Somerville, MA Outdoor Lighting: Light Trespass & Shielding (2026)

Article 10.6, Outdoor Lighting, opens with an Intent and Purpose section that names light trespass by its statutory term: §10.6.2.c states the Ordinance exists 'to minimize adverse impacts of lighting such as light trespass, obtrusive light spillover, and harmful glare,' alongside goals of preserving night-sky visibility and following Illuminating Engineering Society (IES) recommended practices. Section 10.6.3 applies these standards to essentially all outdoor lighting fixtures citywide, exempting only rights-of-way and street lighting, sign lighting, monument lighting, holiday lighting, emergency and law-enforcement lighting, underwater lighting, temporary theatrical or construction lighting, and automatically-timed low-voltage landscape lighting.

The operative anti-trespass control sits in §10.6.4.d, Light Fixtures. In the Neighborhood Residential district, and in the Urban Residential district for every building type except Apartment Buildings, every outdoor luminaire must be 'full cutoff or fully shielded to emit no light above horizontal (ninety degrees (90°) above nadir).' Five narrow exceptions apply: up to two partly shielded or unshielded fixtures at a principal entrance, low-voltage lighting that does not project onto adjacent properties, shielded directional floodlighting aimed so glare is not visible from adjacent properties, open-flame gas lamps, and fixtures on a vacancy sensor that shuts the light off within fifteen minutes of the area being vacated. Every other building type in every other district instead follows a BUG (backlight, uplight, glare) rating system under §10.6.4.d.ii, keyed to Table 10.6.2 and the distance a fixture sits from the property line, and §10.6.4.c separately caps color temperature at 3000 Kelvin or less citywide.