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 MN Dept. of Transportation has lighting performance standards that must be met for State Aid streets. Cities often use these standards for their own streets.
The 2016 State law MS 16B.328 requires state-funded outdoor lighting fixtures to be energy efficient and darky-sky compliant.
LED street lights cost 3-4 times more than traditional high-pressure streetlamps, but last 3-4 times longer, allowing significant cuts in replacement and maintenance costs. They also produce 2-3 times more light per watt, cutting annual electricity savings 30-70%. Because they are electronic components they’re also far more programmable, fitting in with a retrofit program that turns lamp housings into smart grid hubs with microprocessors, cameras, sensors, video display panels, and wireless radios. Such a network can modify light levels to address crime/emergency responses, report on traffic, count pedestrians, 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 Wifi hot spots, and can be rented out to mobile or cable service providers.
LED streetlights that emit warmer colors (3,000 Kelvin or lower) are slightly less energy efficient than more standard 4,000 Kelvin bulbs, are not ‘shockingly bright’ compared to high-pressure sodium lights, and have lower (blue-rich) negative light impacts on human sleep cycles (which, however, are much more impacted by 'screen time') and wildlife, though definitive impacts are still uncertain and relative risks are still being researched. Studies have shown that 4,000K is optimal for road safety and being able to see at night. There are ways however to keep LED streetlights not as bright - doing a solid lumens calculation to avoid over-lighting, and adding dimming controls to bring down brightness during times of day (midnight to 5:00am) when less light is needed. Also, LED technology allows for nice cut-offs so that light is not shining in places it shouldn't be - people's back yards 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; LED lights need be replaced every 10 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 $3,100 per signal, and yielding:
Traffic delay reductions in the range of 14 - 25%.
Fuel consumption reductions in the range of 8 - 10%.
Reduction in harmful emissions (carbon monoxide, nitrogen oxides, volatile organic compounds) up to 22%