[gary]

In a 22nd Sept article in the Institute of Electrical and Electronics Engineers
(IEEE) Spectrum magazine, Jeff Hecht writes on how some early adopters
of LED street lighting are struggling with glare and light pollution.

Originally Posted by Jeff Hecht, IEEE

For some, those first LED lights have been a fiasco. The harsh glare of certain blue-rich designs is now thought to disrupt people’s sleep patterns and harm nocturnal animals. And these concerns have been heaped on the complaints of astronomers, who as far back as 2009 have criticized the new lights. That’s the year the International Dark-Sky Association, a coalition that opposes light pollution, started worrying that blue-rich LEDs could be “a disaster for dark skies and the environment,” says Chris Monrad, a director of IDA and a lighting consultant in Tucson.

When my city of Newton, Mass., announced plans to install LED streetlights in 2014, I was optimistic. I’m all for energy conservation, and I was happy with the LED bulbs in my home office. But months later, returning from a week’s vacation in rural Maine, I was shocked to find my neighborhood lit by a stark bluish blaze that washed out almost all of the stars in the night sky.

Lately, lighting companies have introduced LED streetlights with a warmer-hued output, and municipalities have begun to adopt them. Some communities, too, are using smart lighting controls to minimize light pollution. They are welcome changes, but they’re happening none too soon: An estimated 10 percent of all outdoor lighting [PDF] in the United States was switched over to an earlier generation of LEDs, which included those problematic blue-rich varieties, at a potential cost of billions of dollars.

The episode invites a few questions: How did an energy-saving technology that looked so promising wind up irritating so many people? Why has it taken so long for the impacts of blue-rich lighting to become widely known? And why did blue-rich LEDs so captivate municipal lighting engineers long before better options reached the market?

Originally Posted by Jeff Hecht, IEEE

Whatever their faults were, those blue-rich LED lights do save energy and money. My city of Newton, Mass., which has about 80,000 residents, expects to save US $3 million over 20 years after swapping its 8,406 sodium streetlights for 4,000-K LEDs, and avoid 1,240 metric tons of carbon dioxide emissions annually. Los Angeles anticipates saving $8 million a year after installing more than 150,000 LED streetlights, [PDF] while New York City hopes to recover $14 million a year by replacing the city’s 250,000 streetlights with LEDs.

Originally Posted by Jeff Hecht, IEEE

Our visual sensitivity shifts as light grows dim because rods and cones respond most strongly to waves of different lengths. The collective response of cones makes the human eye most sensitive in daytime to wavelengths of green-yellow light in the middle of the visible spectrum. Rods have a peak response to shorter blue-green wavelengths. Blue-sensitive cones, which are greatly outnumbered by other types of cones but are thought to play a role in sensing brightness at night, peak at wavelengths that produce indigo light.

The result is that at night the blue-rich light from an LED streetlamp looks brighter to the eye than the orangish light from a high-pressure sodium lamp—even if the two emit the same number of lumens, which are measured on a scale based on the eyes’ daytime response.

Given these facts, some experts touted bluer light for LEDs, noting that the relatively high color temperatures could enhance visibility at night. Some suggested that the use of bluish LEDs would let us see so much better at night that we could turn down the intensity of the lighting.

Yet Ron Gibbins, director of the Center for Infrastructure-based Safety Systems at the Virginia Tech Transportation Institute, says his experiments don’t support that idea. He has found that drivers’ eyes do not fully adapt to the dark, and thus would benefit little from the higher sensitivity of rods to blue light.

Other peer-reviewed studies have found that portions of the retina can adapt to different light levels at the same time. This suggests that rods focused on a road’s periphery may be better adapted to lower light levels, and therefore stand to benefit more from blue-rich lighting than those focused on the center line.

Article here -
http://spectrum.ieee.org/green-tech/...oods-the-blues