Thornton, CO Outdoor Lighting: Light Trespass & Shielding (2026)

Section 38-442(a) sets a single, citywide performance standard rather than a numeric footcandle table: all exterior and interior lighting must be designed and installed so that direct rays are confined to the site on which the lighting is located, specifically to protect adjacent residential properties from glare. The code declares glare that escapes onto neighboring residential land "a public nuisance," tying it into the broader enforcement mechanism in § 38-452(b), which lets the city pursue abatement of any environmental nuisance condition through a restraining order or injunction from a court of competent jurisdiction.

Subsection (b) adds a second, unrelated prohibition in the same section: no one may install or erect lighting that simulates, imitates, or conflicts with warning signals, emergency signals, or traffic signals, a public-safety measure distinct from the residential light-trespass rule in subsection (a). Because § 38-442 falls under Article X, Division 3's environmental regulations, it is exempt for any city project the city manager determines necessary to maintain or protect public amenities, facilities, or infrastructure, per the purpose section at § 38-440(b).