Southborough, MA Outdoor Lighting: Dark Sky Rules (2026)

Section 174-12.1 states its purpose in subsection (A): prevent glare on public roadways, protect the privacy of residents, promote energy-efficient outdoor lighting, minimize light trespass, and curtail light pollution and reduce skyglow. The Planning Board is authorized to promulgate rules and regulations, and it maintains the Rules and Regulations for Outdoor Illumination.

Coverage starts low. Flood or spot luminaries rated at 900 lumens or more, or any other luminaires rated at 1,800 lumens or more, are subject to the section, including on single- and two-family residential lots. Emergency lighting, hazard warning and temporary decorative or holiday lighting are excepted, and a luminaire that lights only a freestanding sign, flag or building wall must be shielded so its direct light is confined to that surface.

Shielding rules sit in several places. Subsection (E)(5) prohibits non-shielded wall-packs, barn lights and floodlights not aimed downward in all zones. Subsection (M) limits parking lot lighting to no light emitted above 90° from the installed vertical axis. Subsection (Q) bars direct light above a horizontal plane through the lowest direct-light-emitting part of a luminaire at the lumen ratings above. Pole-mounted fixtures cannot exceed 20 feet in any zone, and in nonresidential districts a wall-mounted area-lighting fixture cannot be mounted higher than 15 feet above grade and must be shielded to control glare.

Brightness is capped by zone. Lighting zones run from LZ-0 for the Conservation and Research, Scientific and Professional districts to LZ-3 for Business Highway, Industrial and Industrial Park, and Table 1 allows 0.5, 1.25, 2.5 and 5.0 lumens per square foot of hardscape respectively. Proposed LEDs must have a correlated color temperature between 2,200K and 3,000K. Site plan applicants file a lighting plan with BUG rating data, and the Planning Board can waive or modify requirements.