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Can LEDs replace street lamps? Depends on who's asking

May 22, 2012
Studies find LEDs can and cannot replace sodium-lamped street lights.

When it comes to replacing ordinary street lights with LEDs, you can find evidence that the idea is either impractical or quite feasible.

That seems to be the conclusion that can be reached from recent developments in different cities. For example, the U.S. Dept. of Energy (DOE) recently published the final report from a demonstration of LED technology in ornamental post-top street lights, conducted in Sacramento, Calif. Sacramento and DOE's Municipal Solid-State Street Lighting Consortium evaluated four different LED replacement products using computer simulations, field measurements, and laboratory testing. The study was restricted to lamp-ballast retrofit kits and complete luminaire replacements that would preserve the daytime appearance of the existing acorn-style luminaires.

DOE says the challenge proved formidable, as the results indicate that none of the LED products evaluated could match the performance of the existing 100-W high-pressure sodium (HPS) luminaires. To allow for apples-to-apples economic comparison, the pricing and input power of the LED products were scaled proportionately to represent hypothetical products which would match the HPS light levels.

DOE says the energy used by three of the "scaled-up" LED systems ranged from 63 to 90% of the baseline HPS. The fourth product would actually boost energy use by 15%. And the study concluded none of the products would represent cost effective alternatives to HPS.

But these results didn't dissuade Washington, D.C. from installing LED-based street lamps. Units from Lighting Science Group are going in as part of the first phase of a relighting project there that is said to save the city tens of thousands of dollars each year in energy costs. The Lighting Science Group lights will also cut the District's annual carbon dioxide emissions by 719 tons, officials there say.

"Already results show these new light fixtures are saving energy -- 57 to 60% -- compared to the old mercury vapor and high pressure sodium lights," said Washington, D.C. Mayor Vincent C. Gray.

Working with the Howard University Transportation Research Center, officials from the District Dept. of Transportation (DDOT)analyzed LED lighting products from a variety of vendors and manufacturers. The study involved the evaluation and analyses of photometric readings, fixture life, efficacy, aesthetics, color temperature, dimmability and compatibility with remote monitoring and control systems.

At the conclusion of the Study, DDOT selected Lighting Science Group's Prolific (LSG) LSR-2 LED street light to replace the District's existing alley lights. Said Jim Haworth, chairman and chief executive officer of Lighting Science Group, "Our Prolific Series roadway solutions offer notably longer-life expectancies than the District's existing lights and real reductions in maintenance and energy costs. With less glare and better illumination, uniformity, and color, the new LED street lights signal a true improvement for the District."

The District Department of Energy (DDOE) supported and funded the LED lighting project, under the U.S. DOE Energy Efficient and Conservation Block Grant program. Eventually DDOT plans to install energy-efficient light fixtures throughout D.C., including all of its alleys, streets, bridges, tunnels and underpasses, pedestrian walkways, bike and running trails.

The full report of the DOE Sacramento project is here: http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/2011_gateway-msslc_sacramento.pdf

Lighting Science Group: http://www.lsgc.com/exterior_led_lighting/prolific-roadway/lsr2/

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