Streetlights: How to save your city millions of dollars by changing light bulbs
And the reason why some streetlights are different colors
Ever wonder why some streetlights are different colors? For many years the gold standard of streetlight was a type of light bulb called “high pressure sodium” (HPS). These bulbs were designed with a goal of efficiently providing a lot of light from a large bulb across a large footprint without getting too hot. The light emitted by HPS bulbs is yellow or orange because electricity running through the bulbs vaporizes sodium inside the bulb (sometimes why these are referred to as sodium vapor bulbs) which then produces light on the yellow/orange spectrum. This is a good thing: orange light is less disruptive to vision at night when switching from light to dark, hence why this color is used to illuminate many things from fighter jets to 80’s luxury cars (now you know why the gauges in those older BMWs were orange!).
The newest lightbulb technology today is called LED or “light emitting diode” bulbs. LEDs can emit the same amount of light at a fraction of the energy while lasting longer and while producing less heat. The obvious theory for saving money by converting to LED streetlights is the same as saving money from changing the light bulbs in your house to LEDs. But imagine the scale of that impact in changing streetlight bulbs: a city may have tens of thousands of streetlights, all of which are much larger than a bulb in your house and that have to be turned on every minute of every night.
Read below to learn more about how you can save millions of dollars from this simple streetlight upgrade.
The basics: how streetlights work
Streetlights are installed with the intention of improving visibility and safety on streets and sidewalks. Most streetlights are placed on very tall poles to avoid getting hit by passing tall vehicles or trucks and also to be able to shine across a wider footprint. Streetlight poles also usually have a breakaway feature if they do get hit to minimize damage to vehicles. The lights are spaced apart to try to cover the most amount of area with the least amount of of hardware. For that reason, streetlights are bright and shine over a wide area.
Some streetlights are lower to the ground to better illuminate areas with more pedestrian traffic. These streetlights are typically found in dense urban areas and have poles are much more decorative compared to the long, tall, skinny poles designed for roads and highways.
Streetlights do not usually have a switch to turn them on; instead, light sensors either on the top of streetlights or somewhere nearby can trigger them to turn on at dusk and off in the morning. These sensors usually are not on every single streetlight to save costs.
The color or “color temperature” of streetlights (and all lights actually) varies and is measured in “Kelvin” (e.g. 5000K) and the higher the Kelvin number the whiter the light. HPS lights have a color temperature of around 1900K or 2000K (more yellow/orange). Most LED streetlights installed now are around 2700K and the light looks and feels more natural. Early versions of LED streetlights had a much higher color temperature of 4000K or more, which for many people is reminiscent of a hospital operating room and often visually discomforting particularly at night.
The biggest benefit of LEDs is their energy efficiency and useful life: an LED bulb not only uses 40-50% less energy, it can last 10-20 years or more compared to 5-10 years for a standard streetlight.
Do streetlights do anything else?
Streetlight poles can be a convenient plug in ready power source and mounting location for a variety of other types of technology, including:
motion sensors that can dim lights when no activity is detected
cell phone service towers (4G and 5G in particular)
parking space sensors to track vacant street parking spaces
vehicle and pedestrian counters
weather sensors (temperature, wind, rain, pressure, etc.)
shot spotter (sound analysis software that can triangulate the location of gunfire)
Electric car charging stations
Anything that needs electricity can be connected to a streetlight pole at a fraction of the cost of constructing a new power supply and building a new pole.
Who owns streetlights and how do you pay the electric bill for them?
Streetlights are usually owned by either a government agency (city, county, state, or whoever owns the roads along which they are installed) or by a local utility company (the electric service provider in the area). Sometimes streetlights are owned by an HOA or neighborhood or business district but usually only if those streets are privately maintained.
Paying the electric bill for streetlights is different than with your home: instead of tracking usage at individual meters for each streetlight, utility companies charge what is known as a “tariff”. The tariff is calculated by estimating the energy usage over the course of a year either from measured energy use of a sample streetlight and/or from manufacturer calculations, with the assumptions that all streetlights use the same amount of energy and they will all be on from sunset to sunrise every single day. Sometimes utility companies (or cities) will check these estimates with sample meters on a few streetlights just to make sure.
The key here is that tariffs are often negotiated. In exchange for not requiring meters (or service workers to check the meters), and also considering how much energy a city will be using (usually in the millions of dollars a year for a midsize city or larger), the local utility company hopefully will be a good partner with the city and not make you pay full price.
When upgrading bulbs from HPS to LED, the tariff has to be renegotiated given the far lower energy use.
How replacing your streetlights can save your city millions of dollars
Thinking back to the above points about how LED bulbs use 50% less energy and can last 2-3 times longer: simply replacing your old HPS streetlights with LED bulbs can save you 50% of the cost of energy and more than 50% of the cost of replacement over time. A case study in Kansas City: in 2021 we began the process to replace nearly all of the old HPS streetlights (more than 90,000 at the time) with LED streetlights and saved $5 million a year because of the reduced energy cost and longer useful life. At the time, the annual streetlight energy and maintenance budget was $13 million. That is a huge number just from changing some light bulbs!
However, also keep in mind that the cost to replace the “luminaire” (the industry term for the streetlight bulbs) can be $200 or more, meaning it could cost millions up front to replace all of your streetlights. Knowing that your city will be saving millions of dollars in the future from reduced energy usage and maintenance costs of LEDs, think about how you might be able to balance that savings and spreading out the large up front cost. Using the example above from Kansas City, if you will be able to budget $5 million less per year for streetlights (once all the bulbs are replaced), and it costs $18-20 million to replace all 90,000 of the bulbs, you might be able to pay for the new bulbs in installments of $3-4 million a year for the next 5-7 or so years so that you still have up front savings and don’t have to find new cash to pay for these separately. Some cities will restrict the new luminaires for all future replacements only when bulbs burn out or break. But only do this if you (and your residents) will be comfortable with multi colored streetlights for a few years.
Dark Sky certification: the environmental gold standard
One interesting complaint you will hear about streetlights is that they can disrupt the biological clock of wildlife (birds that live in trees right under streetlights, sea turtles looking for cover of darkness to lay eggs, and any other nocturnal animals). Efforts to mitigate these issues are led by a group called Dark Sky International, which certifies individual products that properly mitigate light pollution and also places that fully commit to minimizing the impacts of light pollution. These steps include:
shielding and filters around bulbs to direct light down and limit glare
a maximum light color temperature of 2700K
avoiding over lighting (too many fixtures in a given area)
use of dimmers where possible
Why are some streetlights purple or blue?
This was not on purpose. Due to a defect with the LED bulbs themselves, the chemical coatings and filters inside the bulb degraded, causing the bulbs to emit more of a blue or purple color. Hopefully most of these defective lights have been replaced by now, but if you see one, please report it to your local government officials to be replaced!
