Reporting on pedestrian life in the D.C. area

Are LED street lights the safe, pedestrian boon we imagined?

September 15, 2011 - 02:58 PM
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An LED lamp shines in England. (Photo: flickr/dominic's pics)

Washington, D.C.'s future will, as planned now, be lit by LED street lamps. I talked with a District department of transportation engineer earlier this summer, who told me that DDOT plans to install more than 1,000 LED alley street lamps during the second half of 2011. It's "better power, better color — it's a white color," the man told me. D.C. has a little under 70,000 street lamps as it stands, which included 60,000 high-pressure sodium lights, 6,570 incandescent ones, and 1,000 mercury-vapor lamps when I spoke with the engineer. DDOT has worked with grants of more than a million dollars for the past two years to better develop and integrate LED lighting onto the streets of the District, typically considered a boon over past street lights. More than $100 in federal stimulus money contributed to cities across the U.S. adding more LED street lights in recent years.

Just one problem has emerged — there's a possibility that such LED street lamps may, in fact, be dangerous to pedestrians' health.

According to a new multinational study published in the October 2011 issue of the peer-reviewed Journal of Environmental Management, scientists from Italy, Israel, and the U.S. sought to analyze the effect of different outdoor lamps, including LED lamps. The study, entitled "Limiting the impact of light pollution on human health, environment and stellar visibility," concluded that there are several problems with LED lamps. The new form of lighting would affect the human eye's photoreceptors and cause "scotopic and melatonin suppression bands of more than five times the present levels." In other words, LED lights may well be suppressing our levels of the chemical melatonin, which provides a healthy dose of antioxidants as well as likely helps fight certain cancers.

I won't put words in the scientists' mouths though. Consider this excerpt from the study's abstract, my emphasis in bold:

We evaluated [the lamps'] emissions relative to the spectral response functions of human eye photoreceptors, in the photopic, scotopic and the ‘meltopic’ melatonin suppressing bands. We found that the amount of pollution is strongly dependent on the spectral characteristics of the lamps, with the more environmentally friendly lamps being low pressure sodium, followed by high pressure sodium. Most polluting are the lamps with a strong blue emission, like Metal Halide and white LEDs. Migration from the now widely used sodium lamps to white lamps (MH and LEDs) would produce an increase of pollution in the scotopic and melatonin suppression bands of more than five times the present levels, supposing the same photopic installed flux. This increase will exacerbate known and possible unknown effects of light pollution on human health, environment and on visual perception of the Universe by humans. We present quantitative criteria to evaluate the lamps based on their spectral emissions and we suggest regulatory limits for future lighting.

What does this mean for LED street lamps?

Perhaps nothing yet. This is just one study, and more will likely be needed before anything conclusive can be said about how LED light affects humans. After all, how seriously do these lights affect an individual human? Yet the DDOT engineer called LED street lamps "the future of lighting." I don't intend to monger any fear about the lights here — and at the moment, they truly represent but a small fraction of the many sodium lamps throughout D.C. — but these studies are worth watching. This one's begun to make some waves in various environmental circles but hasn't yet made its way into any deeper discussion. I see no cause for alarm here but perhaps reason to pause and evaluate as we move forward and consider how the District should light the streets with its tens of thousands of street lamps.

Keep watching these reports, D.C., and potentially adjust your lighting accordingly.

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