Sonoma County, CA Outdoor Lighting: Light Trespass & Shielding (2026)

Sonoma County Code § 26-90-120 sets scenic design standards for homes and related site development in the LG/MTN combining zone, which covers the Taylor, Sonoma, and Mayacamas Mountains. The exterior lighting rules sit in subsection (c)(2)d, under the architectural standards. They apply to single-family dwellings and appurtenant structures, fences included, that are or would be visible from public roads.

The light trespass core is two sentences. Light fixtures cannot sit at the periphery of the property, and they cannot spill over onto adjacent properties or into the night sky. The code then backs that with measurable limits: each luminaire is capped at one thousand (1,000) lumens, and the total illuminance beyond the property line, counting every exterior light operating at once, cannot exceed one (1.0) lux. The 1.0 lux figure is a combined cap, so adding a second compliant fixture does not give a neighbor more light than the limit allows.

The fixture rules are just as specific. Exterior lighting must be downward facing, fully shielded, and mounted at the lowest possible point to the ground to prevent glare and light pollution. Roadway, parking, and driveway lights must be low profile and use full cut-off fixtures. Flood lights are not allowed. Where security lighting is necessary, it must be motion-sensor activated only, so a constantly burning security light is out of compliance.

The standards reach a property through permit review. Under § 26-90-040, each permit that produces exterior modifications or new development in a Local Guidelines combining zone needs Design and Site Plan Review or Administrative Design and Site Plan Review before construction permits issue, and where only a Building, Grading, or Drainage Permit is involved the Director is the review authority. Section 26-90-120(b)(1) requires a recorded deed restriction stating the conditions of that design review approval, so the lighting conditions follow the land to later owners.

Three carve-outs matter. Legal dwellings and structures existing on the effective date are deemed to comply, but expansions must meet the standards. Accessory structures that need no Building Permit, agricultural structures and uses, and farmworker housing are exempt. Structures that are not or would not be visible from public roads at the time of construction are also exempt. A review authority can waive or modify a requirement only if strict compliance would render a legal parcel unbuildable.