Exterior lighting for buildings, parking lots, city streets and traffic signals can contribute up to 25% of a city's operational carbon footprint. While outdoor lighting and signals are a small percentage of all lighting energy use (public and private) in the city, these uses are important opportunities for city government to address as they work to improve public sector sustainability and night time visual quality in the city. Recent advances in lighting, signal and intersection technologies allow a city to provide better quality and safer lighting for lower costs and energy usage with short capital payback periods (2 to 7 years). Additionally, new smart/internet-of-things (IoT) technology allows added functionality on street lighting. And finally, as city government addresses outdoor lighting, it can then use its understanding of the issues to better work with private owners in the city to improve their lighting.
The 2016 State law MS 16B.328 requires state-funded outdoor lighting fixtures to be energy efficient and dark-sky compliant.
LED street light luminaires are similar in cost to traditional high-pressure sodium luminaires and they last 3-4 times longer, allowing significant cuts in replacement and maintenance costs. They also typically use less than half the energy to put the same light on the roadway, cutting annual electricity savings 30-70%. By installing smart nodes and intelligent sensors the lighting units can provide cities with a digital connection and provide new opportunities to cities to better serve their customers. Such a network can adjust light levels to address crime/emergency responses, provide near-real time data on vehicle, pedestrian, and bicycle traffic, report on weather, air quality, sudden noises, unexpected crowds, include speakers and emergency call-buttons, and relay telemetry from sensors installed in the sewer or water pipes. Poles can also be used to charge EVs, to serve as Wi-Fi hot spots, and can be rented out to mobile or cable service providers.
LED streetlights can be provided in several temperatures allowing for different colors of light. 3000 Kelvin is a warmer color that is closer to that of the old high-pressure sodium. 4000 Kelvin provides a whiter light. While the 4000 Kelvin luminaire has been shown to provide slightly better sight distance, some people prefer the warmer light that the 3000 Kelvin luminaire provides. Recent research shows that there are no differences in impact on human health based on the color temperature of roadway lighting used. Detrimental impacts on wildlife due to lighting vary by species and relative risks are still being researched. Over-lighting can be prevented by doing light level calculations and adding dimming controls to lower light levels during times of day (midnight to 5:00am) when less light is needed. Also, LED technology provides a better ability to direct light so that it is not shining in places it shouldn't be (i.e. people's backyards and into houses).
The U.S. DOE and its national laboratories predict that LED parking lot lights will reduce parking lot energy needs by more than 50% and maintenance costs by more than 80% compared to traditional parking lot lights. For parking lots whose lights are on 24 hours a day, traditional lights must be replaced every two years; depending on the LED luminaire used it may need to be replaced every 6 to 8 years on average. See LED street lighting presentations from the June 2014 League of MN Cities annual conference.
Optimizing signal timing is a low-cost approach to reducing congestion, costing from $2,500 to $4,000per signal, and yielding:
Traffic delay reductions in the average range of 10- 25%.
Fuel consumption reductions in the average range of 5- 10%.
Reduction in harmful emissions (carbon monoxide, nitrogen oxides, volatile organic compounds) up to 22%.