Riverside County, CA Outdoor Lighting: Light Trespass (2026)

Riverside County addresses light trespass - unwanted light spilling onto neighboring property or into the night sky - chiefly through the shielding requirements of Ordinance No. 655 (the Mount Palomar light-pollution ordinance). The ordinance defines two shielding standards designed to keep light from escaping sideways and upward. A "fully shielded" fixture must be constructed so that all light rays it emits are projected below the horizontal plane passing through the lowest point of the fixture (Sec. 4.J). A "partially shielded" fixture must project at least 90% of its light rays below that horizontal plane (Sec. 4.K). Within Zone A (15-mile radius of Palomar Observatory) and Zone B (15-45 miles), many non-low-pressure-sodium fixtures are only permitted if fully shielded, which has the practical effect of reducing glare and spill onto adjacent parcels. The ordinance also imposes curfews: Class I general lighting and Class III decorative lighting must be off between 11:00 p.m. and sunrise (Sec. 8), and advertising searchlights are prohibited in both zones. The ordinance's stated intent is to restrict light fixtures that emit undesirable rays into the night sky; it does not aim to restrict low-pressure sodium security lighting of single-family homes. Outside the Palomar zones, the County does not impose a general numeric light-trespass cap, and neighbor light disputes may instead be addressed under nuisance principles.