Dark Sky Regulations

shielded-vs-unshielded-bad-better-best-2023 IDA


Key Code Changes to §22.02.001  Definitions


Rather than requiring complex field measurements of light, the approach the city has taken is to treat light pollution as a nuisance.  This approach requires much less from the city and provides the flexibility to address complex lighting issues.  

With the update, the definition of a nuisance is: 

"Any offensive or unpleasant condition which substantially interferes with the use an enjoyment of one's property or which endangers one's health or life or property by causing unreasonable discomfort or annoyance to persons of ordinary sensibilities attempting to use and enjoy their property. A light nuisance is further defined for backlight, upplight, glare, light trespass, and light pollution."


Key Code Changes to §25.01 Principles & Application


The Dark Sky principles were implemented into the city code:

  • All outdoor lighting shall have a clear purpose.
  • Light shall be directed only where it is needed to eliminate light trespass and minimize light pollution.  Full shielding is required.  
  • Light shall be no brighter than necessary to meet its purpose.  
  • Lights shall be used only when needed; a lighting curfew is defined.  
  • Lighting shall have a color temperature of less than 3,000 degrees Kelvin. 
  • Lighting shall be installed to promote the even distribution of light while minimizing sharp contrasts between lit areas and the darker surroundings.  

Key Code Changes to §25.01 Lighting Curfew


A strict light curfew was not felt to be necessary, but some requirements were implemented to reduce lighting when it is not needed.  

With the update, the requirements for the lighting curfew are: 

  • Lighting shall be used only when needed.  Lighting shall be dimmed by at least 30% or extinguished during the curfew hours.
  • For residential properties, the curfew is midnight to one hour before daylight.
  • For all other properties, the curfew is one hour after closing to one hour before opening. 

Key Code Changes to §25.01 Grandfathering


When a law or code is changed, it generally does not apply retroactively - existing properties do not have to comply unless they make changes above a certain threshold.  This exemption from the new code is called "grandfathering".     

The thresholds for losing grandfathering for the updated lighting code are: 

  •       The property owner repairs or replaces more than 50% of their lighting. 
  •       The property owner increases the building or parking area by more than 50% . 

Low-intensity light strings, ornamental lighting, and lighting for entrances and walkways are automatically exempt. Uplighting for certain uses such as flag poles, church steeples, and public art may be granted exemptions.    


Key Code Changes to §25.02  Total Site Lighting


Guidance for the total amount of light installed for new sites is specified without calling for field measurements of light - using the IDSA procedure called the "prescriptive method", the manufacturer's ratings for lights and the site area are set by a simple formula.  

The updated code defines a base amount of lighting as 2.50 lumens per square foot of hardscape.  Additional lighting is allowable in certain situations such as specified residential, commercial, and special zoning districts, drive-up windows, and gas stations.