Unincorporated San Mateo County regulates outdoor lighting through Zoning Regulations Chapter 22.5 (Dark Sky) and Building Regulations. Exterior lighting must be shielded, downward-directed, and limited to 0.5 foot-candles at residential property lines. Coastal zone and rural areas (La Honda, Pescadero, Skyline) have stricter dark-sky rules.
San Mateo County Zoning Regulations §6405.2 and the countywide Dark Sky provisions require that outdoor lighting be fully shielded and directed downward to prevent light trespass onto adjacent properties and the night sky. Residential fixtures must not exceed 0.5 foot-candles at the property line, and 0.1 fc in coastal and rural zones. All exterior fixtures over 60 watts (or 800 lumens LED equivalent) must be full-cutoff. Floodlights aimed at neighboring homes are prohibited. Security lighting must be motion-activated with a maximum 10-minute timer. Holiday lights are exempt November 15 through January 15. Coastal Development Permits in the Midcoast and Coastside areas (Moss Beach, Montara, El Granada) impose additional restrictions to protect wildlife. Code enforcement handles complaints through the Planning and Building Department.
Notice of violation with 30-day correction period. Continuing violations: administrative fines of $100 first offense, $200 second, $500 third per SMC §1.20.040. Commercial light trespass: up to $1,000. Coastal zone violations may also trigger Coastal Commission enforcement.
San Mateo County, CA
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See how San Mateo County's light trespass rules stack up against other locations.
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