Lower color temperature lighting is not just for coasts

I get emails. Occasionally they reveal that things that I might have thought were obvious need to be explained. This past week it was an inquiry from an engaged advocate reporting that a local jurisdiction did not think that the advice from one of my papers on avoiding adverse effects on the environment by using lower color temperature lights applied to their situation in an inland forested area but was instead limited to coastal areas. Looking at the paper in question, “Rapid assessment of lamp spectrum to quantify ecological effects of light at night” (Longcore et al. 2018), I can sort of see where they were coming from. So let me clarify — the results apply across the board, not just to coastal areas.

In the paper we looked at responses of insects, sea turtles, shearwaters, and juvenile salmon. I can see how someone looking at the paper would think that with three groups associated with oceans for at least part of their lives the conclusions might only apply along coasts. But that conclusion would ignore that we also looked at insects, which was calculated from studies describing the relationship between spectrum and attraction for moths, bees, and all insects combined. To provide some extra background on this point, I pulled out and graphed these separate response calculations relative to CCT so the relationship between correlated color temperature and insect attraction is clear.

Calculated attractiveness of lights to bees (Menzel and Greggers 1985) , moths (Cleve 1964), all insects (Donners et al. 2018), and an average of these three groups as a function of correlated color temperature (CCT). Methodology and data in Longcore et al. (2018).

Insects are critically important in forests and avoiding impacts on them should be the goal of all natural resources managers. A significant role of light pollution in insect declines has been described (moths for example, Wilson et al. 2018) and the global decline of invertebrates should motivate any park manager who might be on the fence.

A second factor to consider is that the impacts on sky glow, which has behavioral impacts on species in all biomes, are reduced by lower color temperature lighting.

We also addressed spectrum in our 2017 report for the National Park Service, and concluded as follows:

Through all the considerations for different taxa, a few general lessons emerge to guide use of spectrum: 1) the choice of color significantly affects the degree of biological disruption; 2) narrow- spectrum lights are preferable to broad-spectrum sources (i.e., white light); 3) ultraviolet light should be avoided; 4) blue and shorter wavelengths increase biological responses and generally should be avoided; and 5) concerns about individual species in an area may influence the choice of least disruptive color for lights.

Longcore and Rich (2017)

These recommendations are not just for coastlines, but apply across biomes and especially in forests. One of the things to recognize from forests is that species that naturally live under the forest canopy are adapted to nighttime lighting conditions that are sometimes and order or two of magnitude dimmer than conditions in open habitats. Protection of the natural conditions for those species requires every tool in the lighting designers toolbox: good decisions when to light and not to light, appropriate shielding, limited intensity, reduced duration where possible, and well-chosen spectrum, for which the lowest CCT possible is a good rule of thumb.

Literature Cited

Cleve, K. (1964). Der Anflug der Schmetterlinge an künstliche Lichtquellen. Mitteilungen der Deutschen Entomologischen Gesellschaft 23:66-76.

Donners, M., van Grunsven, R. H. A., Groenendijk, D., van Langevelde, F., Bikker, J. W., Longcore, T., & Veenendaal, E. M. (2018). Colors of attraction: modeling insect flight to light behavior. Journal of Experimental Zoology A 329:434-440.

Longcore, T., and C. Rich. 2017. Artificial Night Lighting and Protected Lands: Ecological Effects and Management Approaches (Revised August 2017). Natural Resource Report NPS/NRSS/NSNS/NRR—2017/1493. National Park Service, Fort Collins, Colorado.

Longcore, T., A. Rodríguez, B. Witherington, J. F. Penniman, L. Herf, and M. Herf. 2018. Rapid assessment of lamp spectrum to quantify ecological effects of light at night. Journal of Experimental Zoology A 329:511-521.

Menzel, R., & Greggers, U. (1985). Natural phototaxis and its relationship to colour vision in honeybees. Journal of Comparative Physiology A 157:311–321.

Wilson, J.F., Baker, D., Cheney, J., Cook, M., Ellis, M., Freestone, R., Gardner, D., Geen, G., Hemming, R., Hodgers, D. and Howarth, S., 2018. A role for artificial night-time lighting in long-term changes in populations of 100 widespread macro-moths in UK and Ireland: a citizen-science study. Journal of Insect Conservation 22(2):189-196.

Not your usual correction

Colleagues Scott Loss, Tom Will, Pete Marra and I published an article a month or so in Biological Invasions, titled “Responding to misinformation and criticisms regarding United States cat predation estimates.” The purpose of the article was to address the spurious criticisms that have been leveled against estimates of predation by free-roaming cats published by Loss et al. in 2013.  A few days ago a correction was issued to the paper.  It was not something wrong with the paper but a “correction” is how the journal makes a previously published paper Open Access.  Now that it is OA, the downloads have passed 5,500.

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This paper is open access now.  Click to download.

New paper: underpass use by wildlife

New paper: underpass use by wildlife

Longcore, T., L. Almaleh, B. Chetty, K. Francis, R. Freidin, C.-S. Huang, B Pickett, D. Schreck, B. Scruggs, E. Shulman, A. Swauger, A. Tashnek, M. Wright, and E. E. Boydston. 2018. Wildlife corridor use and environmental impact assessment: a southern California case study. Cities and the Environment11(1):art4.


Environmental planners often rely on transportation structures (i.e., underpasses, bridges) to provide connectivity for animals across developed landscapes. Environmental assessments of predicted environmental impacts from proposed developments often rely on literature reviews or other indirect measures to establish the importance of wildlife crossings. Literature-based evaluations of wildlife crossings may not be accurate, and result in under-estimation of impacts or establishment of inappropriate mitigation measures. To investigate the adequacy of literature-based evaluations, we monitored wildlife use of a freeway underpass that had been identified as critically important to wildlife connectivity, and which was evaluated in an environmental review document. Photographs were obtained from a network of trail cameras over 3 years. Six mid- to large-sized native mammal species used the underpass and two other mammal species were photographed near the underpass but not using it. American badger (Taxidea taxus) was photographed at a higher rate in the underpass than in the surrounding area. Gray fox (Urocyon cinereoargenteus) was rarely detected in the underpass relative to surrounding habitats, whereas the absence of mule deer (Odocoileus hemionus) in the underpass was unexpected, given relatively frequent detection in adjacent habitats. These results differed from the environmental assessment in that American badger was listed as “potentially” present while mule deer were expected to use the underpass. Results underscore importance of gathering data to document wildlife use of corridors, because some species do not or rarely take advantage of apparently suitable corridors, while others may be present when assumed to be absent.

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New paper: picking spectrum to reduce adverse effects of lights on wildlife

New paper: picking spectrum to reduce adverse effects of lights on wildlife

Back during the Ecological Consequences of Artificial Night Lighting conference in 2002, the prescient Steven Pauley made a strong argument that blue light should be avoided in outdoor lighting for human health reasons and posed the question whether it would reduce impacts on wildlife too.  My position at the time was, based on the research presented during the conference, a “silver bullet” for spectrum was not yet known.  For example, we had instances of yellow light being best to minimize insect attraction while some salamanders mis-oriented under yellow light.  Certainly the skyglow reasons to avoid blue light were known, but what color would be best for species?

The LED revolution has made this question even more important and with a new paper this week, we have proposed an analytical framework to address the question and provided an analysis of spectrum for a range of existing outdoor lighting products.

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Our new paper, part of a special issue on light pollution and its effects edited by Davide Dominoni and Randy Nelson.

It turns out that overall, Dr. Pauley is right.  We should be avoiding blue light for the sake of wildlife, at least for those wildlife species where we have good spectral response curves.  And when you combine wildlife with melatonin suppression and sky glow, the use of 3000-5000 K LEDs looks like a bad idea.

We looked at insect responses, sea turtle response, a response curve for Newell’s Shearwater, and a response curve for juvenile salmon (all previously or concurrently published).  Then we converted the spectral power distributions of a range of existing light sources to quantal flux and intersected them with the response curves.  Low Pressure Sodium turns out to be the most wildlife-friendly lamp, in addition to being the favorite for reducing astronomical impacts.  But LPS will not be manufactured much longer, so among the LEDs, PC Amber and filtered yellow/green LEDs intersected the least with the wildlife responses.

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Figure 3 from Longcore, T. et al. (2018) Rapid assessment of lamp spectrum to quantify ecological effects of light at night. Journal of Experimental Zoology A. DOI: 10.1002/jez.2184

These patterns are predicted by Correlated Color Temperature (CCT) sufficiently so that one could use it as a rule of thumb.  Some outliers, like the spectral output of kerosene oil, which has a low CCT but high wildlife impacts, reduce the power of the association.  Some animal groups have higher correlation with CCT than others.  Overall the r² is 0.62, and for insects it is 0.82.  But for sea turtles and Newell’s Shearwaters it is lower.


Relation between Correlated Color Temperature and intersection with sensitivity of wildlife groups.  Higher wildlife scores predict higher effects on the group that would be desirable to avoid.  Data from Longcore et al. (2018).

As we show in the paper, it is possible to have relatively low intersection with sensitive areas of the spectrum for a combination of wildlife, circadian rhythms, and sky glow, while still providing reasonable color rendering for human vision.  If we wanted to minimize impacts from outdoor lighting, LPS is still the best product.  But one of the reasons it has not been widely deployed is the complete lack of color rendering.  What we found is that new LED products that mostly if not entirely avoid the blue end of the spectrum present an opportunity to reduce impacts of outdoor lighting. To do so, however, will take more than switching to 3000 or 2700 K LEDs, products below 2200 K CCT that look more yellow than white are the way to go.  It still isn’t a silver bullet, and a spectral mitigation strategy has to be coupled with directionality and dimming, but we think the results provide a replicable approach to support the use of PC Amber and filtered LEDs for outdoor lighting.

Wait, there’s more.  All of the lamp spectra, spectral response curves, and summary assessments are available on github, with a webpage deployment of the code here: https://fluxometer.com/ecological/ . You can download and insert your own animal response curves or lamp spectral power distributions.  Please, if you have a behavioral response curve for a species or group of species, send it to us and we’ll add it to the webpage.

Finally, here are a couple of graphs that could be used in presentations, showing the relationship between CCT and the wildlife index.



Unintended Outcome? Required Solar Panels on New Houses Limits Future Urban Forest

Unintended Outcome? Required Solar Panels on New Houses Limits Future Urban Forest

At today’s meeting of the California Energy Commission, an update to the California Building Energy Efficiency Standards was passed that would require solar panels on the roof of all new residential construction.  In the abstract, I am a strong supporter of distributed solar generation, especially as a means to reduce impacts to wildlands from extensive solar arrays and distribution systems.  The update was passed through on a Negative Declaration, with no adverse impacts to the environment anticipated.

Required solar photovoltaic panels on all new construction, however, will dramatically impact the ability of developers of and neighbors to new housing to plant and maintain trees for shade and their other benefits.  California has a solar shade law, the Solar Shade Control Act, which prohibits planting of trees and shrubs that would shade more than 10% of an active or passive solar collector between 10 a.m. and 2 p.m.

The net result of these two regulations is that the number, type, and location of trees that can be planted in new housing developments will be dramatically constrained, and those living next to new construction will be constrained from planting trees for beneficial shade if they might eventually shade the solar panels next door. I don’t think the Energy Commission thought about this, or at least they didn’t include it in their environmental review. The conflict between urban forest benefits and the solar shade law has implications for stormwater management because trees reduce peak flows and help to improve stormwater quality.

Obviously there is a tradeoff between access to the sun for solar power and the benefits of a healthy urban forest.  The ability to have both an urban forest and distributed solar generation depends on planners, urban designers, and regulators working out the tradeoffs ahead of time — figuring out the lost benefits from shade trees (to biodiversity, local temperature and cooling costs, stormwater quality and quality) relative to the energy savings from solar panels not being shaded.

Let me know what you think. Have I missed something?

Travis Longcore, Ph.D.
May 9, 2018

(Award-winning) Light Pollution Research at USC Undergraduate Symposium

(Award-winning) Light Pollution Research at USC Undergraduate Symposium

We participated in force in the 20th University of Southern California Undergraduate Symposium for Scholarly and Creative Work. Our contributions included:

  1. Classification System for National Park Sites Based on Nightscape Lighting Profiles (Harrison Knapp and Benjamin Banet)
  2. Spatiotemporal Analysis of Lighted Boats at Night (Eliza Gutierrez-Dewar)
  3. A Photographic Light Pollution Assessment Across Western Public Lands (Benjamin Banet)
  4. Characterization of Spatial and Spectral Distribution of Outdoor Lighting at Wrigley Marine Science Center (Camille Verendia, Lisa Cortright, and Jasper McEvoy)

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    Amanda Gilmore, who worked this semester on habitat modeling for invasive lionfish, presented her ongoing work with our colleague Dr. An-Min Wu.

    Awards were won. Eliza took the 2nd Place award in physical sciences for her work analyzing squid boat lights off the coast of California, while Ben won Honorable Mention for his field work documenting light pollution on public lands across much of the American West with hemispherical photography.


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    Acknowledgments are in order. Funding from the Undergraduate Research Associates Program, Summer Undergraduate Research Fellowship, and Student Opportunities for Undergraduate Research (all at USC) made this work possible.  We also had funding from the National Park Service via the Southern California Research Learning Center for part of Ben’s work (the part in the Santa Monica Mountains National Recreation Area and Channel Islands National Park).  Eliza’s work was made possible by collaboration with Chris Elvidge at NOAA, who provided the outputs of their boat detection algorithm. The Wrigley Institute and Wrigley Marine Science Center supported the lighting assessment there with travel, room, and board. Photos from the symposium and awards dinner are by Susan Kamei; I was at the AAG annual meeting.

Lab Work in Knowable Magazine Profile

Screen Shot 2018-03-26 at 9.38.02 PM.pngReporter Stephanie Pain contributed an excellent summary of recent research on light pollution, “There Goes the Night,” with interviews and summaries of research from around the world.  Knowable Magazine is the partner publication to the Annual Reviews series, which recently published a review from the Gaston lab, Impacts of Artificial Light at Night on Biological Timings.  Our favorite part, however, is that the article included an image from Ben Banet, who graduates this spring with an interdisciplinary B.S. in conservation and GIS that focused on light pollution.  His image of the Smithsonian research hut on Mt. Whitney with the glow of Los Angeles on the horizon 285 km in the distance provided a striking illustration for the article.

Two light pollution research updates

I’m usually one to announce research results and not grant funding, but the funders put out a release and Tweet, so it is officially news that we are starting a new 2-year project: Coast Light: Actionable Science to Manage Coastal Nightscapes. The funding is from USC Sea Grant and includes in-kind contributions from many partners that will make the project possible — including data, labor, and/or time from Los Angeles County Museum of Natural History (collaborating on measuring influence of light on settlement rates of marine invertebrates), The Aerospace Corporation (providing coastal night light measurements by cubesat!), Los Angeles Audubon Society and the many volunteer snowy plover monitors, and Professor Karen Martin at Pepperdine (grunion data).  More about the project as it develops — I’ll be co-advising a Ph.D. student from Biological Sciences who will be the official Sea Grant Trainee on the project.


Preliminary results from analysis of radiance-weighted nighttime boat detections by month off the coast of southern California (Gutierrez-Dewar, Elvidge, and Longcore, unpublished data).

Our Park Light research efforts are coming to an interim head, as at least three lab members will present at the Los Angeles Geospatial Summit on February 23.  Harrison Knapp and Ben Banet will present a classification of National Park Service units based on the lighting conditions inside the parks and in buffers surrounding them, so that parks can know what other parks face similar issues for light pollution management.  Eliza Gutierrez-Dewar has some very interesting results looking at the spatial and temporal distribution of squid boats off the Pacific Coast, which can be identified using night lights because of the bright lights used by squid fishers to attract the squid up near the surface where they can be caught.  This project builds on data produced by an automated boat detection algorithm developed by Chris Elvidge’s group at NOAA and is of significant interest to land managers looking to protect sensitive seabird nesting sites from excessive light (and associated predation risk) during nesting season. We may have another poster, but I have not reviewed the final program yet.

Drivers of plant community structure on San Clemente Island

Drivers of plant community structure on San Clemente Island

A third paper from our collaboration with Scott Loss and post-doc Shishir Paudel at Oklahoma State University has been published in Ecosphere.  This paper analyzes the vegetation data collected as Shishir searched for invasive earthworms on the island.

Determinants of native and non-native plant community structure on an oceanic island

Shishir Paudel, Juan C. Benavides, Beau MacDonald, Travis Longcore, Gail W. T. Wilson, and Scott R. Loss

Understanding the relative importance of environmental and anthropogenic factors in driving plant community structure, including relative dominance of native and non-native species, helps predict community responses to biological invasions. To assess factors influencing plant communities on San Clemente Island, USA, we conducted an islandwide vegetation survey in which we measured plant species richness and percent cover of native and non-native plants, as well as physical environmental variables, soil chemical properties, abundance of soil microbial functional groups (e.g., arbuscular mycorrhizal fungi [AMF]), and a human disturbance variable (distance to road). We found that total plant species richness decreased with increasing non-native plant cover, soil pH, and AMF abundance. Native plant cover increased with increasing distance to a major paved road and decreased with increasing soil moisture and pH. Non-native plant cover decreased with increasing distance to a major paved road and increased with increasing soil moisture, AMF abundance, and from southwest to northeast, a geographic/climatic gradient that represents increasing moisture. Nonmetric multidimensional scaling ordination further illustrated that trends in plant community composition were correlated with elevation, distance to a major paved road, and soil moisture, organic matter, and ammonium. These results suggest complex effects of physical environmental, soil chemical, and human-related factors on plant community structure on an oceanic island, and moreover, that different factors affect cover of native and non-native plants. Notably, our observation of apparent moisture limitation of non-native plants suggests that, in some contexts, drought conditions can limit plant invasions and may even represent an opportunity for efficient control or eradication of invasive plants. The apparent negative effect of non-native plants on native plant cover and overall plant species richness represents a conservation concern for native biodiversity on oceanic islands and suggests the potential for community reassembly as invasive species increasingly dominate due to anthropogenic disturbances.

Paudel, S., J. C. Benavides, B. MacDonald, T. Longcore, G. W. T. Wilson, and S. R. Loss. 2017. Determinants of native and non-native plant community structure on an oceanic island. Ecosphere 8(9):e01927. 10.1002/ecs2.1927