Concord’s new LED street lights avoid night glare

A pair of new LED streetlamps are seen along N. Main Street on the first afternoon of Market Days. ELIZABETH FRANTZ / Monitor staff
Downtown visitors walk by two lit trees and a streetlamp on North Main Street as part of a Concord Main Street Project sidewalk up-lighting demo on Wednesday evening. Trees and parts of City Plaza were lit up. Project officials explained the two types of LED lights being considered – a plain white light and a programable colored light – and asked people to provide feedback via a survey. (ELIZABETH FRANTZ / Monitor staff)
A new streetlight is seen on the east side of N. Main Street in downtown Concord on Thursday, June 4, 2015. (ELIZABETH FRANTZ / Monitor staff)

Monitor staff

Published: 6/25/2016 12:10:25 AM

As you enjoy Market Days – or, rather, Market Day nights – you might wonder about the new LED streetlights on the rebuilt portions of Main Street, especially after the Monitor highlighted concern about their effect on stargazing.

Have no fear, or at least less fear: That concern is why the new Main Street lighting is – pardon us while we get geeky – 3,000 Kelvin rather than 4,000 Kelvin.

“We looked at LEDs for the obvious energy-saving opportunities, but one of the things that was important to use was its dark-sky compliance,” said Ed Roberge, Concord city engineer.

By “dark sky” he means the push by astronomical bodies and others to reduce the effects of light pollution, which has been making it harder and harder for us to see the stars, the planets and the Milky Way.

Those groups are alarmed about LED outdoor lighting, which is becoming more common because it saves money by using less electricity and lasts longer than other types of bulbs. The most common LEDs give off a light equivalent to the glow of an object heated to 4,000 degrees Kelvin (about 6,700 degrees Fahrenheit), and that’s the level which has the greatest effect on our night vision.

This is good for lighting because it means we can see better. But that also means this type of light is most effective at overwhelming our view of the night sky.

So aside from making sure the streets on the renovated portions of Main Street are “full cutoff,” a design that keeps the light from being directed upward, Roberge said the city bought bulbs with the equivalent of 3,000 degrees Kelvin, which is much less intrusive to sky-watching.

The 3000K bulbs, as they’re known, have a softer light that fits better into a historic downtown, which is why they were also used during upgrades in Penacook a few years ago.

What did the city pay to avoid the glare of the 4000K bulb? Nothing extra.

“We didn’t see much of a differential cost between 4K or 3K (lighting),” Roberge said.

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)

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David Brooks is a reporter and the writer of the sci/tech column Granite Geek and blog granitegeek.org, as well as moderator of Science Cafe Concord events. After obtaining a bachelor’s degree in mathematics he became a newspaperman, working in Virginia and Tennessee before spending 28 years at the Nashua Telegraph . He joined the Monitor in 2015.