Light pollution is artificial light that goes where it is not needed or wanted. In parking, the main sources are surface lots and the top levels of parking structures, whose lighting can brighten the night sky, spill onto neighboring property and create glare.
Light pollution has three common forms. Skyglow is the brightening of the night sky from light emitted or reflected upward. Light trespass is light spilling past the property line, onto homes or streets. Glare is excessive brightness in the field of view that reduces visibility or causes discomfort.
How parking lighting causes it
- Fixtures that emit light above the horizontal, such as older non-cutoff luminaires.
- Tall poles near property lines and poles on garage roofs visible from a distance.
- Over-lighting beyond recommended levels, and lights left at full output all night.
- Bright, high-reflectance surfaces under strong light.
How to limit it
- Use full-cutoff or fully shielded fixtures with low uplight ratings. See cutoff luminaires.
- Design to recommended illuminance, not beyond, following Illuminating Engineering Society guidance. See IES.
- Use controls that dim when areas are unoccupied. See adaptive lighting.
- Set back and shield roof-level poles, or use lower fixtures on parapets where code and security allow.
- Choose warmer color temperatures where local dark-sky rules call for them. See DarkSky International.
The Parkonomics view
The roof of a parking garage is often the brightest thing in a neighborhood at night, and it rarely needs to be. Good lighting design puts light on the parking surface, at the levels people need, for the hours they are there. Everything else is cost, energy and a neighbor’s complaint.
Related terms: Light Trespass, Glare, Cutoff Luminaires, Non-Cutoff Luminaire, Adaptive Lighting, DarkSky International