This post has been updated to include information about San Francisco's choice of yellow-rich LEDs.
Streetlights don’t make a lot of headlines. They are a constant in our cityscapes, rarely drawing the attention of passing pedestrians and motorists.
Photo by flickr user meltedplastic
That is, until recently. During the past few years, cities from Baltimore, to San Antonio, to Los Angeles have begun replacing traditional streetlights (typically high pressure sodium bulbs) with newer light-emitting diode bulbs (LEDs). Last year, Oakland, CA joined the ranks of the LED converts with its Streetlight Conversion Project, switching out 30,000 of the city’s 38,000 regular bulbs for LED substitutes. Later this year two other California Bay Area cities, Berkeley and San Francisco, will follow in Oakland’s footsteps with LED conversion projects of their own, converting 8,000 and 18,500 streetlights respectively.
The hype around LEDs stems from two primary benefits. First, LEDs are brighter than traditional lights, and many cities feel that the increased brightness improves public safety. Second, LEDs are more energy efficient than earlier generation bulbs, bringing both financial and environmental benefits to converting cities.
Public safety was a big motivator behind the Oakland conversion project, and it may seem intuitive that brighter lights improve safety. However, some studies suggest that though brighter streets make people feel safer, they have no impact on actual crime levels.
In terms of the environment, LEDs definitely bring some benefits, the biggest of which is energy savings. The Oakland Streetlight Conversion Project will save the city nearly $20,000 per year in energy costs, and will reduce city greenhouse gas emissions by approximately 40 percent (or 80,000 pounds) per year. “The overall goal of this whole project was to have better light in our city streets,” says Kristine Shaff, a public information officer with the City of Oakland. “And the energy savings are tremendous.”
Similarly, Berkeley and San Francisco estimate that new LED streetlights will consume 50 percent less energy than existing streetlights.
LEDs are available in a variety of color temperatures, typically ranging from “warm” yellow-rich lights, to “cooler” blue-white lights. LEDs in the blue-white range are generally 10 to 15 percent more energy efficient than warmer LEDS, leading many cities to opt for the blue-rich bulbs. (The yellow-rich LEDs still provide significant energy savings compared to other common streetlight bulbs).
Unfortunately, exposure to blue-rich light at night can lead to decreased melatonin secretion in humans. Melatonin is a hormone secreted at night by the pineal gland that helps balance the reproductive, thyroid, and adrenal hormones and regulates the body’s circadian rhythm of sleeping and waking. Lower Melatonin levels have been tenuously linked to increased risk of cancer.
Exposure to blue-rich light also disrupts natural sleeping and eating patterns in wildlife. “In an area that has a lot of blue-rich white light, you would stay alert, you would stay as if it was day,” says Bob Parks, executive director of the International Dark-Sky Association, a nonprofit that works to raise awareness about the hazards of light pollution. “Now, people can certainly close their blinds and block-out that rich blue-white light. The problem is that every other species on the planet can’t do that, so you have an impact on everything else. And not just animals — we are talking plants, trees, right down to one-cell organisms. Every living creature has this circadian disruption issue.”
Luckily for Bay Area residents, Oakland, Berkeley, and San Francisco have all chosen to install LEDs on the yellow side of the spectrum. The yellow-rich LEDs are still brighter than the streetlights they are replacing, but are less likely to disrupt either people or wildlife than blue-rich LEDs. “Most of the cities that have been doing a really good job [using yellow-rich LEDs] are in California,” says Parks.
In addition to energy savings, LED streetlights also help reduce waste. LEDs have a significantly longer lifespan than traditional sodium and fluorescent bulbs, lasting for 50,000 to 100,000 hours, or two to five times longer than traditional streetlights. This longer life span means fewer bulbs in landfills. Because LEDs contain no toxic materials, they are also recyclable. Additionally, LEDs are compatible with adaptive controls, which, when installed in streetlights, allow cities to dim and even switch-off streetlights when there is little pedestrian or vehicle traffic.
If we can overlook their bright, sometimes glaring appearance, and encourage cities to use yellow-rich LEDs rather than their blue-rich cousins, it seems that LED streetlights are a good thing. And because LED technology is progressing rapidly, LEDs of the future are likely to help cities save even more in energy costs and greenhouse gas emissions.