The City of Cambridge initiated a planning study to improve the design and maintenance of its public street lighting system. The effort was prompted by the purchase of 5,000 streetlights from the local utility company that had been operating them.
Primary objectives of the study were to review current street lighting and establish design guidelines for new construction, review and recommend the content of the lighting inventory, and research and recommend emerging light sources and fixtures for evaluation in use. To produce this master plan, WSP worked with a lighting committee composed of staff from several City departments and the historical commission.
Following the initial study, WSP provided preliminary testing and analysis for conversion of the city’s street lighting system to light emitting diode (LED) technology, and continued as sub-consultant for the final design of the conversion.
A key feature is an adaptive control system to vary the light level locally based on expected traffic and pedestrian volumes. Additional pilot installations and tests allowed evaluation of system performance compared to the existing high pressure sodium (HPS) system and to current roadway lighting standards. As such, testing comprised taking readings on the roadway and in pedestrian areas, including vertical illuminance at face level, and evaluating light trespass impacts.
Public response to the initial installations was solicited by the City and has been positive, including response to the use of adaptive controls to dim the lighting system to half output when pedestrian volumes are expected to be low.
The new system—by controlling the light distribution, using criteria from current standards, and implementing adaptive controls--is expected to reduce the power consumption of the new arrangement to less than half of the consumption of the HPS luminaires. Maintenance requirements for the new system are also expected to be lower, about a third of previous expenditures, because of the longer life of the light source.