Accommodating a request by the City of Edmonds, the Snohomish County Public Utilities District (PUD) has delayed until 2017 a planned upgrade of approximately 2,600 Edmonds streetlights to modern LED technology.
Neil Neroutsos, PUD spokesperson, said the upgrade is part of a multi-year project that began in 2013, to convert streetlights throughout the PUD service area to LED lighting. “The technology has greatly improved over time,” Neroutsos said, “offering up to 70-percent energy savings, improved reliability and better color lighting for driver and pedestrian safety.”
But concerns have been raised. Earlier this year the American Medical Association issued a statement about possible negative effects of the light spectrum emitted by “poorly designed” high-intensity LED streetlights. According to the AMA report, these fixtures can emit high levels of blue light that can both contribute to nighttime glare and potentially disrupt circadian rhythms in humans and animals.
The AMA statement concludes that communities should be careful “to minimize and control blue-rich environmental lighting by using the lowest emission of blue light possible.” Read the AMA statement here.
Other reports published by the U.S. Department of Energy, academic and industry groups acknowledge the AMA concerns, but question its conclusions and stress the numerous advantages of LED street lighting, including energy efficiency, better illumination and safety.
Neroutsos said the Edmonds changeout was originally scheduled to begin on Oct. 10, but has been delayed to give City of Edmonds and PUD officials time to discuss the issue. “As a result, the PUD is working with the City of Edmonds to accommodate its request to convert its street lighting to a 3000 Kelvin color temperature as part of the city’s LED lighting installation,” he said.
So what is Kelvin color temperature and what does it mean in terms of streetlights?
Degrees Kelvin is a way of expressing the relative color of a light source, where higher numbers indicate a “colder” (i.e. more blue-rich) light, and lower numbers a “warmer” (i.e. more reddish) source. The Kelvin temperature scale is an adaptation of standard Celsius scale, but where zero Celsius is the freezing point of water, zero Kelvin indicates “absolute zero,” the theoretical point at which all molecular motion ceases, equivalent to –273.15°C or –459.67°F.
When applied to light color, the Kelvin scale indicates the color spectrum emitted by a theoretical black body when heated to a given temperature, and is a quantitative way of expressing common concepts such as “red hot” and “white hot.”
LED streetlights are available in a range of color spectra varying from blue-rich (4000K) to a warmer (3000K) color, all of which more closely mimic natural daylight (5000 to 6500K depending on the time of day and atmospheric conditions) and render colors more truly than the traditional yellowish high-pressure sodium streetlights (2000-2500K). For comparison, standard incandescent lamps are 2500K, moonlight is 4100K, standard fluorescent tubes are 5000K, and computer LCD or CRT screens vary from 6500-9500K. (More information on the Kelvin scale as a measure of light color is available here.)
According to City of Edmonds Public Works Director Phil Williams, in designing the street light conversion, the PUD and the City of Edmonds looked at several lighting industry studies, in addition to recent recommendations from the American Medical Association. After reviewing the options, the city opted for LED lights with a maximum Color Corrected Temperature (CCT) of 3,000 degrees Kelvin, “to create a good balance between whiter appearing LED light and warmer-colored LED light sources,” Williams said.
The City of Edmonds asked the PUD to incorporate this preference into their conversion project and the agency agreed to do so, he added.
“Incorporating the city’s request will delay the start of SnoPUD’s street light conversion project by approximately 90-180 days, which means the conversion is expected to begin sometime after January 2017,” Williams said. “We want to thank SnoPUD for pursuing this conversion project and for accommodating the City’s preferences.”
The PUD Board of Commissioners is scheduled to hear a staff report on LED street lighting at its upcoming meeting on Oct. 18. Agendas and materials will be posted on the PUD Commission website prior to the meeting.
— Story and photo by Larry Vogel