November 7, 2025
Palo Alto City Council
250 Hamilton Ave
Pave ALto, CA 94301
Responses to Comments Received by the City from Stanford
Regarding the Draft Dark Sky Ordinance
Dear Mayor Lauing and Palo Alto City Councilmembers,
In reviewing the letter sent by Stanford University to the City, the Sierra Club Loma Prieta Chapter has some responses that are relevant to consider as Council deliberates on topics raised by this ordinance.
Safety concerns regarding motion sensor outdoor lighting are already addressed by the ordinance
The letter from Stanford states the following.
“Motion-activated lighting does not provide a sense of safety or security, especially in a complex where tenants do not have fixed closing hours. Maintenance, janitorial, and security staff are often on-site after midnight, and researchers and engineers regularly work late as deadlines approach.”
We believe that the concerns raised in this letter would already be addressed by the lighting curfew section of this ordinance, which reads as follows.
“(4) Lighting Control. (A) Lighting Curfew. Unlike other provisions in this section, the Lighting Curfew shall apply to all outdoor luminaires for new and existing buildings and structures, unless otherwise approved. All outdoor lighting shall be fully extinguished or be motion sensor operated by 12:00 a.m., two hours after the close of business, or when people are no longer present in exterior areas, whichever is later.”
The underlined wording of this curfew language is extremely flexible, and allows for consistent lighting in situations where people are still present in exterior areas, even after midnight. In areas in Stanford where people are regularly present after midnight, as claimed in the letter, those areas would be allowed to remain consistently lit, according to the curfew language of the ordinance. The ordinance as-written would not require Stanford to use motion-sensor lighting at times when people are usually or regularly present in certain outdoor areas.
The lighting levels established by the ordinance offer sufficient lighting for public safety, and avoid the hazards of glare caused by overly bright and ‘cool’ lighting.
The letter from Stanford makes the following claim, without citing any scientific studies or specific evidence.
“Requiring changes such as adding motion sensors, shrouds, or altering fixtures and bulbs would lead to poor and unsafe lighting conditions.“
However, DarkSky International’s 2025 State of the Science Report1, which is based on an analysis of more than 500 scientific studies regarding artificial light at night, makes the following conclusions regarding over-lighting and its negative effects on public safety.
“Glare from bright artificial light sources is a particular concern for nighttime safety. It results from intense light rays entering the eye directly from a source. Some of that light scatters inside the observer’s eye, reducing the contrast between foreground and background. This effect makes it difficult to see objects as distinct from what surrounds them. Glare reduces the visibility of objects at night for motorists, pedestrians and bicyclists. Although some older observers report stronger sensations of glare from certain sources, it seems to affect people of all ages2. Some modern lighting sources like LED can make glare worse by emitting considerable light at very shallow downward angles3 and also by using non-uniform light sources with insufficient optical diffusion4. The perception of glare seems to vary with the wavelength of light involved. In general, short-wavelength (‘cool’) light causes stronger glare than long-wavelength (‘warm’) light5.”
The current ordinance, by requiring lights to be fully shielded, prevents the direct light scattering inside the observer's eye that would lead to difficulty seeing objects around them. By avoiding short-wavelength ‘cool’ light, the ordinance avoids the sources of stronger glare that would also reduce nighttime visibility. By ensuring that lighting is not unnecessarily bright at night, the ordinance allows for pedestrians to clearly view lit areas while maintaining situational awareness of their nighttime surroundings. Regarding motion-sensors, we have already established previously in this letter that the existing curfew language is flexible to allow for consistent lighting in outdoor areas where people regularly present after midnight.
The ordinance, as written, adheres to the science regarding light pollution and public safety. We are concerned that if the ordinance is modified to allow for un-shielded, brighter, and ‘cooler’, lighting, that those modifications would actually have a negative effect on public safety, according to the scientific literature on this subject.
Furthermore, Palo Alto’s Police Department was consulted by the City regarding the standard of 2700 Kelvin for lighting fixtures, and found that threshold acceptable for public safety.
The ordinance as written establishes clear precedence for state and federal laws.
The letter from Stanford makes the following claim.
“We are also concerned about potential conflicts with California Title 24 and Cal/OSHA lighting\ requirements. These state and federal standards may supersede local regulations, rendering parts of the proposed ordinance unenforceable. We urge the City to carefully evaluate these overlaps to avoid legal and practical inconsistencies.”
The letter does not identify any specific conflicts with state or federal law in the ordinance as written. Furthermore, the ordinance contains language that already addresses these concerns in the following section.
“(i) Additional Provisions and Conflict Precedence. Lighting required by the Building Code, Fire Code, or state or federal law shall additionally comply with the requirements of this section, unless these requirements necessarily conflict with the aforementioned Codes and laws. In the event of a conflict, the standards in the applicable Codes and laws shall prevail.”
Since no specific conflicts with state or federal laws have been identified, and the ordinance clearly establishes the precedence of state and federal laws, we believe no modifications to the draft are necessary at this time to address this topic. Should unforeseen conflicts arise after adoption, the ordinance is already equipped to address them.
In Conclusion
We hope that our explanations provide sufficient justification that the draft ordinance is already equipped to resolve the concerns from Stanford noted above.
Sincerely,
Dashiell Leeds
Conservation Coordinator
Sierra Club Loma Prieta Chapter
1 https://darksky.org/app/uploads/2025/06/ALAN-State-of-the-Science-2025-EN-2.pdf
2 Davoudian, N., Raynham, P. and Barrett, E. Disability glare: A study in simulated road lighting conditions. Lighting Research & Technology, 46(6):695–705, nov 2013. doi: 10. 1177/1477153513510168.
3 Kyba, C.C.M., Hänel, A. and Hölker, F. Redefining efficiency for outdoor lighting. Energy Environ. Sci., 7(6):1806–1809, 2014. doi: 10.1039/c4ee00566j.
4 Yang, Y., Luo, M.R. and Ma, S. Assessing glare. part 2: Modifying unified glare rating for uniform and non-uniform LED luminaires. Lighting Research & Technology, 49(6):727– 742, apr 2016. doi: 10.1177/1477153516642622
5 Bullough, J. Spectral sensitivity for extrafoveal discomfort glare. Journal of Modern Optics, 56(13):1518–1522, jul 2009. doi: 10.1080/09500340903045710