When a traditional streetlight’s yellow glow goes out, Pasadena crews increasingly have been replacing them with newer, more efficient technology: LEDs, which illuminate roads with a clearer, whiter light.

This newer technology is in widespread use in cities across the country, including Los Angeles, because they use less energy and last longer. But the American Medical Association warns that there are right and wrong kinds of LEDs — and cities that use the wrong kind can harm residents’ health, including by disrupting sleep.

On the other hand, lighting experts, including leaders of the Illuminating Engineering Society, say the AMA’s position may be overblown, and it’s important not to overlook other safety factors when it comes to lighting cities. Despite that tension, Pasadena is generally using lights that follow the AMA’s recommendations, and Pasadena’s top health official said the city is making responsible lighting decisions.

Currently, there’s not a master plan to replace all of the city’s lights, according to Richard Yee of the Department of Public Works.

“City crews are still maintaining older luminaries and bulbs when they are available, but as supplies and availability are diminishing, they are being replaced with LED alternatives,” Yee wrote in an email. “New LED luminaries are being installed with 3,000 Kelvin or less.”

Lighting science is complicated, but one major factor is a light source’s warmth or coolness, which is measured on the Kelvin scale. The lower on the scale, the warmer the color of the light appears. For example, the amber glow of a candle’s flame is 1,000 to 2,000 Kelvin, while the blue sky is 10,000, according to University College London.

Types of streetlights

There are 17,716 streetlights in the city. One-third of that total are the old-school type: high pressure sodium lamps, which are 2,200 to 3,000 Kelvin, according to a DPW report.

The next most common, just less than one-third of all lights, are 4,000 to 5,000 Kelvin induction lights. Between 2011 and 2015, the city replaced and installed 5,000 of those lights, which have a 20-year life expectancy and save $200,000 in energy costs annually, according to the report.

Mercury vapor and incandescent, with light between 2,700 and 4,000 Kelvin, account for one-quarter of all lights.

Currently, there are just 820 LED lights in the city, ranging from 3,000 to 5,000 Kelvin. That includes 93 installed in 2017 and 89 so far this year, DPW staff said in emails.

But moving forward, the city will install only 3,000 Kelvin or warmer LED lights, according to Yee. The Public Safety Committee studied the issue last year and took input from DPW staff and Dr. Ying Ying Goh, the city’s health officer.

Goh said the city’s lighting plans are responsible, though noted there may be some people whose medical conditions may be affected disproportionately by bluer light.

In 2016, the AMA adopted guidelines that recommended cities limit their use of blue-rich light sources and use fixtures no cooler than 3,000 Kelvin. But resident Donald Berry says technology is constantly being improved, and Pasadena should use LED fixtures that are even warmer. He is circulating an online petition urging the city to do so.

The International Dark Sky Association also recommends cities use 3,000 Kelvin or lower lamps.

“If they’re going to go in that direction, if they’re going to do LEDs, I want them to at least do 2,200 K LEDs,” Berry said. “I think it’s the best for human health and limits the city’s legal exposure.”

Indeed, cities that have installed LED streetlights have been sued. A judge last year ruled against the city of Monterey, finding it needed to conduct a more thorough environmental review before installing LEDs.

In Pasadena, Monterey and cities across the country, advocates have pointed to the AMA’s guidelines as reasons why city officials ought to very carefully consider the types of lights they install.

Lights that emit a large amount of blue — which appears white to the naked eye — can suppress the human body’s production of melatonin at night. That hormone regulates sleep and disruption of it can lead to negative health effects, including obesity, according to the AMA.

But in a position that counters some of the AMA’s arguments, the Illuminating Engineering Society says that more research must be done on the health impacts of lighting before cities make policy decisions.

For now, there’s no citywide plan for converting to LEDs. But public works officials are in early discussions about a possible master plan update that would dictate replacement on a large scale, Yee said.

Los Angeles in 2009 began a five-year, $57 million plan to install LED bulbs in 140,000 streetlights. It was expected to save the city $10 million a year in energy costs.

Other factors go into lighting decisions, including the ability to dim lights and whether the lamp is shielded to reduce scatter in areas other than roads.