Boulder, CO Outdoor Lighting: Dark Sky Rules (2026)

The city council adopted Boulder's outdoor lighting standards in 2003 specifically to conserve energy, cut light pollution and glare, and preserve what Section 9-9-16(a) calls 'an environmentally sensitive nighttime environment that includes the ability to view the stars against a dark sky so that people can see the Milky Way Galaxy from residential and other appropriate viewing areas.' Every property in the city had to come into full compliance by November 16, 2018, and any fixture installed after that date must carry a correlated color temperature below 3,001 Kelvin.

The shielding rules in subsection (d) do the real work. Any lamp or bulb under nine hundred lumens in a residential zone must be in a fully shielded fixture, or otherwise obscured by frosted or milk-colored diffusing material. Unshielded fixtures between nine hundred and twelve hundred lumens are allowed only on a motion sensor that shuts the light off within five minutes and cannot be triggered by activity off the property. Upward-aimed architectural facade lighting is capped at nine hundred lumens and must be fully shielded and confined by eaves or overhangs; anything brighter must be aimed downward and mounted flush to the wall. Full cutoff fixtures must be installed level, in a horizontal position as designed, and strings of lights on nonresidential property are barred except under an approved outdoor lighting or landscape plan using bulbs of fifty lumens or less. A flagpole spotlight is capped at thirty-five hundred lumens and must sit as close to the base of the pole as reasonably possible.

Chapter 9-16-1 supplies the definitions the section relies on, including 'full cut-off light fixture,' 'fully shielded light fixture' and 'light pollution.'