U.S. cities are overhauling old lighting systems with energy efficient LED streetlights, as the energy efficient lights are much brighter than conventional lights, and provide higher cost-saving capacity. However, blue-rich LED lights can disrupt the circardian rhythm of humans, animals, and even plants according to an article by Earth Island Journal.

More cities in the U.S. from the East Coast Baltimore to the West Coast Los Angeles are replacing traditional high pressure sodium bulbs with LEDs. In the state California, cities such as Oakland have joined the Streetlight Conversion Project, and will be retrofitting 30,000 out of 38,000 city streetlight bulbs with LEDs. The project is expected to save the city US$ 20,000 per year. Berkley and San Francisco are also following up with the replacement of 8,000 and 18,500 streetlights respectively. 

Despite of LED streetlight’s many benefits, blue LED streetlights which are favored by some cities because of its higher energy efficiency than warm color LEDs can lead to circadian disruption in organisms. Exposure to blue light at night can lead to decreased melatonin secretion in humans, a key hormone that regulates the body’s circadian rhythm. Lower melatonin levels have been linked to increased risk of cancer.

Furthermore, while humans can block out the blue lights with shades and blinds, other living organisms do not have this option. ““In an area that has a lot of blue-rich white light, you would stay alert, you would stay as if it was day,” said 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.”

Luckily for Californians, most cities in California have chosen to use warm colored LEDs that are less likely to trigger circadian rhythm disruptions, according to Park. City authorities might need to evaluate the potential environmental effect from cooler colored LEDs upon local wildlife before installations.