April 3 2024
To: Palo Alto Architectural Review Board
By email to: arb@CityofPaloAlto.org
CC: claire.raybould@cityofpaloalto.org
Re: Lighting at 2501 Embarcadero Way - Local Advanced Water Purification System
Dear Chair Baltay and commissioners,
The Santa Clara Valley Audubon Society and the Sierra Club Loma Prieta Chapter are organizations united by our shared commitment to the protection of the environment, nature, and open space, and we represent thousands of members in the City of Palo Alto. We have been advocating for a reduction of light pollution in the region, and have engaged with the City of Palo Alto in promoting human and environmental health through reducing, and preventing the proliferation of artificial light at night. Recognizing that the proposed project, a local advanced water purification system, provides important infrastructure, we remain concerned with the lighting plan for the proposed water treatment plant at 2501 Embarcadero in the Baylands area of Palo Alto1.
The State of the World's Migratory Species report, a first-of-its-kind assessment by the Convention on the Conservation of Migratory Species (CMS, an environmental treaty of the United Nations) – paints a stark picture. One in five migratory species listed by the CMS is at risk of extinction and almost half (44%) are decreasing in numbers2. Birds are especially vulnerable since most species migrate at night3.
Lights with lower color temperatures (typically below 3000K) are better for wildlife because they have less impact on the natural behaviors and activities of nocturnal animals4. Nocturnal animals such as birds, bats, and insects rely on natural light cues to navigate and carry out essential functions such as feeding, breeding, and migration. Artificial light sources with higher color temperatures (typically above 3000K) can interfere with these natural cues, disrupting the animals' circadian rhythms and affecting their behavior. For example, high-color-temperature lights can attract insects, which in turn attract birds, bats and other animals that feed on them, leading to changes in insect populations and affecting the ecosystem. Additionally, high-color-temperature lights can cause birds to become disoriented during migration5, leading to collisions with buildings and other structures. Lights with lower color temperatures are less disruptive to wildlife because they produce light that is closer in color to natural moonlight and starlight. This can help minimize the impact of artificial light on nocturnal animals and allow them to carry out their natural behaviors without interference6.
The Staff Report for the ARB meeting of April 4th refers to the DarkSky International "Five Principles for Responsible Outdoor Lighting''7 (PDF p. 31). However, we believe that the Staff Report is inconsistent with Principle Five (Correlated Color Temperature, CCT). The Staff Report provides, “Warm‐colored – Industry standard recommendation is around 5000K to promote safety and alertness.” However, 5000K is not “warm-colored” and contradicts the DarkSky International guidance on that point. Safety considerations are important, but when CCTs values higher than 3000 are used, DarkSky International would recommend additional actions to reduce the impact of this lighting.
The point about higher CCT values for worker alertness (same page) doesn’t take into account the body of scientific research indicating that exposing workers to blue-rich white light at night is associated with health problems8.
In our conversation with experts, it was recommended that Palo Alto use 3000K. Should the City use 4000K white LED lighting, the intensity of the light should be reduced by 50% to achieve the same visual response from observers using the spaces at night. That is because the eye is more sensitive to blue light at lower intensities, so an observer would otherwise perceive scenes to be brighter compared to, e.g., 2700K lighting even if the quantity of light were the same9. Furthermore, higher-CCT lighting yields more ‘discomfort glare’ than lower-CCT lighting10. That can be fatiguing to people exposed to it for long periods of time.
We believe that the City should use a CCT of no more than 3000 Kelvin, and limit the duration and intensity of artificial light at night. Lights should be off when no one is around (a switch, or motion sensors can do this effectively). The intensity of the lighting should be set appropriately (DarkSky Principle #3), taking into account that perception varies according to light color.
Thank you,
Matthew Dodder
Executive Director
Santa Clara Valley Audubon Society
James Eggers
Chapter Director
Sierra Club Loma Prieta Chapter
2 1 in 5 migratory species are at risk of extinction, says a new UN report. World Economic Forum Feb 21, 2024
See also, https://www.cms.int/en/publication/state-worlds-migratory-species-report
3 Burt et. Al. 2022. The effects of light pollution on migratory animal behavior. 2022. Trends in Ecology & Evolution, Special Issue: Animal behaviour in a changing world.
4 Effects of LED Lighting on Terrestrial Wildlife. 2023. State of California Department of Transportation Technical Report. Prepared by Travis Longcore, Ph.D., UCLA.
US Department of Fish and Wildlife. Threats to Birds: Collisions - Nighttime Lighting Protecting our Night Skies for Birds.
5 L.S.A. Huson 2021. Spatiotemporal effects of artificial lighting on migratory birds
6 Effects of LED Lighting on Terrestrial Wildlife and
7 https://darksky.org/resources/guides-and-how-tos/lighting-principles/
8 For example: More exposure to artificial, bright, outdoor night-time light linked to higher stroke risk. 2024 https://www.sciencedaily.com/releases/2024/03/240325172425.htm, American Heart Association. More exposure to artificial, bright, outdoor night-time light is linked to higher stroke risk."
9 Schlesselman B, et al. 2015. Melanopically enhanced metameric white lightings make a simulated sports field appear brighter allowing a trade-off between photopic intensity and melanopic content. In Proceedings of the Illuminating Engineering Society Annual Conference.
10 Huang W, Yang Y, Luo MR. Discomfort glare caused by white LEDs having different spectral power distributions. Lighting Research & Technology. 2018;50(6):921-936. doi:10.1177/1477153517704996; Zhu, X., Det al. (2013). Perception study of discomfort glare from LED road lighting. Light and Engineering, 21(2), 61-68.)