Milligan Parking Lot Impacts of Lighting on Riparian and Aquatic Ecosystems Along the Guadalupe River

Joint letter logos

June 9, 2024

To Mayor Matt Mahan and Members of the City Council

Subject: Item 5.1 on the 6/11 Agenda Actions Related to the 8820 - Milligan Parking Lot Project

Dear Mayor Mahan and Councilmembers,

The Santa Clara Valley Audubon Society (SCVAS) and the Sierra Club Loma Prieta Chapter have reviewed the Environmental Impact report (EIR) for the Milligan Parking lot, with special attention to the potential impacts of lighting on riparian and aquatic ecosystems along the Guadalupe River. The Project seeks to build a surface parking lot adjacent to the Guadalupe river, and to exempt this parking lot from the 100-ft setback requirements of the City’s General Plan and the Valley Habitat Plan.

We do not understand the logic driving the need for an exemption that would prioritize parking over the Guadalupe River. Parking should be an order of magnitude lower on San Jose’s priority scale compared to the health of the environment.

The most recent “Artificial Light at Night: State of the Science 2024”1, published by DarkSky international in June 2024, highlights the immense and pervasive harm that artificial light at night inflicts on ecosystems and species.

The EIR acknowledges,

“The project’s parking lot lighting could result in a significant impact to sensitive habitat and species along the Guadalupe River due to spillover illumination affecting foraging activity, increasing predation risk on fish and changing the composition of fish communities that occur across a day-night period.“


and proposed mitigation measures (MM Bio-2-1,Bio-2-2, Bio-2-3)

  1. The most adequate mitigation would be to adhere to the 100-ft setback requirements, and to plant a vegetated buffer that can help shield the river from the impacts of the parking lot. This would protect the river at the cost of just a few parking stalls.
  2. Overall, the proposed Mitigation Measures align with DarkSky International’s Five Principles for Responsible Outdoor Lighting2, uses the BUG system3 as indicated by the California Building Code Title 24, and seeks to reduce the intensity of lighting after 10PM. This is a commendable approach, but the location of the project a stone-throw from the riparian corridor of the Guadalupe River merits additional caution. To further reduce the impact of lighting we suggest:
    • Avoid all lighting of the Guadalupe River. The proposed BUG rating of B0 still allows some light to spill into the creek (as noted in the EIR). If avoidance is not feasible consider using an appropriate, wider setback.
    • Lighting poles locations must be positioned to ensure that there is no direct illumination of the river. This may be difficult in this location and at the narrowed setback from the river. Consider implementing 100-ft setback, or use fixtures from manufacturers that offer additional shielding that makes the cutoff angle in the backward direction steeper than it would be otherwise with the default design. These are sometimes described as “house-side shields” intended to prevent backlight from street lights falling on buildings set back from the street some ways.
    • For the lighting nearest the river, use phosphor-converted amber (“PC amber”) LED lighting as an alternative in order to reduce the blue light emissions further. The International Dark Sky Association has a list of PC Amber lighting products, including many street/area lighting options4.

While the proposed mitigation measures for Milligan parking lot lighting are largely in line with responsible outdoor lighting practices, additional steps could be taken to avoid or further reduce environmental impact. Adopting appropriate setbacks and ensuring minimal light pollution, particularly towards the river, and low blue light options will contribute to a more sustainable and environmentally friendly lighting solution.


Thank you for considering our comments.

James Eggers
Chapter Director
Sierra Club Loma Prieta Chapter

Shani Kleinhaus, Ph.D.
Environmental Advocate
Santa Clara Valley Audubon Society

1 https://darksky.org/app/uploads/2024/06/ALAN-State-of-the-Science-2024-EN.pdf, see also https://www.zotero.org/groups/2913367/alan_db/

2 https://darksky.org/resources/guides-and-how-tos/lighting-principles/

3 The Backlight, Uplight, and Glare (BUG) rating system is a Title 24 Building Code requirement for outdoor lighting in California that indicates how well lighting reduces Backlight, Uplight and Glare.

4 https://darksky.org/what-we-do/darksky-approved/products-companies/#!/PC-Amber/c/30926016