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LED street lights

LED street lights illuminate the intersection of Houghton and Broadway, Wednesday, Dec. 23, 2015, Tucson.

The American Medical Association has officially warned about the danger that excessive night lighting poses to our health, citing a growing body of medical research on the subject.

In a unanimous vote this month, it adopted a report from its Council on Science and Public Health that advises cities making a switch to LED street lighting to choose bulbs that operate at the “warmer” end of the light spectrum, avoiding the cool “blue” light that approximates bright sunshine.

Tucson, which plans to convert most of its outdoor municipal lighting to LED, or light-emitting diodes, this year, has already chosen the least “blue” lighting that is commercially available and plans to dim those lights when not needed for safety reasons.

The AMA report notes that humans evolved in a world that was not artificially lit.

“With waning ambient light, and in the absence of electric lighting, humans begin the transition to nighttime physiology at about dusk; melatonin blood concentrations rise, body temperature drops, sleepiness grows, and hunger abates,” the AMA reports.

When we spend the evening on streets ablaze with bright light or cuddling with our mobile devices, we disrupt that transition, along with our sleep patterns and eating habits.

Insomnia, obesity, diabetes and even heart disease and some cancers have been potentially linked to our light-filled evenings, said cancer epidemiologist Richard Stevens, a professor of medicine at the University of Connecticut, who contributed to the AMA report.

Stevens published his first study on the potential link between artificial light and breast cancer in shift-workers in 1987.

Since then, a growing body of studies and medical experiments have bolstered the theory that artificial light disrupts the body’s circadian rhythm, with negative health consequences, he said in a telephone interview Thursday.

“We evolved for 3 billion years, and I mean ‘we’ as life on the planet, with the sun for about 12 hours and 12 hours of dark. We have this endogenous circadian rhythmicity.”

We don’t require “pitch dark,” he said. Starlight, moonlight and firelight are “essentially circadian neutral,” he said.

“But then, 130 years ago, that all changed with the electric light bulb.”

There is nothing intrinsically wrong with electric light bulbs or even LED lights, but the lower wavelength LED lights that easily scatter and mimic bright, white daylight should be reserved for daylight hours, he said.

He suggests dimming lights after dusk and letting your body ease into its evening rhythm. “Your body temperature starts to drop, melatonin rises, metabolism slows. We start losing hunger as the hormone leptin rises.”

Melatonin, in addition to being a sleep aid, has been shown to diminish the growth of cancerous tumors in mice, he said.

The International Dark-Sky Association, based in Tucson, praised the AMA action. “We’ve been sounding the alarm on this, basically, for the last six years,” said John Barentine, an IDA project manager.

“The weight of the evidence has been mounting. We just see more and more studies that confirm it,” Barentine said. “This is deep, deep physiology.”

The IDA’s principal reason for reducing outdoor lighting is its advocacy of astronomy, Barentine said, but it also recognizes the adverse effects of over-lighting on humans and the natural world.

The recently published “New World Atlas of Artificial Sky Brightness” found that “about 83 percent of the world’s population and more than 99 percent of the U.S. and European populations live under light-polluted skies.”

The Milky Way, our home galaxy’s sea of stars, “is not visible to 60 percent of Europeans and nearly 80 percent of North Americans,” said researchers led by Fabio Falchi of Italy, who published the atlas in last week’s edition of the journal Science Advances.

Neither Barentine nor Stevens advocates a return to totally dark skies in populated areas. LEDs are a good source of efficient lighting, they said, but city planners need to be careful in selecting the light sources.

Christian Monrad helped sound the alarm about the noxious glare of “blue” LED lighting as president of the IDA in 2009. Cities were switching to them as an energy-saving strategy using federal economic stimulus money, he said.

Monrad, vice president of Monrad Engineering, is working as a consultant on the city of Tucson’s upcoming switch to LED lighting. He said the city wanted to avoid interfering with astronomical observations at nearby observatories, but he and others planning the switch were also aware of the “potential health effects and certain environmental effects.”

Monrad said the American Medical Association is also researching “the much more significant health issue of hand-held devices and E-readers.”

Indoor lighting and the glare from our computer screens and mobile devices also disrupt our physiology, he said. “Think about our evolutionary history. We’re introducing frequencies into our environment that have no precedent.”

Barentine said consciousness of that problem is growing.

There are apps available for changing the lighting on computers and other devices, he said. “It was a pretty significant victory when Apple decided to build that capability into their operating systems for their mobile devices,” he said.

Apple’s setting, known as “Night Shift,” is described on its website:

“Night Shift adjusts the color of your display after sunset. Many studies have shown that exposure to bright blue light in the evening can affect your circadian rhythms and make it harder to fall asleep. Night Shift will shift the colors in your display to the warmer end of the spectrum after sunset, making it easier on your eyes. In the morning, it returns the display to its regular settings.”

That ability to adjust the color of light is also being built into some LED light bulbs, said Stevens.

Stevens said city planners need to consider placement of lighting as well. Light seeping into your home at night, whatever its color, disrupts sleep, he said.

The AMA’s report encourages “the use of 3000K or lower lighting for outdoor installations such as roadways. All LED lighting should be properly shielded to minimize glare and detrimental human and environmental effects, and consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time periods.”

All those features are built into the city’s program, said Monrad.

The city has completed one pilot program for the new LED network, said Michael Graham, spokesman for the Tucson Department of Transportation.

It is installing more lights in the same vicinity, near Fire Station One downtown, this week.

If that is successful, the city will begin installing the new fixtures and lights citywide, beginning after the July 4 holiday in an area near downtown, west of the Santa Cruz River, Graham said.

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