Preserving Darkness for Moths and Other Denizens of the Night

Guest post By Leora Radetsky – Senior Lighting Scientist and LUNA Program Director for the DesignLights

Studies documenting declines in wildlife species aren’t new or unique, but some findings stand out, sending a ripple of unease across the conservation community. Such was the case five years ago, when the journal Biological Conservation reported the results of a study revealing huge rates of decline in insects across the globe. The authors concluded that over 40 percent of insect species are threatened with extinction and cited Lepidoptera – the taxa comprising moths and butterflies – as among the most affected. Many human activities are linked to insect declines, from toxic agrochemicals and habitat loss to invasive species and climate change. Electric lighting, another human innovation, is also linked to the decline of nocturnal insects like moths. The past several years have yielded numerous studies investigating the impacts of nighttime electric lighting on insect behavior.

While the overall results don’t point to nighttime lighting as the primary reason for decreasing moth numbers, they do raise concern. A 2017 study published in Biology Letters, for example, found that electric nighttime lighting, using green, white or red light, inhibits feeding behavior in moths, “providing evidence for sublethal effects contributing to moth population declines.” A comprehensive review conducted in 2020 in Insect Conservation and Diversity examined the life cycle impacts of artificial light at night (ALAN) and found “evidence of diverse impacts across most life stages and key behaviors” and cited “growing concern that light pollution may have a role in moth declines”.

The most recent research on moths and ALAN provides new understanding of moths and their positive movement towards light (phototaxis). Upending age-old assumptions about why outdoor lights are routinely mobbed by moths (and other flying insects), a January 2024 paper in Nature Communications found that nocturnal flying insects actually aren’t visually attracted toward light fixtures “like moths to a flame.” Instead, flying insects are hard-wired to turn their backs toward the brightest light source. Under natural conditions such as a forest, the brightest light source is the sky and their instincts ensure proper orientation needed to maintain correct flight position and control.

“Near artificial sources, however, this…dorsal light response can produce continuous steering around the light and trap an insect,” the authors wrote, adding that even if they could right themselves once away from the light source, they returned to the light source and “consistently directed their dorsal axis toward the light source, even if this prevented sustained flight and led to a crash.” They noted that “understanding how insects interact with artificial light is particularly important amid modern increases in light pollution that are a growing contributor to insect declines.”

For humans who care about the environment, this presents a conundrum. Since the first electric streetlights in the late 1800s, outdoor lighting has enabled myriad human activities, from navigation and work to sports and celebration. Today, outdoor light at night is so pervasive and essential to our 24/7 culture that most people go about their after-dark pursuits without giving it a second thought.

With research showing that light pollution is increasing in North America at a rate of approximately 10 percent per year, however, there is growing awareness of the need to balance society’s reliance on quality outdoor lighting with the important function darkness plays in the lives of all living things.

Fortunately, light pollution is a challenge that can be solved instantly with readily available solutions. By following these seven basic strategies, commercial facility operators, municipal building managers, colleges and universities, and others can help mitigate the unintended consequences of light pollution. These strategies include:

• Use outdoor lighting that is dimmable and compatible with networked lighting controls, which can switch and dim lights individually and remotely.
• Consult with local experts and residents to identify and address any specific local concerns regarding wildlife and equity impacts.
• Use only the right amount of light; avoid over lighting above the recommended light levels prescribed by local authorities or using recommendations from the Illuminating Engineering Society (IES).
• Use lighting controls to reduce energy use and light pollution on a nightly basis after closing time or when spaces are unoccupied through dimming and timed usage.
• Control lighting to respond to seasonal changes in the environment. (Dim and switch off non-essential lighting for unoccupied spaces during the adult moth emergence season, for example).
• Control the distribution of light. (Select lights that only produce light in the downward direction, or have additional shielding to block light from going where it is wasted, and avoid aiming lighting towards the horizon or sky.)
• Minimize use of blue-violet light which scatters into the atmosphere more easily than does “warmer” white light or red-amber light. (Choose products with correlated color temperatures (CCT) at or below 3000 Kelvin.)
  

In the commercial sector, it’s possible to check several of these boxes at once by choosing products on the DesignLights Consortium’s (DLC) LUNA qualified products list (QPL) and installing these fixtures following the best practices for responsible light at night. The DLC is a non-profit that provides decision makers with data and resources on quality lighting, controls and integrated building systems to reduce energy use, carbon emissions and light pollution. Products that satisfy our LUNA technical requirements also meet the criteria for most North America commercial lighting energy efficiency programs – making them eligible for money-saving rebates and incentives.

LUNA-qualified products help mitigate light pollution by 1) reducing sky glow by requiring that fixtures meet uplight, aiming, dimming and correlated color temperature (CCT) thresholds; and 2) reducing light trespass through product shield requirements.

Leora Radetsky is Senior Lighting Scientist and LUNA Program Director for the DesignLights Consortium.

DLC is a 2024 National Moth Week supporter. The NMW is thankful for the support.