Light Pollution and Palomar Observatory

Artificial light in the Palomar sky looking SW toward Escondido. (Palomar/Caltech)

This partial panorama looks southwest (left), through north (center, towards the Hale Telescope dome), to northeast (right). It reveals the sky glow caused by lights in San Diego County (left), Riverside County (center), and Palm Springs (right). Photographed February 4, 2005. (Palomar/Caltech)

Light pollution is a term we use to describe the adverse effects of artificial light. Some adverse effects can be biological: excessive ambient nightime light can be disruptive to some plants and animals (so-called ecological light pollution). For professional and amateur observers alike light pollution degrades our ability to observe and enjoy the natural night sky.

Light pollution is an increasing problem for observatories everywhere, and for Palomar Observatory in particular. Back in the 1930s one of the main reasons Palomar Mountain was selected as the site for the 200-inch telescope was its dark skies that would allow observation of the faintest galaxies without the interference of city lights. Since the 30s, rapid urbanization of Southern California has resulted in a significant increase in the amount of sky glow—and directly impacting the effectiveness of the Palomar Observatory for many types of astronomical research.

Since the 1980s Caltech and Palomar Observatory have worked extensively with the surrounding communities to minimize the impacts of light pollution on the observatory's research mission. We are grateful for this ongoing partnership with neighboring communities in Southern California, and will continue to work with City, County, and Tribal governments to mitigate the effects of local light pollution. With continued community support Palomar's research mission can continue, and we all can enjoy the natural beauty of the night sky.

Local Light Pollution Ordinances


California Title-24 Energy Requirements and Standards for Outdoor Lighting and Signs.


Riverside County's Light Pollution Ordinance (No. 655)

San Diego County's Light Pollution Ordinance - Choose "Frames" or "No Frames" and then put "light pollution" into the search window

San Diego County's Dark Skies and Glare Guidelines for Determining Significance (Draft Version)

San Diego county light zone map

City Ordinances Within San Diego County

City of Chula Vista

City of Escondido - Article 35 Outdoor Lighting Ordinance

Reducing Outdoor Retail Lighting - a brochure from the Escondido Police Department

City of Encinitas Section H and I

City of Imperial Beach Lighting Regulations

City of Oceanside Light Pollution Regulations - Chapter 39

City of Poway 17.08.220 Section L

City of San Diego Lighting Code

City of San Marcos (search for lighting in the document)

City of Vista (pages 10 - 13)

City Ordinances within Riverside County

City of Murrieta's Mount Palomar Lighting Standards (16.18.110) or visit, choose frames or no frames and enter 'Palomar' in the search window.

The City of Temecula adheres to Riverside County's Light Pollution Ordinance (No. 655)

Additional Light Pollution Resources

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Light Pollution / v 1.0
Last updated: 28 May 2015 ACM/AFB