By PETER SUR
Tribune-Herald staff writer
The hundreds of new lime green LED streetlights in Waimea and Hilo are the vanguard of an islandwide conversion from the low-pressure sodium lights that have been an island staple for decades.
The county Traffic Division of the Department of Public Works is drafting an amendment to the lighting code that would allow the conversion of streetlights to continue on all county roads, with energy savings of around 60 percent compared to low-pressure sodium lights.
From the mid-1980s until early 2011, most outdoor streetlights were required by law to be of the low-pressure sodium variety. Then last year, the Hawaii County Council approved a bill that allowed the conversion of some low-pressure sodium streetlights into brighter, more efficient light-emitting diode streetlights.
That bill stated that the streetlights could be converted only if they were within a quarter-mile of an intersection or within 100 feet of marked crosswalks. The lights were also required to have less than 2 percent blue light emissions, because of concerns by astronomers.
Low-pressure sodium lamps are favored by the astronomy community because their light emissions fall within a very narrow region of the amber-orange visible spectrum, leaving most of the other visible light frequencies untouched. Other light sources, including incandescents and white LEDs, spread out their emissions over a much broader portion of the visible spectrum, causing interference for astronomers and forcing them to increase the amount of time for observations.
But while monochromatic low-pressure sodium lights are ideal for observing the heavens, they aren’t as safe for drivers who rely on them to navigate Big Island roadways. Common complaints include the similarity of the streetlights to yellow traffic lights, visibility problems during the frequent rain showers, and the poor color rendition that makes it difficult, for example, for people to find their cars.
The initial lights were installed around the Manono Street-Kamehameha Avenue intersection in Hilo, near the Wailoa Bridge. Although power use fell by 72 percent, the test streetlights weren’t bright enough and still emitted too much blue light. The county Traffic Division of the Department of Public Works switched to a newer design that used a filter to reduce blue-light emissions to about 1 percent.
Unshielded blue light emissions are considered harmful for astronomical observations because of the way it scatters in the atmosphere, reducing visibility.
The new lights are expected to last at least four times longer than the low-pressure sodium lights, saving maintenance costs.
To date, the county has installed 100 streetlights in Waimea and 500 in Hilo, with plans to install the remaining 400 in Kailua-Kona. The lights have been purchased with a $500,000 federal grant.
But assuming the new code amendment can be approved by April 2013, the county will move forward with its plan to replace nearly 9,000 streetlights under its jurisdiction (state highways are excluded) at a cost of between $3 million and $4 million.
The cost of the LEDs fluctuates, said Traffic Division chief Ron Thiel, so he could only provide a ballpark figure. In 2011, he estimated the lights might cost between $500 and $1,800, but recently the cost has come down to around the $300 range.
The code amendments that are being drafted would allow developers to switch to LED streetlights if they choose, Thiel said.
“We’re still working with the astronomy people” to preserve viewing conditions on Mauna Kea and save energy, Thiel said.
The astronomers have accepted the increase in blue light from the LED sources.
“It’s a little more blue light, but not very much,” Thiel said.
Last year, at an annual meeting of the astronomy community, members agreed that they were going to have to adjust to the new light sources, said Ron Laub, the light pollution control specialist for the University of Hawaii Institute for Astronomy.
Overall, Laub said the switch to LEDs was a good thing for Hawaii County.
“There’s only a couple of manufacturers left that are making LPS (low-pressure sodium) lamps,” Laub said.
Work to install the LED streetlights is normally done Fridays, Saturdays and Sundays, because those are the times when the traffic levels are low enough at intersections that work can be done.
That also means Department of Public Works employees are racking up overtime, but Thiel doesn’t see it as a problem, calling overtime work “another tool in my toolbox.” He says the increased cost of working outside of regular business hours is roughly offset by the workers’ increased productivity during that time.
Email Peter Sur at email@example.com.