City of Cambridge – LED Conversion: Case Study

SMART STREETLIGHTS FOR A SMART CITY IN CAMBRIDGE, MASSACHUSETTS

THE CHALLENGE

With Cambridge being home to two of the most prestigious and technologically advanced universities in America: Harvard and MIT, the City felt as though it too must welcome change and forward thinking. The City of Cambridge committed to reducing their energy consumption by 20% over the course of five years as part of their 2010 sustainability initiative. In addition, the City also sought to improve the management and maintenance of their existing streetlight system.

THE SOLUTION

To reduce energy consumption, the City of Cambridge made a decisive move towards more energy-efficient luminaires by replacing 7,000 high-pressure sodium (HPS) streetlights with new, state-of-the-art light-emitting diode (LED) lights. The City also incorporated wireless adaptive controls into the design of their new LED system.

• Replacement of 4,900 cobra-type fixtures over 9 months, followed by the installation of over 1,000 retrofitted decorative fixtures supplied by King Luminaire Co. Inc.
• The decorative LED fixtures were custom designed to be compatible with their adaptive control system
• Wireless adaptive controls allow for real-time adjustability of light levels, enhanced energy conservation, and energy usage monitoring capabilities
• The LED luminaires only need replacement after approximately 15-20 years, versus re-lamping the old HPS lights every 4-5 years and King Luminaire backs the LED lights with a 7-year warranty

As far as we know, we are the first major city to deploy an adaptive LED lighting system city-wide. This has been an extremely successful process that has far exceeded our expectations and we’ve seen a savings of 80 percent (energy use) so far.

Stephen Lenkauskas, City Electrician, Cambridge, MA

THE RESULTS

Electricity and Maintenance Savings:

• The new LED system saves Cambridge over 75% in electricity every year and reduce bulb replacement frequency by 80%
• The conversion brings significant maintenance savings (estimated lifetime of LED is roughly 4-5 times longer than the old HPS lights)

Energy Cost Savings:

• The use of LED lights delivers energy cost savings of $500,000 each year for a 20-year lifetime, or an equivalent of $10 million
• Eversource, the utility company, contributed over $820,000 in energy rebates toward the cost of LED conversion; the payback period for the first phase of the conversion is 4.36 years
• The LED conversion contributed significantly to Cambridge’s ability to reduce its energy consumption by 20% in 2014, as part of the City’s sustainable initiative goals

Emission Reductions:

• CO2 emissions were reduced by 77%
• After dimming, the LED system emits 40% less light pollution than the old HPS system

Overall:

• The City of Cambridge became the first U.S. city to complete a city-wide LED streetlight retrofit, using adaptive controls that complies with Illuminating Engineering Society (IES) RP- 8-14 standards for roadway illumination