Installment on Bay Bridge Fails to Shine Light on Potential Damage
February 17, 2013
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In the past month, many San Francisco residents and visitors have likely noticed the mesmerizing, expansive light show on the Bay Bridge that is visible from shore, but few may be aware of the reason behind the development and of potential repercussions.
Beginning March 5, 2013, the light exhibition titled The Bay Lights, spanning the Northern face of the Bay Bridge, will be lit for seven hours every night for a period of two years as a tribute to the 75th Anniversary of the Bridge’s existence. The project, headed by Leo Villareal, a New York based light artist responsible for the design and management of the piece, has been in commission for two years already – after the offer was brought about back in 2010.
Some of Villareal’s past light sculptures, displayed on his personal website, have been installed in urban settings throughout the country, lighting up walkways, city parks, and contemporary art galleries. Using individually programmable LED lights engineered into specialized sculptures and arrangements, he programs light patterns using an algorithm, resulting in a constant flux of unique sequences.
To successfully instrument the artistic illumination of the Bay Bridge, Villareal and his team have had to be innovative with the installation of and accessibility to control the lights. In order to view the piece as he works, Villareal programs from shore, communicating wirelessly with control systems installed on the bridge.
Scheduled installation has taken place for over a hundred nights, causing lane closure during work times, between the hours of 11pm and 5am. Raised in baskets, workers have installed strings of white LED lights using industrial zip ties to the vertical suspension cables, with a total of 25,000 individual light nodes, each spaced a foot apart. In compliance with the terms of installment set by CalTrans, each individual node is directed outward on the side of the cables facing the Bay, so as not to impact traffic flow and driver safety.
While the light installment may serve to “unleash all sorts of creativity around the Bay Area”, as Villareal commented in an expository video on the project’s page, there are also potential, and possibly overlooked, consequences of the light show, with respect to the chemical balance of the San Francisco Bay’s atmosphere.
Vehicle emissions release a number of compounds into the air, including single and double (mono- or di-) forms of nitrate oxide, collectively represented as NOx. Another nitrate radical, NO3, is an important natural factor in combating the build-up of smog, as it neutralizes many of the NOx molecules during the night, and helps to cleanse the atmosphere of harmful chemicals.
NO3 is broken apart during the day by wavelengths of red light from the sun into NO2 and O (most often). At night the two separate molecules are able to recombine into NO3, and continue to remove more harmful compounds from the air that were released during the day.
However, light pollution at night hinders the beneficial night-time neutralization of nitrogen oxides. Especially in heavily urban areas, such as the city of San Francisco, light pollution at night has a negative impact on smog levels in the daytime.
A study presented by scientists in 2010 at an AGU (American Geophysical Union) meeting in San Francisco, measured the actinic flux in Los Angeles compared to rural Colorado. They found that the urban glow emitted at night can be up to 25 times stronger than the light of a full moon, causing unnatural disturbance to the atmosphere’s nightly cleansing process.
Using photochemical models to plug in data, Harald Stark, of the NOAA’s Earth System Laboratory, found that city light emissions were responsible for the interruption of nitrate radicals from neutralizing harmful chemicals deposited by vehicle emissions, in some cases causing the destruction of 7% of expected and healthy night-time amounts of NO3s. In turn, the decreased night levels of NO3s can result in daytime levels of NOx being up to 5% higher than they naturally would be.
These detections, specific to L.A. but applicable to all major cities, support the claim that excessive light pollution at night may indeed be detrimental to a healthy atmosphere, and means that the more light pollution in the Bay Area at night, the greater amount of smog present during the day.
And though LED lights are arguably the most efficient type of light bulb yet, high-power white LED’s emit harsh light, still capable of breaking down advantageous atmospheric molecules such as NO3.
I only hope that along with the great care that has been invested in making the light show reality, equally extensive thought has been taken to consider the impact of another 25,000 bulbs shining into our night sky.