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

Longmont's outdoor-lighting section names light trespass specifically among its purposes: the standards exist in part to 'minimize adverse off-site impacts of lighting such as light trespass and obtrusive light' (§ 15.05.140.A.4). The numeric backbone is § 15.05.140.G.7: 'the amount of nuisance glare (light trespass) projected onto a residential use, greenway or natural area from another property shall not exceed 0.1 footcandles at the property line.' Getting there is a design obligation, not just an outcome to hit after the fact. Section G.3 requires that 'light sources shall be concealed or shielded to minimize the potential for glare and light pollution,' G.4 requires the luminaire angle be mounted at zero degrees, vertical to the ground, and G.5 bars aiming any light source toward a property boundary or adjacent right-of-way.

Operating hours matter too: G.9 requires that 'light fixtures not necessary for security purposes shall be reduced, activated by motion sensor devices, or turned off during hours when the business or use is not open,' so a floodlight left burning all night for no operational reason is itself noncompliant even if it tests under 0.1 footcandles. New development and redevelopment must prove compliance up front with a photometric site plan stamped by a licensed engineer or architect (§ 15.05.140.C), and the director can order changes to lighting after installation if it turns out not to meet the standard (§ 15.05.140.F.4).

Single-family homes are exempt from the plan requirement but any lighting they add is still bound by G.3, G.7 and G.9, and city-owned outdoor recreational fields have their own, more permissive cap of 2.0 footcandles at the property line under § 15.05.140.D.5.b.