The NEEA and the city of Seattle are hosting a three-night test of LED street lights conducted by the Virginia Tech Transportation Institute in an attempt to determine an optimum balance of dimming lights for efficiency and providing safe object detection distances for drivers.

Seattle, Washingtons Ballard neighborhood is home to the latest round of LED street light testing conducted by the partnership of the Virginia Tech Transportation Institute and Clanton & Associates. The Northwest Energy Efficiency Alliance (NEEA) and the city of Seattle are hosting the test of four different LED-based solid-state lighting (SSL) luminaires, along with an incumbent high-pressure sodium (HPS) light, and a new lower-power HPS lamp.

The goal of the tests is measuring the ability of drivers to detect objects (or pedestrians) at safe distances, while using lower light levels to save energy. Dr. Ron Gibbons of the Virginia Tech Transportation Institute said its important to evaluate lights in terms of visibility rather than light level. He emphasized that, "Lighting level has very little to do with detection."

"These tests will illustrate how LED streetlights use far less energy while maintaining safety and better vision for Seattle residents," said Edward Smalley, director of the U.S. Department of Energy’s Municipal Solid-State Street Lighting Consortium (MSSLC).

Quantitative and qualitative

The tests, the first of which took place on the evening of Tuesday March 6, include having test subjects ride in an SUV instrumented with light sensors, cameras, and a GPS system all linked to a customized control system (see photos). The test subjects are driven through the test course at 35 MPH and depress a button when they spot small 7x7-in objects placed alongside the road. The GPS capability allows the system to capture the exact location for each detected object.

Some of the test subjects will pass through the course with the LED lights at 100% brightness while others will be subject to 50% or 25% brightness levels. The LED luminaires are 105W Philips Lumec products while the incumbent is a 400W HPS light. The other HPS light is a 250W model.

Three of the sets of LED lights vary only in CCT from 3500K to 4000K to 5000K. And there is a fourth set that is also 4000K but that has a new asymmetric beam pattern that Clanton & Associates specified specifically for the testing.

The testing will also include a qualitative survey that is completed by test subjects that walk the test area under the lights. The survey includes questions about the quality of the light, glare, feeling of safety, and other issues.

The team conducting the tests had hoped that Seattle would provide both dry and wet nights allowing an even greater opportunity to gather safety data relative to wet pavement. The worry in Seattle, was whether the team would get a dry night. Alas its dry in Seattle and forecast to be so through the end of the tests on Thursday night. Gibbons said that the city would allow a fire truck to wet the test area on Thursday if the dry forecast holds.

Potential savings

The opening night of the tests drew a contingent of local dignitaries including Seattle Mayor Mike McGinn. McGinn quipped "Who knew that a successful night required rain in Seattle?" McGinn said that Seattle has already installed 20,000 LED lights, second in the US only to Los Angeles, California, and that the short-term goal is 41,000 LED lights. McGinn said, "That’s operational savings of $2.4 million per year."

McGinn discussed the importance of saving energy and the commitment of the community, and said "We have the first carbon-neutral utility in the nation" referring to municipally-owned Seattle City Light. He said some wonder why worry about energy when the utility is carbon neutral. The answer is a projected load growth driven by electric vehicle charging and the server farms that supply data to the continued escalation of consumer devices that connect to the Internet.

Smalley of the MSSLC answered the question about why the focus on LED street lights and energy savings on a much broader scale. He said there are 26.5 million street lights across the US that use $2 billion worth of energy annually. Obviously broad adoption of more-efficient lighting could have a major impact on US energy usage.

About the Author 

Maury Wright is a Senior Technical Editor with LEDs Magazine.

www.ledsmagazine.com