use the cues of natural light to guide their movements. Hatching sea turtles leave their nest in the sand and walk away from dark elevated silhouettes toward the light of the moon’s reflection on the ocean.

Different species respond to light at different portions of the electromagnetic spectrum. Moths and sea turtles, for example, are attracted by light at shorter wavelengths (blue, violet, ultraviolet tones) more than longer wavelengths (yellow, orange, red tones), while salmon are sensitive to light at various wavelengths.

Hundreds of thousands of mayflies, winged aquatic insects in the order Ephemeroptera, attracted to the lights on a bridge over Spain’s Rio Ebro. Sensitivity to reflected light that can indicate water, mayflies can be fooled and then trapped by artificial lights. Image by Oiluj Samall Zeid, (CC BY 2.0), via Flickr

Artificial light can affect biological processes, such as plant photosynthesis and animal orientation and migration. Introducing artificial light to beaches, oceans, forests, or rivers at night can attract or disorient animals, steering them off course and ultimately killing them. Various fish species will swim away from artificial light. Migratory birds use light from the blue-green part of the spectrum for magnetic compass orientation, and longer-wavelength red and white light interferes with that orientation.

An array of LED choices

The rapid increase in the use of lower-cost, energy-efficient light-emitting diode (LED) lamps globally prompted a multi-institutional research team to develop and publish an assessment of the impacts of current LED lamp options on sensitive wildlife, together with methods to predict the effects of lamps on several species with different spectral profiles without having to conduct field studies.

Initially emitting primarily whiter or bluer light, LED lamps are now available in a wider range of spectral and color options that communities can use for outdoor lighting. LED producers are working to create lights that are less damaging to wildlife than those currently available, lead author Travis Longcore, an urban ecologist at the University of Southern California, told Mongabay-Wildtech.

Longcore and his colleagues measured the light emitted by 26 LED lighting products of varying materials and spectral outputs, including PC Amber lights and filtered LEDs.

A warm white LED lamp attracts insects to a pan trap as part of an experiment investigating the effect of spectrum on insect attraction. Image by Travis Longcore

They consulted published data to estimate the expected relative responses of species known to be sensitive to light — including several sea turtle, insect, and salmon species, as well as plants, through photosynthesis — to a range of lamp types and light of various wavelengths.

To understand the trade-offs between minimizing effects on different taxa and optimizing the performance of each lamp for outdoor lighting, the researchers also measured several criteria important for a product’s visual performance and energy output. These included two measures of light color—the correlated color temperature (CCT), a gradient ranging from “warm” reds to “cool” blues, and its color rendering index (CRI), how faithfully an artificial light source reveals colors compared to natural light.

By comparing the lamp spectral outputs (including the CCT and CRI values) to the known visual characteristics and behavioral responses to light of the various wild species, the research team developed a model to predict species’ responses to LED lamps of different spectral output, assuming equal light intensity. The model predicts the impact on individual animal groups and on wildlife overall, identifying lamps that minimize predicted ecological, physiological, and astronomical effects.

A hatchling loggerhead sea turtle in Florida, USA, moves away from the sea and toward high-pressure sodium roadway lighting. Image by Blair Witherington

The team measured the species’ responses to light in units that are compatible with international standards to enable others to use and test the model and to compare the impacts on wildlife of new lighting products.

Warmer-toned light may reduce impact on wildlife

The researchers found that lamps of certain materials and spectral outputs affect wildlife more per unit of energy emitted than others. Adding more lighting power to lamps with orange and yellow tones affected wildlife less than those with bluer tones.

“Using these assessment metrics,” the authors state in their paper, “filtered yellow‐green and amber LEDs are predicted to have lower effects on wildlife than high-pressure sodium lamps, while blue‐rich lighting [e.g., CCT value greater than 2,200] would have greater effects.”

Additionally, some species respond more to various light spectra than others. “A high proportion of the power from all lamp types is calculated to influence loggerhead [turtle] hatchlings,” the authors found, “while few lamps concentrate their power in the areas of the spectrum most attractive to juvenile salmon.”

The model can be updated to include response curves of additional species or information on additional types of lamps.

The authors acknowledge the need for more research on species’ responses to light to improve the accuracy of their predictions, as the responses even among populations of the same species may vary.

“Our contribution is to say: We need this. Here’s how to do it, and the technical steps and the language and the first results,” Longcore told Anthropocene magazine. “You can download what we did, add your own curves and species and lamps, or share them back with us.”

An appeal for wildlife-friendly outdoor lighting

The project aims to provide information to lighting designers, government agencies, and regulators responsible for switching to high-efficiency outdoor lighting such as LEDs to build and use new lighting technologies that are less likely to harm wildlife.

A grounded Cory’s Shearwater that was attracted to the city lights of Tenerife, Canary Islands. Lights from towns, fishing boats, and oil rigs can disorient night-flying seabirds, causing them to land. Grounded seabirds are vulnerable to land-based hazards such as predation, collisions, and starvation. Image by Beneharo Rodríguez

“The overall message is that cities should look to use the lowest possible color temperature for outdoor lighting, including lights that do not appear white, but rather yellow and green,” said Longcore. “Also, for areas with specific ecological concerns, our approach should support a decision to use lights that are best suited to those particular concerns (e.g., reducing insect attraction, turtle attraction).”

The authors say that installing lamps that cause minimum wildlife impact per amount of usable light offers a compromise between human light preference and support for local nature. The brightness of light is also known to affect species’ vision and behavior, so communities can further reduce harm to wildlife by controlling the intensity, direction, and duration of outdoor lighting.

“No light on a sea turtle nesting beach, on a penguin colony, or on the route a fledgling seabird takes to the sea would be optimal,” they state, “but if there is to be a light nearby, minimizing the wavelengths in the part of the spectrum to which turtles or seabirds are most sensitive is preferable, so long as intensity is also minimized.”

A pair of washed-back baby sea turtles being returned to the sea. Hatching sea turtles face myriad hazards, including storms, predators, and, more recently, artificial lights. Image by Andrea Westmoreland, (CC BY 2.0), via Wikimedia Commons

Citation

Longcore, T., Rodríguez, A., Witherington, B., Penniman, J. F., Herf, L., & Herf, M. (2018). Rapid assessment of lamp spectrum to quantify ecological effects of light at night. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology.

The researchers have placed the results of their assessment on a website and their data and Java script on GitHub.

 

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