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.