As for LED streetlights: they do appear to be a best buy, say Pitt researchers
Pittsburgh, PA--Researchers at the University of Pittsburgh have conducted a "cradle-to-grave" assessment of LED streetlights and determined that, compared to other types of lamps, LEDs strike the best balance between brightness, affordability, and energy and environmental conservation, at least when their entire lifespan--from production to disposal--is considered.
Engineers in the Mascaro Center for Sustainable Innovation based in Pitt's Swanson School of Engineering compared LED streetlights to the USA's two most commonly used lamps--high-pressure sodium (HPS) and metal halide--as well as to the induction bulb, another emerging technology billed as bright and energy efficient. The result: LEDs may carry a formidable price tag, but in comparison to HPS and metal halide lamps consume half the electricity and last up to five times longer. Induction lights proved slightly more affordable and energy-efficient than LEDs, but may also have a greater environmental impact when in use. The authors also noted that LED technology exhibits more potential for improvement and may surpass induction lamps in the future.
Many cities looking at LED streetlights
The survey coincides with initiatives in several US cities to replace HPS lamps with LEDs. (High-pressure-sodium lamps have that unattractive pinkish-orange glow, which gives them a very low color-rendering index, or CRI. A CRI of 100 is an ideal white light, while a CRI of 0 is the result of a single narrow spectral line; the HPS lamp has a CRI that hovers somewhere down around 24. In contrast, high-quality LEDs can have a CRI of greater than 90.)
The City of Pittsburgh commissioned the Pitt report as it considers replacing 40,000 streetlights with LEDs, in a program similar to retrofits and pilot programs underway in cities from Los Angeles and San Francisco to Raleigh, NC, and Ann Arbor, MI. The City of Pittsburgh estimated that, per year, replacing HPS lamps with LED streetlights would save Pittsburgh $1 million in energy costs and $700,000 in maintenance, while reducing carbon dioxide emissions by 6,818 metric tons.
The group created a "life-cycle assessment" for each type of lighting technology, with information pulled from sales companies, manufacturers, government documents, lighting professionals, and industry reports. The assessments catalog the environmental effect of the streetlamps during their complete lifespan, from the extraction of raw materials and assembly to electricity consumption and disposal.
LEDs actually led the other technologies in negative environmental and health effects during manufacturing, according to the report. LEDs must be embedded in circuit boards that require numerous raw materials, need considerable energy to produce, and can be difficult to recycle. Otherwise, the production of LED housings--composed largely of plastic and wire--consumes far less energy than manufacturing aluminum-heavy HPS casings. LED bulbs also contain no mercury and fewer toxins, such as iodine and lead; HPS and metal halide bulbs packed an average 15 mg of mercury each, with induction bulbs averaging 6 mg per bulb.
Induction bulbs not bad, though
During a bulb's lifetime, however, electricity consumption produces up to 100 times the environmental impact of manufacturing, the authors wrote. LED lights consume 105 W, compared to a hefty 150 W for HPS and 163 W for metal halide. With electricity consumption converted into kilograms of carbon dioxide produced, metal halide bulbs would emit nearly 500 million kg of carbon dioxide during 100,000 hours of use, followed by HPS bulbs with more than 400 million kg, induction bulbs with approximately 350 million kg, and LEDs producing slightly more than 300 million kg.
The report also gauged the four technologies in terms of output of nitrogen oxides and chlorofluorocarbon (CFC). In both categories, LEDs ranked the highest during the bulb-manufacturing stage but the lowest during actual use. In use, metal halides produced the greatest emissions of both pollutants.
Be careful when shopping for LEDs
As for cost, the prices of LED lights are highly inconsistent--the team estimated a range from $9.20 to $322 per fixture. But the technology's considerably longer lifespan could mitigate the sticker shock. Based on 100,000 hours of use, LEDs did not last as long as induction bulbs--which were estimated to cost $280 per fixture--but should burn nearly three times longer than HPS lights and almost five times longer than metal halide lamps. As an example, 40,000 LED lamps could initially cost the City of Pittsburgh as much as $21 million versus approximately $9 million for metal halide streetlights. Yet replacing metal halides could cost as much as $44 million before the LED lamps needed a first replacement.
The Pitt report also addresses non-life-cycle issues, including choosing an LED vendor. The authors recommend that city governments not simply select the lowest bidder--because the technology is new and still developing, a company specializing in LED lamps might not necessarily be the most experienced with installing and managing them. They recommend that municipalities not only consider a company's age and past performance, but also seek out vendors that have had their technology vetted by independent laboratories. They also indicated that larger businesses may have more R&D resources for upgrading their technology.
What's next?
In general, the LED market is seeing unprecedented growth, even though at the moment most people still encounter high-brightness LEDs mostly in specific applications such as holiday lights, traffic lights, display backlights, and automobile taillights. Backed by much investment in the industry, the LED is being pushed to become the next big general-illumination source.
So, will the streetlight of the future be the LED or the induction lamp? In my view, a healthy competition would be the best thing for everyone. Induction-lamp R&D departments--now's your chance!
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.